Laurence Croguennec

Philippe Dagault

Stanislav Pechev

Je Souhaite Particulièrement Remercier Alain

Lydie Bourgeois

Dmitry Filimonov

Hwang

Keywords: Na batteries, positive electrode materials, sodium layered oxides, electrochemical intercalation / deintercalation mechanisms -

Structural and electrochemical studies of Na x Mn 1-y Fe y O 2 and NaNiO 2 materials used as positive electrode materials for Na-ion batteries

Titre : Etudes structurales et électrochimiques des matériaux Na x Mn 1-y Fe y O 2 et NaNiO 2 en tant qu'électrode positive de batteries Na-ion

Résumé :

Ce travail présente les études électrochimiques et structurales menées sur deux systèmes : P2/O3-NaxMn1-yFeyO2 et O'3-NaxNiO2 utilisés en tant que matériaux d'électrode positive pour batteries Na-ion.

Concernant le système P2/O3-NaxMn1-yFeyO2, l'étude par diffraction des rayons X menée in situ pendant la charge de batteries a montré de nombreuses transitions structurales. Que leur structure soit de type P2 ou O3, les matériaux présentent une phase distordue pour les taux d'intercalation (x) les plus élevés et une phase très peu ordonnée pour les taux d'intercalation les moins élevés. Entre ces deux états d'intercalation, les phases de type P2 présentent moins de transitions que les phases de type O3. Cela entraine de meilleures propriétés électrochimiques pour les phases de type P2 (meilleure capacité en décharge, meilleure rétention de capacité…). Les spectroscopies d'absorption des rayons X et Mössbauer du 57 Fe ont montré que les couples redox Mn 4+ /Mn 3+ et Fe 4+ /Fe 3+ sont impliqués lors du cyclage, à bas et haut potentiel, respectivement.

Concernant O'3-NaNiO2, la diffraction des rayons-X menée in situ pendant la charge de batteries O'3-NaNiO2//Na a montré de nombreuses transitions structurales O'3 ↔ P'3 résultant du glissement des feuillets MO2. Ces transitions s'accompagnent de mises en ordre Na + -lacunes dans le matériau. La taille des grains a montré avoir un intérêt majeur puisqu'elle influe sur le nombre de phases présentes simultanément dans le matériau. Lorsque la batterie est déchargée, la phase limitante Na≈0. Finally I would like to thank the members of Groupe 2, my friends and my family. They will find better acknowledgments in French in the following.

-10-ecological issues if they decide to adopt polluting energy sources such as coal. A solution to this problem would be to encourage the transition towards greener energy sources, such as solar and wind farms.

However, this remains a utopia as the associated energy production is still unforeseeable and intermittent.

-18-The use of Li-ion batteries once seemed appealing to regulate the energy production but the price of the raw materials and the energetic price of manufacturing the batteries were so high, it would wipe out any benefit represented by the green energy sources.

In this context, the Na-ion battery technology, that was for a long time set aside, was revisited in the 2000s. Indeed, as the regulation of the energy production from renewable sources requires stationary batteries, the lower mass and volume energy densities of the Na-ion technology do not represent a problem anymore. New criteria are thus established for these applications, which are the price, abundance and eco-compatibility of the materials [22]. As a consequence, the number of studies on NaxMO2 materials involving non-toxic or less-toxic transition metals elements (M = Mn, Fe, Ni…) increased significantly in the 2000s [22][23][24][25]. In the present work, we focused on two systems were studied among NaxMO2 materials:

Investigations in the NaxMn1-yFeyO2 system. This topic represents the first part of this manuscript. Among NaxMO2 systems involving several transition metals, the NaxMn1-yFeyO2 one was never studied for its electrochemical properties in 2011 -starting date of this thesis -despite representing a low-cost and environmental friendly candidate with an interesting theoretical discharge capacity of ≈ 240 mAh.g -1 .

Following Yabuuchi's et al. work of NaxMn1/2Fe1/2O2 materials in 2012 [26], several studies were released concerning the electrochemical and structural properties of various NaxMn1-yFeyO2 materials [27][28][29][30][31][32][33].

The first chapter of our study of NaxMn1-yFeyO2 materials focuses on the preparation and characterization of the pristine materials with y = 1/3, 1/2 and 2/3 with P2 and/or O3 structures (Chapter A-I). These materials were prepared by a self-combustion type synthesis I approached during my Master's degree internship in LRCS, Amiens, FRANCE with Dr. V. Viallet. Most extensive studies are then presented and focus mainly on the limitations of the different materials and on their behavior while cycling in Na batteries (Chapters A-II and A-III). These studies include electrochemical tests in various conditions, in situ X-ray powder diffraction during Na + deintercalation, structural resolutions and following of the redox properties upon Na + deintercalation. These last studies were part of the Franco-Taiwanese LaNaMox ANR project 2 and were the opportunity for me to go to Taiwan and to the Synchrotron facility 3 . The evolution of the electrochemical and structural properties along with the Mn / Fe ratio is discussed in Chapter A-IV. 2 Blanc Inter II, SIMI 8 n° 2011-IS08-01, in partnership with NTUST, Taiwan, R.O.C. 3 National Synchrotron Radiation Resource Center, Taiwan, R.O.C.

-19-Investigation of the O'3-NaNiO2 phase diagram. While NaxMO2 materials were not studied for Naion batteries applications for nearly two decades, numerous studies focused on the correlation between their structure and physical properties, especially concerning NaxCoO2. Following a similar approach, the second part of this work concerns the preparation and characterizations of NaxNiO2 phases (Chapter B-I).

The evolution of the NaxNiO2 phase diagram upon cycling was also investigated by in situ X-ray powder diffraction during the full charge of a NaxNiO2//Na cell. Our choice of the NaxNiO2 phase diagram followed the study of Vassilliaras et al. who reported in 2012 the long-term electrochemical properties of O'3-NaNiO2 along with an insight of the structural changes the material undergoes upon cycling [34]. The purpose of this first chapter is to give the keys required to understand the state of art of sodium layered oxides (NaxMO2). First the different structures of sodium layered oxides are described.

Then, the principle of Na and Na-ion batteries are presented with the main electrochemical quantities employed to compare the different materials. The last part of this chapter is a bibliographic study on NaxMO2 materials. The first described AxMO2 layered oxide (A = alkali element and M = transition metal(s)) was the α-NaFeO2 one, using the NaCl rock salt structure type [1]. In this representation, the O 2-ions occupy the Cl -position, creating a face-centered cubic network. The Na + and Fe 3+ cations occupy the octahedral NaO6 and FeO6 sites created by the oxygen anions, respectively (the former Na + octahedral sites in NaCl). The difference in the ionic radii of the two ions (rNa + = 1.02 Å and rFe 3+ = 0.645 Å) imposes an altering of the Na + and Fe + ions along the [111] direction, as shown in Nowadays, most of the layered oxides are described using a hexagonal cell instead of the rhombohedral one. In this representation the chex axis is parallel to the previous (111)cubic direction highlighting the cationic ordering along the chex axis: the edge-sharing FeO6 octahedra create the (FeO2)n layers while Na + ions occupy the interlayer space, as shown in Figure I.2.

Figure I.2:

Representation of the α-NaFeO2 structure in the hexagonal symmetry (the unit cell is shown by black lines) highlighting the altering of the FeO6 and NaO6 octahedra layers along the chex axis. Cell and atomic parameters from [35].

I.1.b. Other NaxMO2 structures

Due to its large ionic radius, Na + ion can also accommodate trigonal prismatic sites between the structure types is also represented.

In the O3 structure type, the oxygen layers stack along the direction following an ABCA… sequence. This is the structure type of α-NaFeO2. Na + ions are located into octahedral NaO6 sites which only share edges with the surrounding MO6 octahedra. Materials with an O3 structure type are commonly obtained for a Na/M ratio equal or close to one [36], independently of the transition metal: M= Ti, V, Cr, Mn, Fe, Co… [1,4,5,[37][38][39]. The low repulsions between the NaO6 octahedral sites allow filling up the sodium sites completely. This structure type is also the only one possible for LiMO2 materials prepared by solid state chemistry synthesis, because of the small ionic radii of the Li + ion (0.76 Å).

In the P3 structure type, the oxygen layers stack following an ABBCCA… sequence and the Na + ions occupy prismatic sites sharing faces and edges with the surrounding MO6 octahedra. P3 phases are usually obtained at moderate temperature (≈ 500 °C) and for lower Na/M ratios (≈ 0.5) [36].

The P2 structure type shows an ABBA… stacking sequence of the oxygen layers and the Na + ions also occupy prismatic sites. However these sites are different from the P3 structure as the NaO6 polyhedra share either edges (Nae site) or faces (Naf site) with the surrounding MO6 octahedra. Due to higher electrostatic repulsions between the Naf + and M n+ ions, the Naf site is less favorised and the observed Naf : Nae ratio is usually close to 1 : 2 for x ≈ 0.7. Note that adjacent Nae and Naf sites cannot be occupied - 25-simultaneously. These materials are commonly obtained by solid state chemistry synthesis for a Na/M ratio inferior to 1 (usually ≈ 0.7) [36].

The space groups and atomic positions used to describe the O3, P3 and P2 structures are given in Table I.1. The table also shows that only the atomic positions of the oxygen and sodium ions differ between the O3 and P3 structure types. Moreover, for P3 and P2, the crystallographic sites for Na + ions cannot be fully occupied because the distance between two nearest sites is too short and is incompatible with the Na + size. I.1: Usual space groups and atomic positions for the O3, P3 and P2 structure types.

Structure type

I.1.c. Distorted structures and the cooperative Jahn-Teller Effect

Presentation of the Jahn-Teller effect

In 1937, H.A. Jahn and E. Teller proved the theorem stating that "any nonlinear molecular system in an electronic state with orbital degeneracy will be unstable and will undergo a distortion to lower its symmetry in order to lift the degeneracy and lower the energy" [40]. A simplified interpretation is that for some electronic configurations of transition metal ions (M n+ ), the associated ML6 octahedra (L = Ligand) will be distorted. However, the Jahn-Teller theorem predicts only that a distortion must occurs to lift the degeneracy but does not predict the geometrical nature of the distortion, which will commonly consist in either the elongation or shortening of the M-L bonds along the z axis of the octahedron.

In transition metal solid state chemistry, strongest Jahn-Teller effects are expected for the electronic configurations with unevenly occupied eg orbitals such as [START_REF] Cotton | Basic Inorganic Chemistry[END_REF][START_REF] Atkins | [END_REF]:

-High-spin (HS) d 4 (t2g 3 eg 1 ): HS Cr 2+ , Mn 3+ , Fe 4+ … -Low-spin (LS) d 7 (t2g 6 eg 1 ): LS Ni 3+ , Co 2+ … -LS d 9 (t2g 6 eg 3 ): LS Cu 2+ , Ag 2+ … -26-

The electronic configurations and lifts of degeneracy concerning the HS d 4 - 27-In the AxMO2 materials, each MO6 octahedron is connected to 6 MO6 octahedra by sharing edges.

Therefore, if the fraction of M(Jahn-Teller)O6 distorted octahedra is high enough, the distortion can affect the surrounding M(non Jahn-Teller)O6 octahedra and a cooperative Jahn-Teller effect is observed. In NaxMO2 materials, the cooperative Jahn-Teller effect leads to the macroscopic distortion of the hexagonal symmetry. A prim symbol is added to the nomenclature to differentiate the corresponding distorted materials: P'2, P'3 or O'3. A projected representation of the distorted structures is given in Figure I. 5 below. Note that the prim symbol is also used to describe distorted materials whose distortion does not result from a cooperative Jahn-Teller effect.

Figure I.5:

Projections of the distorted structures in the (amon.,cmon.) and (amon.,bmon.) planes (O'3, P'3) or in the (borth.,corth.) and (aorth.,borth.) ones (P'2). P'2 structure types exhibit orthorhombic crystal symmetry whereas the O'3 and P'3 structure types exhibit a monoclinic one. The only differences between the O'3 and P'3 structures are the atomic positions of the oxygen and sodium atoms. The space groups and atomic positions used to describe the P'2, P'3 and O'3 structures are given in Table I.2. I.2: Usual space groups and atomic positions for the P'2, P'3 and O'3 distorted structure types.

Structure type

Relations between the hexagonal cells and the orthorhombic and monoclinic cells

It is possible to describe the undistorted hexagonal structures into the orthorhombic or monoclinic cells. The relations between the hexagonal symmetries and the lower ones for an undistorted example are given in Table I For phases with undistorted structure, the borth. or amon. cell parameter is equal to √3 bhex..

Therefore the comparison between the undistorted and distorted cells will give precious information on the origin of the distortion in the P'2, P'3 or O'3 structures, through the borth./aorth. or amon./bmon. ratio:

-If the borth./aorth. or amon./bmon. ratio is close to √3 (≈1.73), the Jahn-Teller distortion is negligible.

-If the borth./aorth. or amon./bmon. ratio is significantly higher than √3, the distortion is considered as being induced by a cooperative Jahn-Teller effect.

The correlation between the borth./aorth. or amon./bmon. ratio and the cooperative Jahn-Teller effect was first reported by Parant et al. in 1971 in NaxMnO2 materials [5].

I.1.d. Determination of the distances in the hexagonal and distorted structures

From the cell parameters it is possible to obtain an estimation of the interslab distance between two layers of transition elements and the in plane transition metal distances. A representation of the interslab and the in plane M-M distances in the orthorhombic and monoclinic cells is given in Figure I.7.

The relations between the crystal structure and the interslab and in plane distances are given in Table I.4. (long M-M distance)

Table I.4: Relations between the cell parameters of the different structures and the interslab and in plane M-M distances.

Examples of the cooperative Jahn-Teller effect in O'3-NaNiO2 and O'3-NaMnO2

An example of the importance of the cooperative Jahn-Teller effect in O'3-NaNiO2 and O'3-NaMnO2 is given in Table I. 5. In these materials, 100 % of the involved transition metal ions present a Jahn--31-Teller effect (LS 3d 7 for Ni 3+ and HS 3d 4 for Mn 3+ ). The amon./bmon. ratio highlights a stronger cooperative I.5: Cell parameters, amon./bmon. ratios and M-O distances in O'3-NaNiO2 and O'3-NaMnO2. O'3-NaNiO2: data from [43], O'3-NaMnO2: data from [44].

I.2. NaxMO2 layered oxides as positive electrode materials in Na and Naion batteries I.2.a. Principle of Na and Na-ion batteries

The Na-ion battery technology involves materials able to exchange sodium ions between two electrodes. Depending on the chemical potential of these electrodes are associated the terms of positive electrode (higher potential) and negative electrode (lower potential), in order to avoid the cathode and anode terms which can be confusing as they depend if the battery is charged or discharged. The two electrodes are separated by an electrolyte, which usually consists in a sodium salt dissolved into a nonaqueous solvent. For a Na cell, the assembled battery is represented in its initial state in Figure I.8a.

During the electrochemical charge of the battery, a current is applied to oxidize the transition element(s) constituting the positive electrode and to reduce the Na + ions at the negative one. To balance the charge neutrality of the material, Na + ions are deintercalated from the structure at the positive electrode and go into the electrolyte, as illustrated in The nature of the negative electrode gives the denomination of the technology. If the negative electrode consists in sodium metal, the battery will be referred to as a Na battery. On the other hand, if the negative electrode is an insertion / alloy / conversion compound which doesn't involve the reduction of Na + ions in Na metal, the battery will be referred to as a Na-ion battery by analogy to the Li-ion technology. The use of an alkali metal foil (Li or Na) leads to the formation of dendrites during the charge (visible in Figure I.8b), which grow as the cycle number increases, the result being the degradation of the battery by short circuit. Therefore, the Na battery technology is limited to the study of the materials at the laboratory scale and is unsuitable for real applications. A lot of researches are ongoing to find materials which can insert Na + at low voltage. Among them hard carbon is one of the best materials so far [45][46][47].

I.2.b. Electrochemical variables

Several variables are used to compare and evaluate the performances of batteries. Three of them -the sodium content, the discharge capacity and the charge/discharge rate-were mostly used in this work and are described in the following.

Sodium content

The sodium content, noted x, expresses the concentration of Na + ions intercalated in the material at a given moment. For NaxMO2 materials, it corresponds to the Na/M ratio. The number of (de)inserted ions Δx can be deduced from the capacity (Q) knowing the value of applied current and time of application of the current, as follows: -34-

% = &

Discharge capacity

The discharge capacity represents the amount of electrical charges given by the electrochemical system. For comparison purposes, it is expressed as per mass of active material. The theoretical discharge capacity is given by the following formula: % = H*. (

IJ

With:

% : theoretical capacity per mass of active material (A.h.g -1 )

Δ*: number of inserted e -(or Na + )

F: Faraday's constant = 96485 C.mol -1 Mw: Molar weight of NaxMO2 at x0 (g.mol -1 ) x0: initial intercalation amount in the material

(I.2)
Experimentally, only a fraction of the Na + ions can be (de)inserted during the cycling of the battery and the experimental discharge capacity never reaches the theoretical one.

Charge / discharge rate

The rate corresponds to the current value applied in order to reach the theoretical charge / discharge capacity in ' hours. It is given by the following formula:

&' = %

With:

&: current value (A)

': expected duration of the (dis)charge (hours)

% : theoretical capacity per mass of active material (A.h.g -1 )

(I.3)
The rate is noted C/t. This notation implies that the requested time (hours) to reach the theoretical charge or discharge capacity is equal to t. For example a C/20 rate means that the battery would be fully charged or discharged in 20 hours. Because of thermodynamics and kinetic effects, the rate will impact the amount of Na + ions accessible in the material within a given voltage window: a high rate value will usually lower the number of extracted / inserted Na + ions.

I.2.c. The galvanostatic curves

The variations of the voltage of the battery (E) as a function of the sodium content (x) or galvanostatic curve give precious information concerning the structural changes the materials undergo upon cycling. Three kinds of behaviors can be observed on the E = f(x) curves, as represented in (1) The voltage suddenly increases or decreases and marks a "jump" on the E = f(x) curve. This is characteristic of a peculiar composition and highlights the existence of a single phase with a welldefined structure. Very often it is a stoichiometric phase or a supercell with ordered cation distribution [48]. The composition domain for the existence of such phases is very narrow.

(2) The voltage does not evolve with the Na content and creates a plateau. This behavior is characteristic of a biphasic domain e.g. there is equilibrium between two phases of different compositions and structures. Only the ratio between these two phases evolves along the plateau.

(3) The voltage evolves continuously as a function of x. This is the signature of a solid solution. The structure remains the same, only the sodium amount varies constantly during the sodium (de)intercalation.

All the voltages mentioned in the present manuscript will be expressed vs. the Na + /Na redox couple.

E (V vs. Na + /Na)

x in Na x MO 2 Biphasic domain (2) Peculiar composition (1) Solid solution

I.2.d. NaxMO2 layered oxides in the literature

The study of the electrochemical properties of the NaxMO2 layered oxides is marked by two main periods of an important number of publications. The first one happened in the 1980s and corresponds to the exploration of several NaxMO2 materials along with LiMO2. NaxMO2 materials involving only one transition metal were mostly studied.

The second period started in the 2000s and is still ongoing in 2014. The advanced electrochemical properties of some NaxMO2 involving one transition metal were revisited and new NaxMO2 materials of mixed composition on the M site were synthesized and characterized.

NaxMO2 materials involving one transition metal

NaxMO2 materials involving one transition metal were the first to be studied, long before the search for positive electrode materials. The first NaxMO2 materials with M = Fe [1], Co [3,4,49,50], V [9,39], Cr [9] or Ni [2] were synthesized to study their physical and / or structural properties. Then the search for positive electrode materials lead to the investigation of their electrochemical properties, starting with the P'3-Na0.6CoO2, P2-Na0.7CoO2, O'3-Na0.77CoO2 and O3-NaCoO2 materials by Delmas et al. in 1981 [51].

The electrochemical activity of these materials i.e. their ability to reversibly (de)intercalate the Na + ion was demonstrated. Following the same reasoning, other NaxMO2 were reinvestigated to confirm their electrochemical activity such as O'3-NaNiO2 [38], O3-NaCrO2 [38], P2-NaxMnO2 [52], O'3-NaMnO2 [52] and O3-NaTiO2 [53]. In the early 2010s, more advanced studies of the electrochemical properties were performed on these different materials along with new ones (P2-Na0.7VO2 and O3-NaVO2 [54][55][56]). The results are summed up in Table I [63]

NaNiO2 O'3 1.25 -3.75 V ≈ 150 mAh.g -1 (C/10) 80 % (20 cycles) [34] Table I.6: Electrochemical properties of different NaxMO2 materials. All voltages ranges are expressed versus the Na + /Na redox couple.

The galvanostatic curves of most of these materials exhibit several voltage jumps due to the existence of Na / vacancy orderings [34,38,44,48,51,[53][54][55][56][57][58][59][60][61]64]. On a structural point of view, the Na / vacancy orderings create a superstructure which is often indexed based on the substructure lattice parameters. In some of these materials, the peculiar compositions are separated by biphasic domains indicated by voltage plateaus [34,38,44,48,51,[53][54][55][56][57][58][59][60][61]64].

It is noteworthy that NaFeO2 and NaTiO2 are the only NaMO2 materials with one transition element that do not show intermediate peculiar phases [53,62]. It is suggested that the instability of the Fe 4+ and Ti 4+ cations leads to their migration to the interlayer space [35,37].

The structural transitions resulting from MO2 slabs glidings [36] can represent an important problem concerning battery applications if they lead to the degradation of the positive electrode material, as for O3-NaFeO2. On the other hand, the huge voltage jumps can be hard to predict and represent a problem for monitoring the battery behavior. Materials showing a continuous variation of the voltage along with the Na content are usually preferred.

NaxMO2 materials with mixed occupation of the M site

The substitution or partial replacement of the transition metal is an interesting way to improve the electrochemical properties of the NaxMO2 materials by impacting the following criteria:

• It sometimes stabilizes the materials on a wider sodium composition domain by preventing structural transitions. For example, several studies focused on the replacement of Fe into O3-NaFeO2 by Mn [26-33, 65, 66], Ni [START_REF] Wang | [END_REF], Ni + Co [68] or Ni + Mn [46,69] in Nax[LiyNizMn1-y-z]O2 [70,71]. The in situ X-ray powder diffraction (XRPD) characterization of P2-Nax(Li0.12Ni0.22Mn0.66)O2 showed no P2 → O2 transiion upon charge, as it was evidenced for P2-NaxNi1-yMnYO2 [72].

• The substitutions are a way to stabilize new structural types that cannot be obtained with only one transition element. For example, the only structure types accessible for Ni and Fe based sodium layered oxides are the O'3-NaNiO2 and O3-NaFeO2 ones. Thanks to the partial replacement of the Ni and Fe transition metals, different studies report the synthesis of various P2 materials in the P2-NaxFe1-yMnyO2 [26,[28][29][30][31][32][33][START_REF] Yabuuchi | th ECS Meeting Abstract #[END_REF] and P2-NaxNi1-yMnyO2 [72][73][74][75][76][77][78] phase diagrams.

• Moreover, the substitutions reduce or suppress the important voltage jumps associated to the Na/vacancy orderings previously discussed. For instance, the Mn substitution in the P2-NaxCoO2 material suppress almost every voltage jump except for the x = 1/2 one [79].

Following these reasonings, several new P2 and O3 materials were synthesized and characterized.

Their electrochemical properties are summarized in The preliminary works of Parant in the 1970s showed the feasibility of the Mn substitution in O3-NaFeO2 and highlighted two structural domains (P2 and O3) depending on the Na content [START_REF] Parant | Sur quelques nouveaux oxydes ternaires du système manganèse -oxygène -sodium[END_REF]. The studies of Sharma et al. [START_REF] Sharma | [END_REF] and Paulsen et al. [74] on NaxMn1-yCoyO2 materials were completed in 2011 by Carlier et al, showing that P2-Na2/3Mn1/3Co2/3O2 was electrochemically active in a Na cell [79]. It must be noted that no long-term electrochemical study was yet carried out on the O3-NaNi0.6Co0.4O2 material synthesized by Saadoune et al. in 1996 [83]. The first study of the NaxNi1-y-zMnyCozO2 system, which represents one of the most promising positive electrode materials for Na-ion batteries, is attributed to

[85]

[85] (1) Materials with P2 structure type allow reaching higher capacity than those with O3 one.

NaxMn1-yFeyO2 P2-Na2/3Mn2/3Fe1/3O2 2.0 -3.8 V 2.0 -4.5 V 1.5 -4.3 V ≈ 155 mAh.g -1 (C/
NaxNi1-y-zMnyCozO2 P2-Na0.7Ni0.3Mn0.6Co0.1O2 1.7 -4.0 V 1.5 -4.0 V 1.7 -4.3 V ≈ 125 mAh.g -1 (C/20) ≈ 160 mAh.g -1 (C/
(2) Some of the materials exhibit a capacity retention superior to 90 % after at least 10 cycles for Crates comprised between C/20 and 1C: P2 and O3-NaxMn1-yNiyO2 [57,76,78,85], P2-NaxMn1-yFeyO2 [30,[START_REF] Yabuuchi | th ECS Meeting Abstract #[END_REF],O3-NaNi1/3Co1/3Fe1/3O2 [68], P2-NaxNi1-y-zMnyCozO2 [90,93], P2-NaxNi1-y-z-wMnyCozAlwO2

[93] and P2-NaxNi1-y-zMnyLizO2 [70].

However, due to the very different experimental conditions, it is impossible to conclude on the best positive electrode material: the voltage ranges have a huge impact on the cyclability as a too high upper voltage can lead to the material degradation. For example, the O3-NaMn1/2Ni1/2O2 exhibits an interesting capacity retention of 91 % after 100 cycles when cycled between 2.0 and 4.0 V [85] but this capacity retention drops to 29 % if the upper voltage limitation is increased to 4.5 V [85]. Therefore, one must be precautious when comparing one system to another.

Towards high voltage batteries: improving the electrolyte

Around the world, people working on Na-ion batteries have to face another important problem which is the electrolyte degradation. The organic solvent-based electrolyte tends to decompose at the low and / or high voltage. To overcome this issue, several sodium salts (NaClO4, NaPF6 or NaCF3SO3 [96]) and organic solvents (Propylene Carbonate (PC), DiEthyl Carbonate (DEC), DiMethy Carbonate (DMC), Ethylene Carbonate (EC)…) were studied with or without adding an additive (FluoroEthylene Carbonate (FEC)) to reduce the decomposition issue [97]. If the use of Vinylene carbonate (VC) in Li-ion batteries electrolyte was already shown to efficiently reduce the electrolyte decomposition issue [98], no study is reported yet on its impact on Na-ion batteries electrolyte. The NaPF6 in PC and NaClO4 in PC electrolytes usually decompose for E > 3.5 V vs. Na + /Na [48]. The NaPF6 in EC/DEC electrolyte exhibits better stability [96], as for the NaPF6 in PC + 2wt % FEC one [99]. The search for a stable electrolyte assuring maximum stability demands a rigorous and fastidious work that Bhide et al. started in 2014 [100] by comparing electrolytes made of the different sodium salts (NaClO4, NaPF6 and NaCF3SO3) dissolved into an EC + DMC mixture under different cycling conditions (salt concentration, voltage ranges, electrode materials…). In this thesis, only a few different electrolytes were tested and will be presented later.

This chapter represents the experimental section of this manuscript. Its purpose is to explain the sample preparation for the electrochemical and structural characterizations of the NaxMO2 phases studied in this thesis. Some explanations are also given concerning the electrochemical cycling curves.

Experimental devices used for structural characterizations are also presented. The synthesis method used to obtain the NaxMO2 phases studied in this thesis is described at the beginning of each part dedicated to a system. PTFE cannot be used in electrodes prepared to study the structure of the materials as it requires dispersed powder. Therefore, the electrodes consist in a mixture of active material and carbon black in a 80 : 20 weight ratio (total mass ≈ 80mg). Once ground, the mixture is pressed into a pellet (∅ 10 mm, 4

II.1. Electrochemical characterizations

tons pressure) to facilitate the handling of the electrode and increase its electrical conductivity.

II.1.b. Assembly of a Na battery

The characterization of the positive electrode materials studied in this manuscript requested the assembly of Na batteries under argon atmosphere in a glovebox. At the laboratory scale, two systems referred as Swagelok™-type and coin cell are commonly used. After assembling they are plugged to a Biologic VMP3 potentiostat in order to perform the electrochemical characterizations.

-45-

The Swagelok™-type cell

The Swagelok™-type cells are named after the Swagelok™ Company, specialized in the manufacturing of tube, valves … for gas and fluid systems. As the materials involved in the battery are very air sensitive, their products were used as battery containers. Nevertheless, the first electrochemical cells following a similar blueprint were used before the apparition of this name and are still in use in our laboratory. A representation and picture of the Swagelok™-type system is given in Concerning this work, the Swagelok-type cells were mostly used for the preparation of materials through a Potentiostatic route or for short electrochemical characterizations.

The 2032 coin cell

The coin cell batteries are similar to the ones available commercially. The assembly of a Na battery in these containers is similar to the one previously described. As shown in Figure II.2, the positive electrode is in contact with the current collector and separated from the negative electrode by 3 layers of separator.

However, the Na foil is now deposited on a stainless support and separated by a stainless steel spring from the negative current collector in order to maintain the pressure while assuring the electrical contact. A joint prevents the apparition of short circuits resulting from the contact between the two current collectors and ensure the airtightness of the cell once sealed using a manual press inside the glovebox.

Pictures of an assembled cell are given in

II.2. Structural characterizations

II.2.a. Laboratory and synchrotron X-Ray powder diffraction (XRPD)

As for most of their NaxMO2 homologues, the Nax(Mn,Fe)O2 and NaxNiO2 materials are very sensitive to air and moisture. Therefore, it is necessary to manipulate the samples in Argon filled glove boxes and to confine them into airtight systems in order to characterize them. It is possible thanks to specifically designed cells (laboratory XRPD) and capillaries (laboratory and synchrotron XRPD).

Every refinement of the structures from the diffraction patterns (X-Rays, Neutron or synchrotron) was realized using the Jana2006 software [101]. The absorption correction factor was systematically used

Ex situ XRPD in airtight sample holders

For these measurements, the powders are first sifted through a 40 µm sieve to ensure a homogeneous distribution of the particle sizes. The sifted powder is then deposited on the diffraction plane of the airtight sample holder using a razor blade, in order to prevent preferred orientation of the NaxMO2 particles due to their plate-like shape. The airtightness is maintained through the use of a polyimide window which is transparent to X-rays for 2θ > 10°. To ensure that the sample is not exposed to air during long measurements (12h), a small piece of metallic sodium acting as a getter is added in the cell, outside of the diffraction beam path: due to the higher sensitivity the sodium has to oxygen and water, if a small quantity of air was to enter the cell, it would react with the sodium instead of the powder. This technique allowed us to get good quality XRPD patterns using the Cu kα1,2 radiation (collaboration with E.

Lebraud, Engineer at ICMCB). A graphite (002) monochromator was used to suppress the fluorescent signal due to the iron specie in the NaxMn1-yFeyO2 samples. The measurements were carried out in the 10 -120

° range and the Lebail or Rietveld refinements were performed in the same ranges. The 2θ ranges presented in this manuscript may differ for clarity purposes.

Ex situ XRPD and Synchrotron XRPD in glass and polyimide capillaries

As for the previously described measurements, the powders are sifted to ensure that the size of the agglomerates is lower than 40 µm. The powders are then loaded into capillaries whose nature and diameter will depend on the analyzed material and the diffraction technique apparatus, as presented in the following -51--Concerning XRPD, the glass capillaries diameter was impacted by the analyzed material. A 0.3 mm capillary is an optimum for the NaxNiO2 material as it offers the possibility to use more powder and to get a better signal/noise ratio. On the contrary, the presence of iron in the Nax(Mn,Fe)O2 material lead to a fluorescence problem, as the diffractometer is not equipped with a monochromator. Therefore, a minor powder quantity coupled to a higher counting time was required to get a better XRPD pattern. At the laboratory scale, the capillary system offers the advantages of using a small quantity of powder and to conserve the samples as the capillaries were filled under Ar and sealed using a flame. It was the technique chosen to confirm the materials purity before running a Synchrotron XRPD pattern.

-Concerning SXRPD, the capillaries were filled under argon and sealed in the glovebox using epoxy glue, whatever their nature. Glass capillaries were used at former ID 31 beamline at the European Synchrotron Research Facility (ESRF, Grenoble, France) in collaboration with Dr. C. Drathen and polyimide capillaries were used at 11-BM beamline at the Advanced Photon Source (APS, Argonne National Laboratory, Argonne, IL, USA) in collaboration with Dr. M. Suchomel. The advantage of the polyimide capillaries is their flexibility that facilitates their handling within the glovebox.

For the refinements associated to the capillary setup, we considered a 50% packing of the powder into the capillaries to evaluate the absorption correction factor.

In situ XRPD during electrochemical cycling

In situ XRPD coupled to electrochemical cycling of a specifically designed cell is a powerful tool to investigate a phase diagram as it was already shown for other NaxMO2 material [48, 54-56, 70, 72]. The positive electrode current collector consists in a beryllium window, which is transparent to X-Rays and only shows two main diffraction peaks for 2θ > 45°. The cell is simultaneously placed in the diffractometer and plugged to a potentiostat to control and record the electrochemical part of the experiment (galvanostatic cycling, measure of the electrochemical variable…). The positive electrode was made from an Active Material / Carbon black / PTFE as described in the Electrode preparation section. Two types of experiments were carried out:

-In situ XRPD at the equilibrium. This method is the most commonly used for in situ XRPD. The battery follows a GITT cycling protocol, altering (dis)charge and relaxation steps. At the end of the relaxation period an XRPD pattern is recorded when the voltage shows no important variation. This technique characterizes the material in its relaxed state and the obtained XRPD pattern corresponds to a precise Na content in the material. It is therefore the best choice to observe Na/vacancies orderings and other peculiar compositions. To better separate close diffraction -52-peaks, we carried out these experiments using a diffractometer equipped with a germanium (111) monochromator in order to only use the Cu kα1 incident radiation (λ = 1.54056 Å).

-Operando in situ XRPD. This method is commonly used at user facilities such as synchrotron and neutron facilities in which the available time is limited. The battery is continuously (dis)charged and the XRPD measurement is carried out in the same time. Therefore, there is a difference in the sodium content between the beginning and the end of each XRPD pattern. It requires optimizing the conditions to get a good data quality corresponding to a small x range. This technique is the best choice to characterize a battery in real cycling conditions and a quick option to characterize materials with no peculiar compositions.

Two different cells were used depending on the diffractometer manufacturer and are represented in The assembly of the Panalytical cell is similar to the one of the coin cell-type battery. On the contrary, the assembly of the Bruker cell is similar to the one of the Swagelok™-type cell. This model was developed in LRCS (Amiens, France) [104]. The gamma photon has then to be absorbed (rezoning absorption) by a stable nucleus of similar nature (absorber) which will get excited (Figure II.7b). As the absorption and emission of gamma photons are very energetic phenomenon, both the Mössbauer source and absorber have to be bounded in the solid state of their respective matrixes/amorphous lattices/crystal lattices, in order to avoid any energy loss due to recoil. As for every spectroscopy technique, it is necessary to scan a sufficient energy range. As the Mössbauer source emits a monochromatic radiation, varying the energy is achieved using the Doppler effect, moving the Mössbauer source while keeping the absorber still. The detector records the transmitted beam as a function of the velocity. This results in a Mössbauer spectrum, represented in Figure

II.2.b. 57 Fe Mössbauer spectroscopy

II.8.

All measurements in the present work were performed at room temperature with a constant acceleration Halder -type spectrometer using a 57 Co source (Rh matrix) in transmission geometry. The chemical shift: δ

The chemical shift δ is expressed in mm.s -1 and corresponds to the shift of the absorption maxima to the origin (0 mm.s -1 ) given by a reference (usually Fe α). It is a consequence of the resonance energy of the nucleus which is impacted by the transition of the electrons on its s orbital. Depending on the s electron charge density, the spectrum can be shifted in a positive or in a negative direction. For a multiplet, the chemical shift is given by the position of the barycenter of the different peaks, as shown in (2) The electronic repartition of the charges around the nucleus must be non-spherical, creating an electric field gradient. The electric field gradient is impacted by (i) the ions surrounding the probed atom or (ii) the valence electrons of the probed atom, the latter being the most important. In the case of the HS-Fe 3+ ion (3d 5 ) in an octahedral coordination, the valence electrons are evenly distributed and thus only the surrounding ions will impact the electric field gradient.

The interaction between the electric quadrupole moment and the electric field gradient(s) will then lift the degeneracy of the nuclear states, as represented in Figure II.9 for an excited 57 Fe atom: the 3/2 → 1/2 transition is divided into two sub-states: mI = ± 1/2 and mI = ± 3/2, creating as many peaks on the spectrum, which will correspond to a doublet. Concerning the Fe 3+ and Fe 4+ ions, the quadrupole splitting gives precious information on the deformation of the site and on the cationic distribution around it.

The magnetic splitting (also hyperfine splitting or Zeeman effect)

The magnetic splitting is the result of the interactions between the nuclei and any surrounding magnetic field. As for the quadrupole splitting, the resulting spectrum will consist in a multiplet, generally a sextet. The exploitation of the spectrum gives precious information on the magnetic interactions. In this work no measurement was performed on magnetically ordered materials. This calculation requires fixing a reasonable value for the FWHM (typically between 0.20 and 0.30 mm.s -

I

1

). An average value of the quadrupole splitting (Δ*) is refined along with the populations associated to the various Mössbauer sites.

Experimental: in situ 57 Fe Mössbauer spectroscopy

Due to the severe regulations concerning the use of radioactive materials, all the measurements have to be done by habilitated people. At ICMCB, measurements were performed by A. Wattiaux, Research Engineer and S. Bordère, Researcher. The Mössbauer spectra were recorded at RT with a constant acceleration Halder -type spectrometer using a 57 Co source (Rh matrix) in the transmission geometry. The velocity was calibrated using pure iron metal as the standard material, which also corresponds to the reference of the spectra.

To follow the evolution of the Mössbauer spectra during the cycling of a Na battery, we adapted an in situ cell previously used in our laboratory [START_REF] Rougier | Relation entre la structure et le comportement électrochimique des phases LixNi1-yMyO2 (M = Al, Fe, Co) : Matériaux d'électrodes positives pour batteries au lithium[END_REF] in collaboration with D. Filimonov 6 , Invited Professor.

The main challenge consisted in the selection of the materials constituting the cell which must not contain iron traces or absorb the signal if in the beam path. Therefore, aluminum, copper and stainless steel were 20 ratio, with a total mass of ≈ 100 mg (i.e. ≈ 3 mg Fe per cm² for the NaxMn1/3Fe2/3O2 system). Due to the long measurement time (48 h) requested for each spectrum, we followed a similar protocol to the one described in the potentiostatic synthesis section: the battery was first discharged and the voltage was 6 Lomonosov Moscow State University, Russia -57-maintained for several days to ensure a stable current response. After a preliminary measurement, the cell was charged at C/100 until the next targeted voltage which was maintained for two days. The spectrum was then recorded during the following 48 hours under constant voltage of the cell. These two steps were repeated for all the targeted voltages/sodium contents.

II.2.c. X-ray absorption spectroscopy

X-ray absorption spectroscopy or XAS is a commonly used technique at user facilities which allows the determination of local structures and oxidation state. It is based on the excitation of the core-level electrons of an atom (K, L or M shells) when it is exposed to X-rays of specific energy (edge) equal to the energy difference between the excited and fundamental electronic states. This phenomenon is the basis of photoelectric absorption. The absorption A of the X-ray beam through a slab is proportional to the ratio between the intensities of the incident and transmitted X-ray beams. It is also calculated from the absorption coefficient of the cross-section µa, as represented in

X-ray Absorption Near Edge Structure: XANES

The X-ray absorption near edge spectroscopy or XANES part of the spectrum contains information on the oxidation state and coordination environment of the absorbing atom. In our materials, XANES was only used to confirm the oxidation state of the absorbing atoms and required the analysis of several reference compounds (Mn III 2O3 and Li2Mn IV O3 for the Mn K-edge for example).

Extended X-ray Absorption Fine Structure: EXAFS

The extended X-ray absorption fine structure or EXAFS part of the spectrum contains information on the surrounding neighbors of the absorbing atom. The cell consisted in a coin cell battery similar to the one presented at the beginning of this chapter. The positive and negative current collectors were drilled in the center and recovered with polyimide tape. In order to maintain the electronic conductivity, a thin aluminum foil transparent to X-ray was used. The second difference to the previously discussed coin cells comes from the liquid electrolyte which is obtained by dissolving NaPF6 into a mixture of EC and DEC (1 : 1 volume ratio, final concentration of 1 mol.l -1 ).

All data refinements were carried out at NTUST by Cheng Ju-Hsiang as they required an important knowledge of X-ray Absorption Spectroscopy and of the corresponding softwares.

II.2.d. Chemical analysis

The Na / M and the Mn / Fe ratios of the various materials were verified by chemical analysis using an optical emission spectrometer equipped with an Inductively Coupled Plasma (ICP) source. The ionization of an argon flux creates a hot plasma (6000 K -10000 K) that will vaporize the dissolved sample into unbound atoms and excited ions. While coming back to their fundamental state, these atoms and ions will emit ultraviolet and visible photons. A photomultiplier counts the photons and the comparison to a series of reference samples will allow the quantification. In our materials, only the Ni, Fe, Mn and Na cations could be quantified. The samples were prepared by dissolving 10 mg of powder into boiling aqua regalia (HCl : HNO3 mixture in a 1 : 2 ratio). Three measures were realized for each sample on a Varian 720ES apparatus by L. Etienne, Engineer at ICMCB. The first part of the present work focuses on the NaxMn1-yFeyO2 materials (y = 1/3, 1/2 and 2/3).

In this first chapter, an extended bibliographic study is presented along with the motivations that drove us to study this particular system among NaxMO2 layered oxides. The synthesis of the pristine materials is first described before we present their structural and morphological characterizations. Last, we present the first electrochemical characterizations of the different materials.

A-I.1. The NaxMn1-yFeyO2 layered oxides in the literature

The first study on the Nax(Fe,Mn)O2 system was realized during Parant's Ph.D. thesis defended in 1970 in Bordeaux [START_REF] Parant | Sur quelques nouveaux oxydes ternaires du système manganèse -oxygène -sodium[END_REF]. His aim was to study the phase diagram in the MnO2 -NaFeO2 system: The NaxFexMn1-xO2 phase diagram. Depending on the x value, several structural domains were isolated, including a pure O3 domain for 0.7 ≤ x ≤ 1.0 and a pure P2 domain for 0.45 ≤ x ≤ 0.55. As these materials did not show any interesting physical properties, no other study was reported before 2003 when Matsumura et al. reported the synthesis of P2-Na2/3Mn1/3Fe2/3O2 (+ Fe2O3 impurity) as an intermediate for the preparation of new Li-ion positive electrode materials after a Na + ↔ Li + ionic exchange [65].

The reinvestigation of the P2 systems started at ICMCB by Dr. D. Carlier and Dr. C. Delmas in 2010 in collaboration with Pr. R. Stoyanova 7 . This work was the starting point of my Ph.D. Simultaneously to this Ph.D., several papers were published. The use of NaxFe1-yMnyO2 materials as positive electrode materials in Na batteries was first mentioned in 2011 by Yabuuchi et al. [START_REF] Yabuuchi | th ECS Meeting Abstract #[END_REF]. They reported the solid state synthesis and the charge/discharge profiles of the P2-Na2/3Mn2/3Fe1/3O2 and O3-Na1Mn1/3Fe2/3O2 phases. The huge leap in the publication number concerning this system started in April 2012 when the same authors reported the structural and electrochemical properties of the P2-Na2/3Mn1/2Fe1/2O2 and O3-Na1Mn1/2Fe1/2O2 phases in Nature Materials [26]. These materials showed second cycle discharge capacities of 190 mAh.g -1 and ≈ 110 mAh.g -1 for the P2 and O3 phases respectively when cycled between 1.5 and 4.3 V at C/20. In the following months, Yoncheva et al. reported the synthesis of P'3-Na2/3Mn1-yFeyO2 phases (y = 0; 1/3; 2/3) in collaboration with ICMCB [27]. The NaxMn1-xFexO2 phase diagram (0.5 ≤ x ≤ 1.0) and its electrochemical properties were reinvestigated by Thorne et al. in 2013 who obtained similar results on the P2-Na0.5Mn1/2Fe1/2O2 phase than those from Yabuuchi et al. [28]. In 2014, Zhao et al. published the first study focusing on the P2-Na2/3Mn2/3Fe1/3O2 phase and investigated the electrochemical and thermal properties of this material [32]. They obtained an interesting second discharge capacity of 193 mAh.g -1 while cycling the corresponding Na cell into the 1.5 -4.3 V range at C/20. 7 Bulgarian Academy of Sciences, Institute of general and Inorganic Chemistry, Bulgaria.

-67-Despite the interesting discharge capacities of the P2-NaxMn1-yFeyO2 materials, an important drawback is that the starting material represents an intermediate state of intercalation. This is a problem for Na-ion batteries as it requires an over-sodiated negative electrode. To overcome this issue, Singh et al.

suggested adding 5 % of NaN3 into the electrode preparation [29]. This Na source decomposes during the cycling to compensate the lack of Na into the starting material. However it releases gaseous N2 into the battery increasing the pressure of the system which can lead to safety issues.

In all the studies reported in the literature, P2 and O3-NaxMn1-yFeyO2 materials are prepared by a solid state chemistry synthesis, involving a Na precursor (Na2CO3 [28,29,65] or Na2O/Na2O2 [26,28,33] mixed with Fe (Fe2O3 [26,29,32,33] or Fe3O4 [28,65]) and Mn (Mn2O3 [26,29,32,65] or MnO2 [28,33]) oxides. The mixture is then heated under air or O2 for 12 -36 hours with [28,33] or without [26,27,29,32, 65] a previous ball milling step.

A-I.2. Synthesis of the pristine materials

A-I.2.a. The aqueous self-combustion type synthesis

When we started the study of the NaxMn1-yFeyO2 phase diagram, only Parant's thesis and Matsumura et al.'s work on the P2-Na2/3Mn1/3Fe2/3O2 phase were published [65,[START_REF] Parant | Sur quelques nouveaux oxydes ternaires du système manganèse -oxygène -sodium[END_REF]. At ICMCB, the P2-Na2/3Mn2/3Fe1/3O2 phase was studied by Dr. M. Yoncheva (Invited researcher) in 2010 and by Dr. T Okamura (Invited Post-doctorant) in 2011. Their materials were prepared by co-precipitation and classic solid state synthesis routes, respectively.

The first goal of this thesis was to synthesize other NaxMn1-yFeyO2 materials. Mn / Fe ratios of 1 / 1 (NaxMn1/2Fe1/2O2) and 1 / 2 (NaxMn1/3Fe2/3O2) were targeted. Unfortunately, our attempts to synthesize materials with new Mn / Fe ratios based on the existing protocols were not successful. Therefore, we tried the self-combustion synthesis route (or smoldering combustion synthesis). This synthesis route consists in a redox reaction between an oxidizer and a fuel. The oxidizer (oxidizing agent) usually consists in transition metal and/or alkali nitrates (LiNO3, NaNO3, M 3+ (NO3-)3, M 2+ (NO3-)2…). The fuel represents the reducing and chelating agent of the reaction. Glycine (H2N-CH2-COOH) represents one of the most used fuels for self-combustion type syntheses [109]. When the solution is heated, the reaction occurs following two steps: 1) Glycine undergoes polycondensation according to (A-I.1):

+ H3N-CH2-COO -+ + H3N-CH2-COO -→ + H3N-CH2-CO-NH-CH2-COO -+ H2O (A-1.1)
2) The redox reaction occurs according to (A-I. As one can see depending on the oxidizer / fuel ratio (α in (A-I.2)) the reaction will necessitate an external source of oxygen (air). This oxidizer / fuel ratio is a key parameter of the reaction as it also influences the flame temperature reached during the reaction (typically above 1000°C [109,110]). Selfcombustion syntheses result in the obtention of a homogeneous, small-sized precursor or poorly crystallized phase [111]. Using self-combustion type synthesis, our idea was to prepare a precursor with a good distribution between Fe and Mn.

A-I.2.b. Synthesis of the pristine materials

Following a self-combustion synthesis protocol, the NaxMn1-yFeyO2 materials are synthesized by dissolving manganese, iron and sodium nitrates (Alfa Aesar Mn(NO3)2.4H2O (97% purity), Fe(NO3)3.9H2O (98%) and NaNO3 (99%) respectively) into water. The final concentration of the Mn and Fe solutions is 1 mol.l -1 . A 10 wt % excess of NaNO3 is added to take into account the high volatility of sodium oxide. After total dissolution, glycine (Sigma-Aldrich, ≥ 99%) is added. After a few attempts, we chose the molar NO 3-/ glycine ratio (oxidizer / fuel) equal to 8 / 1 in order to lower the temperature and violence of the reaction.

A dark brown coloration occurs in the solution, resulting from the complexation between the Fe 3+ ions and glycine [START_REF] Djurdjevic | Transition Met[END_REF]. The complexation is also expected to affect the Mn 2+ ions. The solution is then poured into a ceramic bowl and placed into a sand bath heated at 480°C on a hot plate for several hours. Once the combustion is complete, a fine black powder is obtained after grinding, as shown in The combustion product is then heated in a gold boat in a tubular furnace, first at 700 °C for 20 h under air to allow the chemical reaction between NaNO3 and the Mn1-yFeyO3 precursor. A second heat treatment performed at 1000 °C for 5 h under O2 is then applied to better crystallize the material. The heating ramps are equal to +5°C.min -1 . A graphical representation of the heat treatment step is given in -70-After the heat treatment, the samples are quenched down to room temperature and stored into an Ar filled glovebox to avoid reaction with moisture. The targeted mass of final product is 5 g.

A-I.2.c. Investigation of the NaxMn1-yFeyO2 phase diagrams by self-combustion synthesis

All materials show the same tendency when increasing the Na / (Mn + Fe) ratio while keeping the Mn / Fe one constant: for the lowest sodium ratios (xNa ≈ 0.6) a P2 + Fe2O3 phase domain is observed, followed by several others upon increase of the sodium content: P2, P2 + O3, O3 and finally O3 + O'3.

Depending on the Mn / Fe ratio the limits of pure phase domains vary. We therefore studied the NaxMn2/3Fe1/3O2, NaxMn1/2Fe1/2O2 and NaxMn1/3Fe2/3O2 phase diagrams for 0.6 ≤ x ≤ 1.0, with a theoretical sodium variation of 0.025 Na + per formula unit. The synthesis protocol is similar to the first one we described; however we targeted 2 g of final product for each sample. The XRPD measurements were carried out in the selected 15.5° -16.5° and 31° -40° 2θ ranges (Cu kα1,2) in 0. (1) High Mn contents stabilize P2-type structures. Indeed, a pure P2 phase domain is observed for 0.6 ≤ x ≤ 0.8 for the NaxMn2/3Fe1/3O2 system, while it is observed between 0.675 ≤ x ≤ 0.775 for the NaxMn1/2Fe1/2O2 one. No pure P2 phase was obtained for the NaxMn1/3Fe2/3O2 phase system, in agreement with Matsumura et al. [65].

(2) On the contrary, high Fe contents stabilize O3-type structures and pure O3 phases were obtained starting x = 0.775 (theoretical Na : M ratio) in the NaxMn1/3Fe2/3O2 system. Only an O3 + O'3 phase domain was obtained in the NaxMn1/2Fe1/2O2 system and no pure O3 phase domain was evidenced in the NaxMn2/3Fe1/3O2 system. However, several studies report the existence of pure O'3-NaMnO2 phase [5,44] suggesting that a Fe substitution in this material would be possible. Our failure in obtaining a pure O'3 or O3-NaxMn2/3Fe1/3O2 phases could be induced by our synthesis route.

Following the same reasoning, it must be noted that almost-pure O3-NaMn1/2Fe1/2O2 was obtained by Yabuuchi et al. by direct solid state synthesis, but shows traces of P2-NaxMn1/2Fe1/2O2 and Na3MnO4 [26].

According to (1) and ( 2), increasing the Mn (Fe) contents will stabilize the P2 (O3) phases on a wider Na range.

We then targeted the structure types by controlling the sodium content: the P2-Na0.77Mn2/3Fe1/3O2, the P2-Na0.67Mn1/2Fe1/2O2, the (O3+O'3)-Na0.82Mn1/2Fe1/2O2 and the O3-Na0.82Mn1/3Fe2/3O2 phases.

A-I.3. Characterization of the pristine materials

A-I.3.a. X-ray powder diffraction analysis

The XRPD patterns corresponding to the targeted materials are shown in -73-

The P2 and O3 phases crystallize in the hexagonal (P63/mmc) and the rhombohedral (R-3m) systems, respectively. The cell parameters of the different materials are very close to those reported in the literature for the same Mn / Fe ratios [26][27][28][29]32]. As expected from the various stacking, a larger interslab distance is observed in P2-type structures than in O3-type ones, in agreement with the larger size of the prismatic sites compared to the octahedral ones.

We attribute the existence of the O'3 phase in the (O3+O'3)-Na0.82Mn1/2Fe1/2O2 mixture to the cooperative Jahn Teller effect of the Mn 3+ ions as suggest the amon./bmon. = 1.77 ratio. We then expect the O'3 phase to have higher Mn 3+ content -i.e. higher sodium content-than the O3 one if the Mn / Fe ratio is constant. It also possible that two materials with slightly different Mn / Fe ratios coexist in the (O3+O'3)-Na0.82Mn1/2Fe1/2O2 mixture.

For every batch of material, the ICP-AES analysis confirms the Mn / Fe and Na / (Mn + Fe) ratios.

The theoretical and experimental ratios are compared to the one determined by the Rietveld refinement on the structures from the synchrotron XRPD patterns in Na vaporized during the synthesis and/or the heat treatment step. However, the Na contents deduced from the Rietveld refinement of the different materials conducted to lower Na contents. We suppose that a significant part of the Na + ions were vaporized from the material, probably during the air quenching step, creating Na2CO3 and NaOH at the surface of the material. The sodium contents determined by the Rietveld refinements would therefore give a better estimation of the amount of the intercalated Na + ions and will be considered.

A-I.3.b. Morphology

The different P2 and O3 phases were analyzed by Scanning Electron Microscopy to determine their morphology. It appears that the material with the P2-type structure exhibits well-shaped particles of 3.4 μm average diameter and 200 nm thicknesses. The hexagonal plate-shaped particle morphology is similar to other P2-type phases [61,88,91]. The O3-type phases show round-shaped particles of 3 μm average size.

The small imperfections on the surface of both materials are due to air exposition during the sample handling prior to the gold sputtering. The impurity amount increased both in number and size with the air exposure time. We believe it corresponds to NaOH /Na2CO3 impurities which are formed on the surface as sodium leaves the material, allowing the average Mn oxidation state to increase. All phases present agglomerated particles with larger sizes than the ones reported by Yabuuchi et al. (500 nm mean size) [26]. This is certainly related to the higher synthesis temperature of our materials (1000°C vs. 700-900°C [26]).

A-I.3.c.Electrochemistry

To confirm the electrochemical activity of the various materials, we prepared Na-cells involving the NaxMn1-yFeyO2 phases as active materials.

Optimization of the liquid electrolyte

First, we investigated the influence of electrolyte additives in order to optimize the cycling properties, using an upper cutoff voltage of 3.8 V. The role of fluoroethylene carbonate (FEC) on the prevention of the electrolyte was recently studied by Komaba et al. [99] while vinyldiene carbonate (VC) is a well-known additive used for Li-ion batteries electrolytes [98]. As one can see, the use of 2 wt% of VC or FEC additives in the electrolyte clearly prevents the electrolyte decomposition in the 1.5 -3.8 V voltage window, leading to a better overlap of the cycling curves and to better capacity retention. A discharge capacity of ≈ 132 mAh.g -1 is reached on the second cycle in this voltage range and the capacity retention is equal to 92 % at the 12 th cycle. After further cycling, the behavior strongly depends on the electrolyte used: without additive (in blue) a sudden decrease of the capacity is observed. Thanks to the use of additives, the capacity fading is reduced. Among the two additives considered, FEC leads to slightly better results than VC and was then further used for our studies.

In the literature, the FEC additive was also shown to play a key role in preventing the electrolyte decomposition: without any additive the propylene carbonate solvent reacts with the Na foil constituting the negative electrode, the resulting reductive decomposition forming sodium propyl carbonate [99].

Galvanostatic cycling between 1.5 and 3.8 V

All the NaxMn1-yFeyO2 phases were then tested as positive electrode materials in Na batteries involving the NaPF6 in PC (1 M) + 2 wt% FEC electrolyte. 3, the plateau is slightly higher in voltage for the O3 phases than for the P2 ones (≈ 0.2 V). This indicates that a higher energy is required to (de)insert the Na + ions from the inter-layer space in the O3 stacking. The lower polarization of the P2-type structures suggests an easier diffusion path than for the O3-type structures, as evidenced in the P2 and O3-NaxVO2 phases [START_REF] Didier | Etude des oxydes lamellaires NaxVO2 : électrochimie, structure et propriétés physiques[END_REF]. Concerning the (O3+O'3)-Na0.77Mn1/2Fe1/2O2 phase, one can see that the starting point (inset of Figure A-I.8c) is located on the voltage plateau. We assume that this plateau is characterized by equilibrium between the O3 and O'3 stacking types and that the intercalated state of the O3 materials corresponds to an O'3 structure. By analogy, different structures derived from the P2-type are also expected for the intercalated P2 phases.

Formula of the starting material

Voltage of the voltage plateau (V)

1 st discharge 1 st charge P2-Na0.66Mn2/3Fe1/3O2 2.08 V 2.21 V P2-Na0.62Mn1/2Fe1/2O2 2.08 V 2.17 V (O3+O'3)-Na0.77Mn1/2Fe1/2O2 2.25 V 2.40 V O3-Na0.77Mn1/3Fe2/3O2 2.25 V 2.40 V Table A-I.3:
Values of the voltage plateaus associated to the first discharge and first charge for the different NaxMn1-yFeyO2 materials.

Upon further deintercalation, the E = f(x) curves exhibit a solid solution behavior and undergo a sudden voltage jump at x ≈ yFe for the materials with Mn / Fe ratios equal to 1 / 1 and 1 / 2. These voltage jumps may correspond to a change of redox process from Mn 3+ → Mn 4+ to Fe 3+ → Fe 4+ as already shown in the literature by X-Ray Absorption Spectroscopy and Mössbauer Spectroscopy [26,28]. If for the P2 phases the first discharge is similar to the others, one can notice an important increase of the polarization for the E = f(x) curves associated to the O3 materials in the Mn 4+ /Mn 3+ redox couple activity range while the polarization decreases in the Fe 4+ /Fe 3+ one. Comparing the second discharge capacities, one can see that the battery assembled from P2-Na0.66Mn2/3Fe1/3O2 reach the highest value (144 mAh.g -1 ). Decreasing the Mn content in the P2 structures lowers this capacity to 133 mAh.g -1 for the NaxMn1/2Fe1/2O2 composition. On the contrary, decreasing the Mn content increases the second discharge capacity for the O3 structures and 132 mAh.g -1 are available for the NaxMn1/3Fe2/3O2 composition vs. 124 mAh.g -1 for the and NaxMn1/2Fe1/2O2 one. In average, the discharge capacity of the batteries prepared with P2-type materials at the positive electrode is higher, following the general trend mentioned in the introduction.

Looking at the 20 th cycle discharge capacity retentions, all phases exhibit similar values: 91 % (P2-NaxMn2/3Fe1/3O2), 93 % (P2-NaxMn1/2Fe1/2O2), 91 % (O3-NaxMn1/2Fe1/2O2) and 89 % (O3-NaxMn1/3Fe2/3O2).

Despite it exhibits a higher second discharge capacity; the NaxMn1/3Fe2/3O2 composition shows worse capacity retention than the NaxMn1/2Fe1/2O2 one among the O3 structures. Furthermore, comparing the two NaxMn1/2Fe1/2O2 materials, the P2-type one show slightly better stability.

By comparison to the literature, P2-Na0.62Mn1/2Fe1/2O2 exhibits a lower second discharge capacity than the one reported by Yabuuchi et al [26]: 133 mAh.g -1 vs. 190 mAh.g -1 . This difference is explained by the lower voltage limitation of our study (3.8 V vs. 4.3 V).

)

-79-It is thus surprising that the second discharge capacities of our O3-NaxMn1/2Fe1/2O2 and O3-NaxMn1/3Fe2/3O2 phases are higher than the ones reported by Yabuuchi et al. (124 mAh.g -1 vs. ≈ 110 mAh.g -1 respectively for O3-NaxMn1/2Fe1/2O2 and ≈ 132 mAh.g -1 vs. 90 mAh.g -1 respectively for O3-NaxMn1/3Fe2/3O2). These differences could come from the different preparation conditions, as we prepared O3 phases with an initial Na amount lower than one (vs. one in [26,[START_REF] Yabuuchi | th ECS Meeting Abstract #[END_REF]) and a 1000°C final heat treatment under O2 atmosphere (vs. 700°C in air in [26]). Furthermore, these systems could present transition metal vacancies in the slab thus stabilizing more Mn 4+ ions as expected from the ideal formula. Such transition metal vacancies were already observed in P'2-NaxMnO2 phases [5,52,[START_REF] Stoyanova | [END_REF]. In this hypothesis, the formula of the materials should be rewrote as Na2x/(2+y)(Mn,Fe)2/(2+y)□y/(2+y)O2. the Na + ion into the interslab space and is not uncommon in these materials [79,94,115]. The final sodium content determined by Synchrotron XRPD (x = 0.77 (1)) is lower than the theoretical one (x = 0.82) and the one of the formula determined by ICP-AES analysis (Na0.83Mn0.31Fe0.69O2). This indicates that a small portion of the Na + ions were expelled from the material, probably during the air quenching step or by reaction with the oxygen and water in the glovebox as discussed in Chapter A-I. Note that the occupancy of the O site was fixed to 1.0, thus only the corresponding ADP value is refined and is equal to 0.75(8) Ų. In the latter, this material will be referred to as O3-Na0.77Mn1/3Fe2/3O2.

Previous works on Mn-based alkali layered oxides showed the possibility of transition metal vacancies due to the spontaneous oxidation of Mn 3+ according to the reaction: 4 Mn 3+ 3 Mn 4+ + [5,52,[START_REF] Stoyanova | [END_REF]. We considered this possibility and refined the occupancy of the transition metal sites in our material. However this did not lead to a significant improvement of the refinement as the occupation of the transition metal sites did not deviate significantly from 1.0. In the following, the O3-Na0.77Mn1/3Fe2/3O2 formula will be considered for the pristine material. If one assumes that iron is trivalent, there is 0.23 Mn 4+ and 0.10 Mn 3+ per formula unit.

Neutron powder diffraction

Because of the presence of Mn 3+/4+ and Fe 3+ ions in the 1:2 ratio, we considered the possibility of an ordering within the transition metal layer even if the difference in ionic radii (Mn 3+ (r = 0.58 Å), Mn 4+

(r = 0.53 Å), Fe 3+ (r = 0.63 Å)) is not very large. The material was studied by neutron diffraction on the D2B beamline at ILL 9 . Contrarily to XRPD, neutron diffraction allows distinguishing Fe from Mn thanks to the very different Fermi lengths (equal to -3.73 fm and +9.93 fm for the 55 Mn (100 % abundance) and 56 Fe (91.75 % abundance) nuclei, respectively).

The neutron powder diffraction pattern of the pristine material is shown in

(006) (003)
(105) (009) (107) (108) (110) ( (101) (102) (104)
) (003) (006) (101) (102) 113
(105) (009)

(107) (108) (110) (113) a) b)
Intensity (A. U.)

A-II.1.b. Electrochemistry

Influence of the cut-off voltage

After confirming the electrochemical activity of the material (Chapter A-I.

V (Figures A-II.4g-h).

The SEM micrographs of the un-cycled electrode are representative of the raw material with monolithic grains. On the contrary, the micrographs collected after 50 cycles up to 3.8 V, 4.0 V or 4.3 V highlight the cracking of the material. However, the capacity decay occurring after a few cycles at high voltage cannot be explained by dramatic changes of the microstructure. -88-

GITT cycling

For a better understanding of the electrochemical behavior of the NaxMn1/3Fe2/3O2 system, a Galvanostatic Intermittent Titration Technique (GITT) experiment was performed as shown in Starting with a discharge from x = 0.77, the material exhibits a reversible plateau at low voltage for 0.85 ≤ x < 0.92 corresponding to a biphasic domain. Upon charging and after the voltage plateau (x < 0.85), the voltage continuously increases and overcomes a sudden jump at x ≈ 0.67. This voltage jump seems to correspond to the change in the active redox process: from Mn 3+ → Mn 4+ to Fe 3+ → Fe 4+ . During further charging (0.4 < x < 0.65), the voltage slightly increases. One can observe a lower polarization in this range. Then, above 3.8 V (x ≈ 0.37), the curve describes a voltage plateau followed by a graduated increase of the polarization with the upper potential. This strongly suggests that a new and unknown reaction occurs at high voltage. Moreover, the (00l)O3 diffraction lines shift to higher angles upon sodium deintercalation, which indicates a strong decrease of the interslab distance. This unexpected result is reproducible and reversible if the battery is discharged. In order to check if this special behavior is related to an experiment carried out of equilibrium, another in situ study was performed during a GITT charge, where the XRPD patterns were recorded at the end of each relaxation step (dE/dt < 2.6 mV.h -1 ). The same behavior was also found and is

presented in Figure A-II.8.
Obviously, for x < 0.62, there is coexistence of two systems that are deintercalated simultaneously. This point will be further discussed in details.

From the cell parameters, it is possible to estimate the interslab distances, corresponding to chex. The XRPD pattern of the initial phase of the operando in situ XRPD experiment, Na0.96Mn1/3Fe2/3O2

(end of discharge), can be indexed in the monoclinic system (C2/m space group, O'3 structure). The monoclinic distortion of the cell is clearly emphasized by the splitting of the (012)hex. and (104)hex.

diffraction lines of the O3 structure to the (-111)mon. + (200)mon. and to the (-202)mon. + (111)mon. ones respectively. During Na + deintercalation from Na0.96Mn1/3Fe2/3O2, a very narrow composition domain is observed for the O'3 phase (0.94 < x < 0.96), followed by a biphasic domain (characterized by the voltage plateau), observed for 0.85 ≤ x ≤ 0.94. In this domain, the small number of diffraction peaks available to fit the profile prevents from giving a really accurate value of the cell parameters for the two phases.

Nevertheless, it appears that the interslab distance is slightly higher for the O3 phase than for the O'3 one. This is induced by the lower Na content in the O3 phase, which lowers the screening effect of the Na + ions on the surrounding O planes.

For 0.62 < x < 0.85 the system exhibits a solid solution with an O3 type structure as observed for the pristine material. The interslab distance increases as sodium is removed from the interlayer space, enhancing again the repulsion between the O atoms from the MO2 planes. On the contrary, the M-M in plane distance (ahex. parameter) decreases as the average ionic size of the M n+ ions decreases upon oxidation.

Upon Na + deintercalation a new phase with a P3 type structure appears for x < 0.62, while the intensity of the O3 phase diffraction lines decreases. As previously mentioned, a significant part of the O3 type phase remains. The position of its (003)O3 diffraction line continues to shift to lower 2θ angles down to x = 0.50 and then to higher 2θ angles for x < 0.50 (Figure A-II.10). The corresponding domain will be referred to as "O3*". This shift shows that the interslab distance increases upon deintercalation and then decreases at the end of the charge as it is observed for all O3 type AxMO2 (A = Li, Na) systems [116]. Note that in the LixCoO2 and LixNiO2 systems, the complete lithium deintercalation leads to the O1 type structure ("ABAB" packing) [117].

For x ≤ 0.16 a new phase, noted "X", is observed. Its (00l)X diffraction line shift continuously to higher 2θ angles upon deintercalation, indicating a decrease of the interslab distance. The position of the (003)P3 line remains constant between 0.56 < x < 0.62 as expected for a biphasic domain and then shifts to lower angles, which indicates the occurrence of a solid solution (0.39 < x < 0.56) also for the P3 type phase. This behavior is more clearly seen in Figure A-II.10 that shows the variation of the (003) line of both phases during the battery charge. In the 0.39 < x < 0.50 region, there is a two phases domain between two solid solutions (O3* and P3).

x in Na x Mn 1/3 Fe 2/3 O 2 2θ (°) Cu kα 1,2 E (V) (003) O3
When x decreases below 0.39 the position of the (003)P3 line remains constant while its intensity decreases. Simultaneously, a broadening appears on the high angle side, which suggests the formation of stacking faults within the P3 phase. One can make the hypothesis that when a too large number of sodium is deintercalated from P3, some MO2 slabs glide to create an octahedral surrounding for the remaining Na + ions. The P3 phase with stacking faults is noted P3* in the following. The number of this type of planes continuously increases when Na + ions are deintercalated from the material, in agreement with the shift of the (003)P3* diffraction line to lower 2θ angles.

For x = 0.16, the diffraction lines of the O3* and P3* phases have merged into a new phase, noted "X". Due to the relative sharpness and symmetry of the (00l)X diffraction line, we expect no stacking faults in the "X" phase. The same hypothesis (formation of the NaO6 octahedron environment for highly deintercalated phases) was primarily observed during operando in situ XRPD measurements by Lu and Dahn for the Na + deintercalation from P2-Na2/3Mn2/3Ni1/3O2, which leads to the O2 type structure [72]. The authors found an interslab distance equal to 4.32 Å, which is very similar to the NiO2 one [117]. The The simultaneous presence of two phases with the O3 and P3 structures type involved in the deintercalation process is difficult to understand. To explain it, we can make the hypothesis of composition fluctuations that are not detected in XRPD data of the starting material: (i) the coexistence of particles with slightly different Mn / Fe ratios or (ii) the existence of particles with or without Mn vacancies. It is well known that the relative stability of the O3 and P3 packing is directly correlated to the bond covalence within the slab and to the sodium amount [36]. In this hypothesis, a part of the O3 phase is going through deintercalation following a solid solution process while the other part is transformed into the P3 phase.

Further experiments are required to confirm this behavior.

To study the reversibility of the diverse structural transitions, we discharged the cell back to 1.5 V and recorded the XRPD pattern under constant voltage and with the same acquisition parameters. The XRPD patterns recorded after the first and second discharges are presented in Figure A-II.12. Surprisingly after the second discharge the monoclinic distortion is not observed. This is explained by the lower sodium content after the second discharge (x ≈ 0.8). The Mn 3+ content (≈ 13 % of the M n+ ions) is not enough to induce the cooperative Jahn-Teller effect. The lower sodium content intercalated implies that the material underwent an irreversible structural transition during the charge that may depend on the cycling conditions. The migration of Fe into the interlayer space can be considered, as suggested for NaxFeO2 [35]. -99-

Intensity (A.U.) 2θ (°) Cu kα 1,2 (002)
(-201) (-111) (200) (110) (-202) (111)

A-II.1.d. Ex situ Synchrotron X-ray diffraction study of the different structural domains

In order to better understand the structures of the various NaxMn1/3Fe2/3O2 phases, we prepared three samples (O'3, O3 and P3) by the potentiostatic route. A battery whose positive electrode consisted in a pellet of the active material and carbon black was (dis)charged to a desired voltage. Once reached, the voltage was maintained for several days in order to reach equilibrium. After washing and drying the electrode, a capillary was made to analyze the material by Synchrotron X-ray Powder Diffraction (SXRPD) 10 .

Materials prepared at a significantly higher voltage showed a loss of crystallinity and were not characterized by synchrotron XRPD.

The O'3-Na0.96Mn1/3Fe2/3O2 phase

The targeted voltage for the preparation of the O'3 material was 1.5 V (end of the first discharge on the E = f(x) curve). In order to correctly refine the profile of the peaks, we considered an anisotropic broadening through the use of tensor parameters as implemented in the Jana 2006 Software [101]. This method was already used to accurately describe complex structures that cannot be refined using conventional Pseudo-

Voigt pattern matching refinement [118]. For layered materials, the selective broadening of some peaks often highlights the presence of stacking faults [26,72,119] In agreement with the in situ XRPD experiment, the pattern of the almost fully intercalated phase is indexed in the monoclinic system (C2/m space group). Its cell parameters are very close to those found for the x = 0.96 composition in the in situ study. The Rietveld refinement of the Na content lead to x = 0.96 (2). The amon./bmon. ratio is equal to 1. -100-

A-II.2.a. Electrochemistry

Influence of the cut-off voltage

However, as this material showed electrochemical activity, more advanced characterizations were carried out to study the impact of the upper cut-off voltage. The galvanostatic E = f(x) curves recorded in As expected, the increase of the upper cut-off voltage leads to a better capacity for the first cycle.

For every experiment the first cycle is slightly different from the other ones which show a higher polarization and a smoother potential jump at x ≈ 0.55. While the 2 nd , 3 rd and 4 th cycles are similar for the Ecut-off = 3.8 V and 4.0 V curves. The Ecut-off = 4.3 V curve shows a decrease of the reversibly (de)intercalated sodium content between the 2 nd and 4 th cycles: from 0.68 Na + to 0.6 Na + per formula unit, respectively.

This phenomenon is correlated to the important discharge capacity loss observed for the first 6 cycles in

GITT cycling

To better understand the behavior of this material, a GITT experiment was carried out as shown in Figure A-II.18a. For comparison purposes, the GITT curve of the NaxMn1/3Fe2/3O2 material is given in

A-II.2.b. Operando in situ XRPD study during Na deintercalation

To follow the structural changes that the material undergoes during Na + deintercalation, we carried out an operando in situ XRPD study during the charge of a NaxMn1/2Fe1/2O2//Na battery. As for the experiment carried out on the O3-based NaxMn1/3Fe2/3O2 system, data were collected during the first charge following a preliminary discharge of the cell that lead to the Na0.95Mn1/2Fe1/2O2 composition as the starting point. In order to be close to the fully intercalated phase the galvanostatic discharge was followed NaxMn1/3Fe2/3O2 system, we believe that the observation of this new diffraction peak to be induced by the increasing amount of stacking faults into the P3-type material.

For x = 0.25 only one phase remains. This phase is labeled "X" by analogy to the experiment carried out in the O3-based NaxMn1/3Fe2/3O2 system. It exhibits a small interslab distance (≈ 5.3 Å) indicating an octahedral environment of the remaining Na + ions. Upon further deintercalation the interslab distance decreases, as observed for all O3-type AxMO2 (A = Li, Na) systems [116]. At the very end of the experiment the asymmetry on the low angle part of the (00l)"X" diffraction peak suggests the appearance of a new phase.

The O'3 → O3 → P3 → "X" structural evoluion upon charge is comparable to the structural behavior observed in the NaxMn1/3Fe2/3O2 system. Several residual diffraction peaks are observed during the experiment, as indicated by arrows in As one can see, the same monoclinic distortion is observed after the second discharge and the LeBail refinement of both patterns give the same cell parameters. We therefore conclude that cycling up to 4.3 V does not degrade the material after one cycle. In the NaxMn1/3Fe2/3O2 system, the same experiment did not lead to the monoclinic distortion of the structure of the intercalated phase. As both systems underwent the same structural transitions, it is possible that the higher Mn content in the NaxMn1/2Fe1/2O2 system stabilizes the material by preventing the Fe migration to the interlayer space. This could also explain the better capacity retention observed in the 1.5 -4.0 V range for Na0.77Mn1/2Fe1/2O2 (91 % after 30 cycles) compared to Na0.77Mn1/3Fe2/3O2 (74 % after 30 cycles). For reasons already mentioned, the profile of the diffraction peaks was fitted using anisotropic broadening of the diffraction peaks. The pattern of the intercalated O'3-NaxMn1/2Fe1/2O2 phase is indexed in monoclinic system (C2/m space group) with cell parameters very close to those determined in the in situ experiment. The refinement of the sodium content leads to the O'3-Na0.95Mn1/2Fe1/2O2 formula.

By comparison to the O'3-Na0.96Mn1/3Fe2/3O2 material, the higher Mn content of the O'3-Na0.95Mn1/2Fe1/2O2 material induces a more important cooperative Jahn Teller effect: (1) the amon./bmon. ratio is higher for the O'3-Na0.95Mn1/2Fe1/2O2 phase (1.84) than for the O'3-Na0.96Mn1/3Fe2/3O2 one (1.80) and ( 2) the distortion of the MO6 octahedra is higher as they exhibit longer (2 * 2.19(1) Å) and shorter (4 * 1.99(1) Å) M-O bonds than for the O'3-Na0.96Mn1/3Fe2/3O2 material (2 * 2.14(1) Å and 4 * 2.02(2) Å, respectively). The MO2 slab thickness is higher (2.18(1) Å) for O'3-Na0.96Mn1/3Fe2/3O2 than for O'3-Na0.95Mn1/2Fe1/2O2 (2.15(1) Å), which is coherent with the larger ionic radii of the Fe 3+ ion (r = 0.63 Å) compared to the Mn 3+ one (r = 0.58 Å).

The other structural domains (O3, P3) were not studied by synchrotron XRPD due to their similarity to the O3-NaxMn1/3Fe2/3O2 and P3-NaxMn1/3Fe2/3O2 ones and to time limitations. already give an insight of the activity ranges of the Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ redox couples as the voltage jumps are located at x ≈ 1/2 (which corresponds approximatively to the iron content in the NaxMn1/2Fe1/2O2 system) and at x ≈ 2/3 (which corresponds to the iron content in the NaxMn1/3Fe2/3O2 system). This suggests that the Mn 4+ /Mn 3+ redox couple is active at low voltage and that the Fe 4+ /Fe 3+ one is active at high voltage.

To confirm these assumptions, we carried out operando in situ X-ray absorption spectroscopy 11 and in situ and ex situ 57 Fe Mössbauer spectroscopy 12 measurements.

E (V)

A-II.3.a. Operando in situ X-ray Absorption Near Edge Spectroscopy study

The in situ X-ray Absorption Spectroscopy study was performed in operando due to the time limitations on the synchrotron beamline 13 . The evolution of the X-ray Absorption Near Edge Spectroscopy Concerning the NaxMn1/3Fe2/3O2 system, one can notice an important shift of the Mn K-edge towards the higher energy values as Na + is deintercalated from the structure in the 2/3 ≤ x < 1 range. We associate this shift to the Mn 3+ → Mn 4+ redox reaction as confirmed by the selected references (Figure A-II.26e). In the same sodium content region, no significant shift is observed on the Fe K-edge spectra, indicating that only the Mn 4+ /Mn 3+ redox couple is active at low potential / high sodium contents (x > 0.67) as suggested. For x < 0.67, no significant shift is observed on the spectra corresponding to the Mn K-edge while a small one is observed for the Fe K-edge. The references for the oxidation of Fe(III) consist in O3-NaFeO2 prepared by solid state chemistry and in a Na0.55FeO2 phase prepared by electrochemical deintercalation. Their XANES spectra are presented in Figure A-II.26f and only show a small shift in the spectrum position to higher energy values along with Na + deintercalation, which is similar to the behavior observed in our material. It is strongly suggested that the Fe 3+ → Fe 4+ redox process is associated to the higher voltages, confirming our assumption.

Concerning the NaxMn1/2Fe1/2O2 composition, a shift of the Mn K-edge is observed in the 0.5 < x < 1 and confirms the Mn 3+ → Mn 4+ redox reaction as discussed previously. The spectra of the Fe K-edge show no important variation from x = 0.91 to x = 0.62. Therefore, the Fe 4+ /Fe 3+ redox couple does not seem active in the high Na content (low voltage) region. For x < 0.62, the opposite tendencies are observed: the Mn K-edge spectra do not show any evolution between x = 0.51 and x = 0.46 while the Fe K-edge spectra show an important shift towards higher energies, especially in the 0.46 ≤ x ≤ 0.51 range, strongly suggesting the Fe 3+ → Fe 4+ redox process at high voltage. However, the XANES spectra cannot exclude the simultaneous oxidation of Mn 3+ and Fe 3+ on a very narrow x range as no spectra were recorded for 0.62 <

x < 0.51. Such a feature was already observed in our laboratory on the O3-LixNi0.30Co0.70O2 system by a 7 Li NMR study [START_REF] Carlier | In Lithium deintercalation in LiNi0.30Co0.70O2: Redox processes, electronic and ionic mobility as characterized by 7Li MAS NMR and electrical properties[END_REF] and could explain the smooth voltage jump observed at x ≈ 0.55 for the NaxMn1/2Fe1/2O2 system. Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe

A-II.3.b. 57 Fe Mössbauer spectroscopy study

To monitor the activity of the Fe 4+ /Fe 3+ redox couple during the electrochemical cycling, 57 Fe

Mössbauer spectroscopy was performed on both systems. As the NaxMn1/3Fe2/3O2 one exhibits the higher Fe content, its Mössbauer study was performed in situ and constituted a reference for other experiments.

Because of the important time that an in situ 57 Fe Mössbauer experiment requires (≈ 1 month) the study of the NaxMn1/2Fe1/2O2 system was performed ex situ.

In situ 57 -123-A preliminary refinement using Lorentzian profile lines gives the number of Fe n+ sites involved for each composition, as reported in Table A-II.8. For 0.67 ≤ x < 1, two Fe 3+ sites (δ ≈ 0.34 -0.37 mm.s -1 ) are required to describe the spectra. As they do not show an important shift upon deintercalation, one can conclude that the Fe 3+ ions are not involved in the redox process at low voltage and that only the Mn 3+ are oxidized upon Na + deintercalation. For x < 0.67, we note the appearance of the Fe 4+ (δ ≈ 0 mm.s -1 ) and Fe (3+z)+ (δ ≈ 0.10 -0.18 mm.s -1 ) sites, confirming that the Fe 3+ ions are oxidized at high voltage.

We observe an important broadening of the FWHM of the spectra upon deintercalation from x = 0.96 to x = 0.38. This observation is coherent with the appearance of new Fe n+ sites. It also suggests an increasing disorder in the material upon Na + deintercalation. To take into account this phenomenon a -124-

Awaited results from electrochemistry Mössbauer results

Developed formula %Fe 3+ %Fe 4+ for the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

-125-

The results can be separated in two groups, depending on the active redox process: Mn 3+ → Mn 4+ (x ≥ 2/3) and Fe 3+ → Fe 4+ (x < 2/3). The spectra corresponding to the x = 0.96, 0.85 and 0.67 samples are quite similar as shown in Figure A-II.28a and can be fitted using two Fe 3+ sites, as for the pristine material.

These sites are labelled as Fe 3+ (1) and Fe 3+ (2) to avoid any confusion with the sites deduced from the Lorentzian fit. The associated signals correspond to doublets which show very close isomer shifts (δ = 0.355 mm.s -1 and 0.365 mm.s -1 for the x = 0.96 composition). The quadrupole splitting Δ* values of the two Fe 3+ sites corresponding to the O'3 phase (x = 0.96) are quite different from each other (Δ* = 1.00 mm.s -1 and 0.71 mm.s -1 for the Fe 3+ (1) and Fe 3+ (2) sites respectively). As the Δ* parameter is directly correlated to the deformation of the FeO6 site, the high Δ* value for the Fe 3+ (1) site indicates that it is the most impacted by the cooperative Jahn-Teller effect of the surrounding Mn 3+ ions. Moreover, when the structure evolves from O'3 to O3, the Δ* value of the Fe 3+ (1) site decreases continuously indicating it is also the most impacted by the Mn 3+ → Mn 4+ redox reaction. In the meantime, the Δ* value of the Fe 3+ (2) site does not show any evolution. Therefore, we can conclude that the Fe 3+ (1) site corresponds to a local Fe environment mostly surrounded by Mn n+ ions (even though there is a distribution of environments) while the Fe 3+ (2) site corresponds to a local Fe environment mostly surrounded by other Fe 3+ ions (including also a distribution of environments). The populations of these two sites give an average Fe 3+ (1) : Fe 3+ (2) ratio of 40 : 60 and is maintained in the 0.96 ≥ x ≥ 0.67 range. In the same Na range, the isomeric shift (δ) values decreases, upon Na + deintercalation (from 0.355 mm.s -1 to 0.341 mm.s -1 for Fe 3+ (1) and from 0.365 mm.s -1 to 0.360 mm.s -1 for Fe 3+ (2)), in agreement with the increase of the Mn average oxidation state in the nearby Fe 3+ ion area.

For lower sodium contents (x < 0.67) all the Mn 3+ ions have been oxidized to Mn 4+ according to the XANES measurements and the active redox process is now Fe 3+ → Fe 4+ . The Mössbauer spectra of the x = 0.58 and x = 0.38 phases can be fitted using three Fe n+ sites. The first one shows an isomer shift of 0.336 -0.321 mm.s -1 (depending on the Na content) and is attributed to the HS-Fe 3+ ions in octahedral environments. The second one is characterized by an isomer shift close to 0 mm.s -1 , typical of the Fe 4+ ion in octahedral environment, as also observed in other oxides, in the High Spin [START_REF] Prado | [END_REF] or Low Spin [122,123] states. The spin state in our compounds has not yet been established. The existence of the Fe 3+ and Fe 4+ sites was predictable, based on the charge compensation in the material and was already investigated in the NaxFeO2 phase diagram by Takeda [35] and in the P2-NaxMn1/2Fe1/2O2 phase [26,28]. Confirming the developed formulae in state can be separated into the Fe 3+ and Fe 4+ ones considering that the sum of the populations of the involved Fe 3+ and Fe 4+ sites is equal to one and using the following formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )), where P(Fe 3+ ) is the population of the involved Fe 3+ ions. The repartition of the population of the Fe (3+z)+ site into the Fe 3+ and Fe 4+ ones is given in Table A-II.8. We observe good agreement between the material compositions deduced from the Mössbauer data (Na0.58Mn1/3Fe2/3O2 and Na0.40Mn1/3Fe2/3O2) and the ones deduced by electrochemistry (Na0.58Mn1/3Fe2/3O2 and Na0.38Mn1/3Fe2/3O2, respectively).

Furthermore, the Δ* values between the two samples increase significantly as Na + is removed from the system, and especially for the Fe 4+ site (Δ* = 0.19 mm.s -1 and 0.55 mm.s -1 for the x = 0.58 and x = 0.38 compositions respectively), indicating an increasing disorder inside the material from the x= 0.58 to the x = 0.38 compositions. This statement is in agreement with the in situ XRPD results which showed the coexistence of two phases: P3 (majority) and O3* (minority).

The Mössbauer results obtained on the NaxMn1/3Fe2/3O2 system show that the Mn 4+/3+ and Fe 4+/3+ redox couples are successively involved during the electrochemical deintercalation in agreement with the electrochemical results which show a sudden voltage increase for x = 2/3. 0.44 composition) or by a distribution one (x = 0.22). Independently of the fitting method three Mössbauer sites are required to successfully fit the spectra (Table A-II.9). The first one shows an isomer shift comprised between 0.336 and 0.35 mm.s -1 and corresponds to the remaining HS Fe 3+ ions. The second one

shows an isomer shift close to 0 mm.s -1 and is associated to Fe 4+ ions. The third site is characterized by an intermediate shift comprised between 0.321 mm.s -1 and 0.20 mm.s -1 as Na + is deintercalated. This site is associated to the fast electron hopping phenomenon (Fe 3+z site) between Fe 3+ and Fe 4+ , as discussed previously for the Fe rich system. The increasing Δ and Δ* values along with Na + deintercalation for the Fe (3+z)+ site (Δ = 0.72 mm.s -1 → Δ* = 0.94 mm.s -1 ) and Fe 4+ one (Δ = 0.1 mm.s -1 → Δ* = 0.64 mm.s -1 ) confirm the increasing disorder in the material upon Na + deintercalation, according to our operando in situ XRPD study.

The repartition of the population of the Fe (3+z)+ site between the Fe 3+ and Fe 4+ ones gives a Fe 3+ : The Mössbauer results obtained on the NaxMn1/2Fe1/2O2 system show that the Mn 4+/3+ and Fe 4+/3+ redox couples are successively involved during the electrochemical deintercalation, as in the NaxMn1/3Fe2/3O2 system. This conclusion is in agreement with the electrochemical results which show a smooth voltage increase for x ≈ 1/2.

-129- Velocity (mm.s -1 ) Absorption (%) Table A-II.9: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra of the NaxMn1/2Fe1/2O2 system presented in Figure A-II.29. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

In this chapter, the structural and electrochemical properties of the P2-based materials are investigated, first on the NaxMn1/2Fe1/2O2 system and then on the NaxMn2/3Fe1/3O2 one. The last part of this chapter focuses on the redox mechanisms involved upon Na deintercalation for both compositions.

A-III.1. The NaxMn1/2Fe1/2O2 system A-III.1.a. Synchrotron X-ray and neutron powder diffraction studies of the pristine material

Synchrotron X-ray Powder Diffraction

The synchrotron XRPD 14 The pattern is refined in the hexagonal P63/mmc space group, as expected for a P2 type phase.

The refined cell parameters (ahex. = 2.9405(1) Å and chex. = 11.1957(2) Å) are very close to those of the literature for the x = 0.67 composition [26]. The very good signal / noise ratio allows us to refine the occupation of the different Na sites along with the different isotropic ADPs. The overall sodium content is equal to 0.62 (3), which is in good agreement with the targeted composition (Na0.67Mn1/2Fe1/2O2) and the formula determined by ICP-AES analysis (Na0.66Mn0.47Fe0.53O2). In the following, this material is designed as P2-Na0.62Mn1/2Fe1/2O2. The associated ADPs are equal to 1.8(7) and 1.9(4) Ų for the two sodium sites (Naf and Nae) respectively. These high values are due to the high mobility of sodium in layered phases. The occupancies of the transition metal and oxygen sites were fixed to 1.0 and the associated ADP show more usual values of 0.29(3) Ų (Fe and Mn in 2a site) and 0.7(1) Ų (O in 4f site). We also tried to refine the transition metal site occupancy as previous work on P2-Na0.7MnO2 materials showed that some transition metal vacancies could occur [5,52,[START_REF] Stoyanova | [END_REF]. However, any attempt to include transition metal vacancies into the MO2 slabs did not lead to significant improvement of the refinement.

Neutron powder diffraction

Because of the 1:1 ratio between the Mn 3+/4+ and Fe 3+ ions, we considered the possibility of an ordering within the transition metal layer and the material was studied by neutron diffraction at ILL 15 .

The neutron powder diffraction pattern of the pristine material is shown in

(004) (002) (002) b)
-137-

A-III.1.b. Electrochemistry

Influence of the cut-off voltage

The -143-

However, the comparison between the different SEM micrographs presented in

GITT cycling

We then characterized the material in its relaxed state by carrying out a Galvanostatic Intermittent Titration Technique (GITT) experiment whose result is reported in different on both sides of the x = 0.5 composition which can be related to the electronic transfer between the involved cations. For x > 0.5 the Mn 3+ /Mn 4+ hopping is involved, while the Fe 3+ /Fe 4+ couple is only active for x < 0.50. The change in polarization is due to the easier electronic transfer in the case of the iron couple.

0 and Fe 3+ in the material which prevents from an easy electronic transfer.

Influence of the rate

As the P2-NaxMn1-yFeyO2 materials are more suitable for electrochemical applications than the O3 ones [26], the influence of the rate was studied for the P2-Na0.62Mn1/2Fe1/2O2 material. To carry this experiment, three cycles were successively realized at the following rates in the 1. As one can see, increasing the rate to C/10 or C/5 does not induce an important capacity loss, as 92 % and 82 % of the initial discharge capacity at C/20 are maintained, respectively. On the other hand, cycling at higher rate values induce an important decrease of the discharge capacity (50 %, 20 % and 8 % of the initial discharge capacity are still accessible when the rate is set to C/2, C and 2C). However, the cycling back to C/20 exhibits a discharge capacity close to the initial one (≈ 99 %), which indicates that the material is not damaged during the cycling carried out at higher rates and that the discharge capacity loss is only due to kinetic effects. The low discharge capacity reached at the 19 th cycle at C/20 is due to the low amount of Na + ions intercalated during the previous charge carried out at 2C.

A-III.1.c. Operando in situ study during Na deintercalation

To study the structural rearrangements occurring in the material upon cycling, we carried out an operando in situ XRPD experiment during the charge of a NaxMn1/2Fe1/2O2//Na battery. The experimental conditions were optimized in order to record XRPD patterns in the 13 -20° and 30 -43° 2θ ranges every 0.01 Na + per formula unit. The evolution of the XRPD patterns along with the complete charge of the battery is shown in Figures A-III.9 and A-III.10 in reverse order. -146-

The experiment starts from the material in the fully intercalated state which corresponds to the Na0.97Mn1/2Fe1/2O2 composition. On its diffraction pattern, two diffraction peaks -observed at approximately 37.4° and 38.8° -cannot be indexed using the hexagonal symmetry of the pristine material.

Instead, an orthorhombic cell should be used to index the pattern as for P'2-Na0.7MnO2 [START_REF] Stoyanova | [END_REF]. According to the structural classification of NaxMO2 phases, we will refer to this phase as P'2 type structure.

Therefore, these two diffraction peaks correspond respectively to the (022)P'2 and (112)P'2 reflections in the orthorhombic symmetry and arise from the splitting of the (102)P2 reflection in the hexagonal symmetry. The P'2 type structure is observed as a single phase only for a narrow Na-range: 0.95 < x ≤ 0.97. diagram at the end of charge is not possible as only two diffraction peaks are observed. However, we suspect that the MO2 layers glided upon sodium deintercalation imposes an octahedral environment for sodium ions as it was suggested by several authors in other P2-NaxMO2 materials [26,72]. Therefore, as we do not have any data about the packing type, we will refer to this deintercalated phase as "Z phase".

Two characteristic distances of layered oxide structures can be deduced from the indexation of the XRPD patterns recorded during the in situ experiment. The first one is the interslab distance which is the distance between two successive MO2 layers while the second one is the in-plane M-M distance. For both phases with P'2 and P2 type structures, the interslab distance is equal to half the c parameter. For the P2 type structure, there is only one in-plane M-M distance, equal to the ahex. parameter whereas for the P'2 type one, two different in-plane M-M distances can be found: one is equal to the aorth. parameter and one is equal to √(aorth. x in Na x Mn 1/2 Fe 1/2 O 2 "Z" P'2 phase P2 phase "Z" phase b orth. cell parameter (P'2) a orth. cell parameter (P'2) a hex. cell parameter (P2) M-M distance ("Z" phase) creation of stacking faults -148-Concerning the "Z" phase appearing at high voltage for which the XRPD patterns could not be indexed; only two diffraction lines are seen on the XRPD patterns. As they are very close to the (002)P2 and (100)P2 ones, one can assume that this material presents for the x = 0.25 composition an interslab distance of 5.3 Å and an in plane M-M distance equal to 2.88 Å. The absence of well-defined diffraction peaks shows that there is no long range ordering in the MO2 slab packing.

For a very general point of view, when the number of alkali ions in the interslab space is very small, the covalence of the bonds in the MO2 slab increases thanks to the transition metal oxidation. This leads to a decrease of the interslab thickness. In the case of P2 type phases this decrease will increases the repulsions between the oxygen layers of the NaO6 trigonal prism which is then strongly destabilized. To It is noteworthy that whereas two crystallographic sites can be occupied by the Na + ions in the P'2 orthorhombic structure in the Cmcm space group [START_REF] Stoyanova | [END_REF], only the one sharing edges with the surrounding MO6 octahedra is occupied here. Generally in P2 and P'2 types structure both Nae and Naf sites are simultaneously occupied with a ratio close to 2 : 1 [36,[START_REF] Stoyanova | [END_REF]. This distribution results from the strong Na + -Na + repulsion which is prevailing to the Na + -M 3+/4+ one. As adjacent Nae and Naf sites cannot be occupied simultaneously, the Na1Mn1/2Fe1/2O2 stoichiometry can only be reached if all Na + ions are located in one site. Therefore the most stable onei.e Nae (4c position) -is occupied as shown in

A-III.2. The NaxMn2/3Fe1/3O2 system

To emphasize the effect of the Mn / Fe ratio on the electrochemical and structural properties, several studies were carried out on the NaxMn2/3Fe1/3O2 system.

A-III.2.a. Synchrotron X-ray and neutron powder diffraction studies of the pristine material

Synchrotron X-ray Powder Diffraction

The synchrotron XRPD pattern 17 As for the P2-Na0.62Mn1/2Fe1/2O2 material, the pattern can be refined in the hexagonal P63/mmc space group using a Pseudo-Voigt function. The refined cell parameters (ahex. = 2.9400(1) Å and c hex. = 11.1812(2) Å) are close to the literature on P2-Na2/3Mn2/3Fe1/3O2: ahex. = 2.913 Å and c hex. = 11.262 Å [32].

The overall sodium content is equal to 0.66(4), which is lower than the expected one (x = 0.77) and the one from the formula determined by ICP-AES (Na0.77Mn0.64Fe0.36O2). This indicates that a more significant part of the Na + ions was expelled during the air quenching of the material than for the other studied materials. One can link the sodium loss to the high Mn 3+ content and its instability at low temperature: a more important part of the transition metal ions are susceptible to be oxidized to Mn 4+ , expelling more Na + ions at the surface of the material in the process. In the following we will refer to the material as P2-Na0.66Mn2/3Fe1/3O2. The global ADP value associated to the sodium sites is high (2.9(5) Å) and can be associated to a high disorder into the sodium layers. Any attempt to refine separately the ADP of the Na sites led to the divergence of the refinement. Occupancies of the transition metal and oxygen sites were fixed to 1.0 and the associated ADP's are equal to 0.65(4) Ų (Fe and Mn in 2a site) and 1.1(1) Ų (O in 4f site). By comparison to P2-Na0.62Mn1/2Fe1/2O2, we note higher ADP values, which imply a higher disorder in P2-Na0.66Mn2/3Fe1/3O2. This can be related to the higher amount of Jahn Teller active Mn 3+ ions in the pristine material which induce local distortions in the MO2 slabs, even if the structure is not distorted at the macroscopic scale. We also tried refining the transition metal site occupancy to verify the possibility of transition metal vacancies. However, any attempt to include transition metal vacancies into the MO2 slabs did not lead to significant improvement of the refinement.

-153-

Neutron Powder Diffraction

The 2:1 ratio between the Mn and Fe transition metal led us to consider the existence of a possible ordering within the MO2 slabs. To investigate this feature, we carried out neutron diffraction measurements at ILL 18 in order to differentiate the Mn and Fe species. The structure of the material was refined from the laboratory XRPD and neutron powder diffraction patterns as shown in 18 In collaboration with Dr. E. Suard, ILL, Grenoble, France.

(008) As for the other NaxMn1-yFeyO2 materials, we do not observe any extra diffraction peak on the neutron powder diffraction pattern. The existence of a long-range ordering between the Mn and Fe species is therefore excluded. The refined Mn and Fe contents are equal to 0.655(1) and 0.345 (1) respectively and are close to the targeted ones. There is an important difference between the overall sodium content deduced from the synchrotron XRPD (x = 0.66) and the one deduced from the combined refinement (x = 0.73). We explain this difference by the duration separating the various analyses: the synchrotron XRPD pattern was recorded six months after the neutron and laboratory XR diffraction patterns and the material probably reacted with moisture traces in the glovebox. This hypothesis is coherent with the increase of the chex. parameters deduced from the neutron diffraction pattern (chex. = 11.1588(3) Å) and from the synchrotron XRPD pattern (chex. = 11.1812(6) Å).

XRPD Neutron diffraction

Cell

A-III.2.b. Electrochemistry

Influence of the cut-off voltage

In order to have a better understanding of the performances and limitations of P2- During the first discharge a short voltage plateau is observed at ≈ 2.2 V and at ≈ 2.1 V upon following charge. Then the voltage continuously increases upon deintercalation. If the cut-off voltage is set to 3.8 or 4.0 V, the following discharge shows the reversibility of the Na (de)intercalation process.

When the cut-off voltage in increased to 4.3 V a second voltage plateau is observed at ≈ 4.15 V. This plateau is not visible on the consecutive discharge curve and instead an increase of the polarization is observed. -157-Then the (de)intercalation process is reversible for E < 3.2 V. For every experiment, the 2 nd , 3 rd and 4 th cycles are very similar. Our observations are in agreement with the literature on the same system when cycled in the 1.5 -3.8 V [66] and 1.5 -4.3 V ranges [32].

The evolution of the discharge capacities was also studied as shown in

GITT cycling

In order to have an insight of the phenomenon occurring during the cycling, a GITT experiment was performed, as shown in We do not have any explanation for this phenomenon that is also observed in galvanostatic cycling and only during the first cycle.

Furthermore, one can be surprised that no significant voltage jump is observed at x = 1/3 contrarily to the NaxMn1/2Fe1/2O2 system where a strong voltage jump is observed for x = 1/2. Instead, a small increase of the polarization of the cell is observed at E = 3.4 V (x ≈ 0.37). In the P2-based NaxMn1/2Fe1/2O2 system, the same increase of the polarization occurs at the voltage jump, also at E = 3.4 V (Figure A-III.18b).

One can see the signature of the change of redox process, from Mn 3+ → Mn 4+ to Fe 3+ → Fe 4+ . redox process, the M 4+ -O bonds being more covalent than the M 3+ -O ones. For x < 0.20, we observe a continuous decrease of the intensity of the diffraction lines of the P2 phase. Simultaneously, a broadening of the (002)P2 diffraction peak is observed on the high angle side and a new diffraction peak appears in the 16.7 ≤ 2θ ≤ 16.9 ° region. This behavior is very similar to the one observed in the other P2 and O3-based systems at the end of charge. As for the P2-based NaxMn1/2Fe1/2O2 system, we assume that stacking faults consisting in layers of NaO6 octahedrons are created among the P2 layers in the material for x < 0.20.

Contrarily to the other systems, we do not reach the deintercalation state where the diffraction lines merge to create the pure "Z" (P2-based systems) or "X" (O3-based systems) phases. As one can see, the two XRPD patterns exhibit well-defined diffraction peaks, which indicate that the cycling up to 4.3 V does not damage the material after one cycle. Both patterns are indexed in the Cmcm space group (P'2 phase) and show very close cell parameters. No noticeable broadening of the diffraction peaks is observed between the two patterns.

GITT in situ study during the Na intercalation from P2-Na0.66Mn2/3Fe1/3O2

This experiment carried out during a GITT discharge aimed to confirm the behavior we observed x in Na x Mn 2/3 Fe x in Na x Mn 2/3 Fe and Mn 4+ /Mn 3+ are well separated.

x in Na x Mn The operando in situ X-ray absorption spectroscopy study was performed on the NaxMn1/2Fe1/2O2 system 19 , starting from the intercalated state of the material. The evolution of the X-ray absorption near edge spectroscopy parts of the spectrum are shown in Unfortunately, we do not have X-ray absorption spectroscopy data for the NaxMn2/3Fe1/3O2 system yet. associates this shift to the Mn 3+ → Mn 4+ redox process. In the same range, a small continuous shift is observed on the Fe K-edge spectra. As the same phenomenon was observed for the O3-NaxMn1/2Fe1/2O2 -172-system (Chapter A-II), one can suppose that the higher Mn content of these materials leads to the oxidation of isolated Fe 3+ cations surrounded by more Mn 4+ cations.

For x ≤ 0.47, no significant shift is observed for the spectra of the Mn K-edge. On the other hand a more important shift towards the higher energy region is observed for the Fe K-edge spectra. The comparison to the Fe references (Figure A-III.29d) strongly suggests that the Fe 3+ → Fe 4+ redox process is involved in the high voltage region.

A-III.3.b. Ex situ 57 Fe Mössbauer study

Ex situ 57 Fe Mössbauer study of the P2-based NaxMn1/2Fe1/2O2 system

To confirm the Fe 3+ → Fe 4+ redox process and to study the structure of the materials using the Fe atoms as a local probe, we carried out 57 Fe Mössbauer spectroscopy measurements. The spectrum of the P2-Na0.62Mn1/2Fe1/2O2 pristine material was recorded and is shown in ). This implies that the presence of 12% of Mn 3+ O6 octahedra is enough to impact the FeO6 ones (distribution of the surroundings). Velocity (mm.s -1 ) Absorption (%) e) "Z"-Na 0.24 Mn 1/2 Fe increase continuously from x = 0.62 to x = 0.14. The Mössbauer spectra can be separated into two groups depending on the redox process: Mn 3+ → Mn 4+ (x ≥ 0.5) or Fe 3+ → Fe 4+ (x < 0.5).

The spectrum of the intercalated material ( The existence of the three Mössbauer sites in the x ≈ 1 and x = 0.50 samples suggests that three sites are also present in the pristine material. However, they are too close to be separated in a Lorentzian or distribution fit.

For x < 0.5, we expect all the Mn 3+ ions to be oxidized to Mn 4+ ions. The spectrum of the P2-Na0.45Mn1/2Fe1/2O2 material can be fitted by four quadrupole doublets in a Lorentzian fit: two Fe 3+ sites, a Fe (3+z)+ site and a Fe 4+ one. Once again the two Fe 3+ sites show very close isomer shift values (δFe3+(A) = 0.333 mm.s -1 and δFe3+(B) = 0.335 mm.s -1 ) whose corresponding quadrupole splitting implies a highly distorted Fe 3+ site (ΔFe3+(A) = 0.93 mm.s -1 ) and a less distorted one (ΔFe3+(B) = 0.76 mm.s -1 ). The associated FWHM values show the same tendency as the first one is broader (ΓFe3+(A) = 0.31 mm.s -1 ) than the second (ΓFe3+(B) = 0.23 mm.s -1 ). As expected, we note the apparition of a Fe 4+ quadrupole doublet at δFe4+ = 0.00 mm.s -1 , confirming the Fe 3+ → Fe 4+ redox process. However, we cannot conclude on the spin state of the Fe 4+ ions.

As for the 57 Fe Mössbauer study of the O3-based materials, a Fe (3+z)+ site is also needed to describe the spectrum. It is characterized intermediate values of the isomer shift (δFe(3+z)+ = 0.319 mm.s -1 ), quadrupole splitting (ΔFe(3+z)+ = 0.60 mm.s -1 ) and FWHM (ΓFe(3+z)+ = 0.38 mm.s -1 ). Mössbauer spectroscopy gives the -178-following formula for the material: Na0.48Mn1/2Fe1/2O2. We note a small gap to the formula expected from electrochemistry (Na0.45Mn1/2Fe1/2O2).

The next two spectra correspond to the "Z" phase and show a broad quadrupole doublet which can only be described using a distribution fitting involving three Fe sites: Fe 3+ , Fe 4+ and Fe (3+z)+ . The FWHM have been fixed to reasonable values for the fit (0.25 mm.s -1 ) and so were the isomeric shifts (δFe3+ = 0.35 mm.s -1 , δFe(3+z)+ = 0.17 mm.s -1 and δFe4+ = -0.05 mm.s -1 ). The fit of the spectra give increasing quadrupole splitting values (from 0.85 to 0.90 mm.s -1 for ΔFe3+ and from 0.86 to 0.90 mm.s -1 for ΔFe(3+z)+) highlighting an increasing disorder in the material, in agreement with the operando in situ XRPD results.

The determined formulae are Na0.41Mn1/2Fe1/2O2 and Na0.36Mn1/2Fe1/2O2 while the expected ones from electrochemistry Na0.24Mn1/2Fe1/2O2 and Na0.14Mn1/2Fe1/2O2, respectively. These sodium contents are again significantly lower than the expected ones. As for the O3-based NaxMn1/2Fe1/2O2 system, underestimation of the Na content, which lead to an overestimation of the Fe 4+ one, would explain the differences between the expected formulae and the ones deduced from Mössbauer spectroscopy.

Furthermore, the most deintercalated samples (x = 0.24 and x = 0. The Mössbauer results obtained on the P2-based NaxMn1/2Fe1/2O2 system are very similar to the ones of the O3-based NaxMn1/2Fe1/2O2 system. They show that the Mn 4+/3+ and Fe 4+/3+ redox couples are successively involved during the electrochemical deintercalation, in agreement with the X-ray absorption spectroscopy study.

Ex situ 57 Fe Mössbauer study of the P2-based NaxMn2/3Fe1/3O2 system

The NaxMn2/3Fe1/3O2 system was also investigated by 57 The spectrum of P'2-Na0.96Mn2/3Fe1/3O2 exhibits a quadrupole doublet that a preliminary

Lorentzian fit attributes to HS Fe 3+ ions (δFe3+ = 0.351 mm.s -1 ). The distribution fit reveals high FWHM and quadrupole splitting values (Γ = 0.30 mm.s -1 and Δ* = 1.31 mm.s -1 ) thus indicating an important distortion of the FeO6 octahedra, due to the high cooperative Jahn-Teller effect of the Mn 3+ ions (64 % of the transition metal ions).

The spectrum of the deintercalated material: Na0.26Mn2/3Fe1/3O2 exhibits a broad quadrupole doublet resulting from the contribution of Fe 3+ (δFe3+ = 0.35 mm.s -1 ) and Fe 4+ (δFe4+ = -0.05 mm.s -1 ) ions.

Electron hopping is involved between a fraction of these two ions as an third isomeric shift with intermediate value is required to fit the spectrum (δFe(3+z)+ = 0.17 mm.s -1 ). The high quadrupole splitting values (Δ*Fe3+ = 0.79 mm.s -1 , Δ*Fe4+ = 0.47 mm.s -1 and Δ*Fe(3+z)+ = 0.92 mm.s -1 ) imply high disorder within the material, in agreement with in situ XRPD results (both P2 and "Z" phases are expected in this material).

The formula deduced from the Mössbauer data is similar to the expected one from electrochemistry (Na0.25Mn2/3Fe1/3O2 vs. Na0.26Mn2/3Fe1/3O2).

The Mössbauer results obtained on the P2-based NaxMn2/3Fe1/3O2 system show that the Mn 4+/3+

and Fe 4+/3+ redox couples are successively involved during the electrochemical deintercalation, as for the other NaxMn1-yFeyO2 systems. This conclusion is in agreement with the small increase of the polarization observed for x ≈ 1/3 on the GITT cycling curve (Figure A-III.18a). The influence of the rate on the discharge capacities of the P2 materials was also studied (Chapter As previously discussed, we observe an important decrease of the discharge capacity when the rate is higher than C/5 for both materials. However, comparing the two materials, the NaxMn2/3Fe1/3O2 system appears more suitable to handle high C-rate cycling than the NaxMn1/2Fe1/2O2 one: 28 % and 16 % of the capacity at C/20 are still accessible at C and 2C rates vs. 20 % and 8 % for the NaxMn1/2Fe1/2O2 system. Based on this observation, the NaxMn2/3Fe1/3O2 system seems more suitable to handle the important rate variations and thus to constitute the positive electrode active material of hypothetical Na-ion cells. Furthermore, we can consider increasing the discharge capacity and the power density by cycling the NaxMn2/3Fe1/3O2 system up to 4.1 V (before reaching the high voltage plateau). % of initial discharge capacity (%)

A-III) and is reminded in

A-IV.2. Effect of the Mn content on the structural properties A-IV-2.a. Impact on the phase diagrams

The shape of the galvanostatic curves discussed in Concerning the O3-type materials, we observe that increasing the Mn / Fe ratio from 1 / 2 to 1 / 1 leads to the observation of the O'3-type phase on a wider x range, in agreement with the higher Mn 3+ content expected. Increasing the Mn content also leads to the apparition of the P3-type phase for higher

x values (x = 0.7 for the NaxMn1/2Fe1/2O2 system vs. x = 0.62 for the NaxMn1/3Fe2/3O2 system). The P3-type phase is also observed in a wider range in the O3-based NaxMn1/2Fe1/2O2 system (0.39 ≤ x ≤ 0.7 vs. 0.39 ≤

x ≤ 0.62 in the NaxMn1/3Fe2/3O2 system). For both O3-based systems, stacking faults are created for x < 0.39 and lead to the "X" phase.

-193-

A-IV-2.b. Impact on the intercalated state and on the cooperative Jahn-Teller effect

As discussed along with Figure A-IV.6, increasing the Mn content leads to the observation of the distorted phase on wider range, because of the cooperative Jahn-Teller effect induced by the Mn 3+ ions.

To study the evolution of the cooperative Jahn-Teller effect with the Mn / Fe ratio, we first study the evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-yFeyO2 materials.

This evolution is shown in Figure A-IV.8. In order to make the interpretation easier, we considered all the Mn n+ ions to be in the +III oxidation state. The data for the O3-NaFeO2 and O'3-NaMnO2 phase have been added from the literature [35,44] for comparison purposes. As one can see, the evolution of the amon./bmon. or borth./aorth. ratios is linear for our experimental results (NaxMn1-yFeyO2 with y = 1/3, 1/2 and 2/3) with the increase of the Mn content. 1.99 Å and 2 x 2.18 Å (P'2 material). We also observe that the MO6 octahedra are more distorted when the Mn 3+ content increase as the M-O distances are equal to 4 x 2.02 Å and 2 x 2.14 Å (O'3-Na≈1Mn1/3Fe2/3O2) and to 4 x 1.94 Å and 2 x 2.39 Å (O'3-NaMnO2), in agreement with the higher quantity of Mn 3+ ions. reflection. Its origin will be explained later.

As one can see, every sample exhibits well defined diffraction peaks but show different widths at half maximum. In XRPD, the broadening of the diffraction peaks is strongly correlated to the decrease of the coherent lengths. This observation suggests that our materials have different particle sizes.

The cell parameters of the different samples were determined by LeBail refinement of the profiles and are given in -205-During the first discharge, no significant amount of Na + ions is inserted in the materials exhibiting large or medium grains. On the other hand, we observe that ≈ 0.01 Na + ions are inserted in the "small grains" sample. In the consecutive charge, the electrochemical profile exhibits several potential plateaus within the borders of peculiar compositions for x = 1, 2/3, 1/2 and 2/5. A solid solution behavior is then observed in the 1/3 < x < 2/5 range. The peculiar compositions observed at x = 2/3, 1/2, 2/5 and 1/3 correspond to the ones observed at x' = 0.91, 0.84, 0.81 and 0.79 in [38], respectively. They are highlighted in the dE/dx curve (Figure B-I.5e). The difference between the sodium intercalation amounts could come from the more reliable characterization techniques we used for our study. Depending on the particle size, the voltage plateau observed in the 2/3 < x < 1 range is slightly different and can be divided in one (large grains) or two (medium and small grains) parts. This point will be further discussed along with the GITT cycling curves. As discussed later, the O'3 / P'3 stacking types determined by the authors of [38] for x = 2/3, 1/2, 2/5 and 1/3 (highlighted in red in Figure B-I.5) were confirmed by synchrotron XRPD and XRPD measurements. The phases were labelled (P'3, P''3…) accordingly to [38].

(-203) (003) (111)
Upon the second discharge, we notice the partial reversibility of the (de)intercalation process. The curves exhibit two differences with the first charge ones: (i) the voltage jump observed at x ≈ 2/5 in charge is characterized by two smaller jumps in discharge and (ii) the maximal intercalated content in the second discharge curves is reached at x ≈ 0.83 (large and medium grains) or x ≈ 0.87 (small grains) instead of x ≈ 1. This phenomenon was already observed by Vassilliaras et al. [34]. The following charge shows the apparition of a solid solution domain whose range varies depending on the particle size: 0.80 < x ≤ 0.83 (large grains), 0.78 ≤ x ≤ 0.83 (medium grains) or 0.79 < x ≤ 0.88 (small grains). Then the first and second charge curves show the same profile for x > 2/3. After 50 cycles, all materials exhibit poor discharge capacity retention of ≈ 70 %, in agreement with literature [34].

B-I.4.b. GITT cyclings

To have a better understanding of the electrochemical behavior of O'3-NaNiO2 upon Na + deintercalation, we carried out a GITT measurement during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na battery as reported in Figure B-I.6. The sodium deintercalation step was 0.005 Na + /formula unit (C-rate: C/50) and the relaxation time was fixed to 30 minutes. The "medium grains" sample was selected as it represents the best compromise between the particle size (see SEM micrographs in The GITT cycling curve corresponding to the charge of the battery shows an altering between peculiar compositions and biphasic domains, as previously stated. In the 2/3 ≤ x ≤ 1.0 range, two voltage pseudo-plateaus are observed. This phenomenon will be detailed later for the three materials. In the 1/2 ≤ x ≤ 2/3 range, we note the appearance of an intermediate plateau in the GITT cycling curve, indicating a new phenomenon at x ≈ 0.55, that is hardly evidenced on the galvanostatic curve. This feature is highlighted on the insert of Figure B-I.6. One more plateau is finally observed between the x = 1/2 and x = 2/5 compositions while further deintercalation leads to a solid solution behavior down to x = 1/3. For E > 3.9 V (x > 1/3), no more variation on the voltage is observed and only a long plateau -cut for representation purposes-is visible. One can suppose the origin of this plateau to be the decomposition of the electrolyte in the battery. Nonetheless, one can observe an increase of the voltage at x ≈ 0, indicating the beginning of a new reaction.

Concerning the evolution of the polarization of the battery, we note the higher polarization for x > 0.8 (250 mV ≤ ΔE ≤ 500 mV). The 2/3 ≥ x ≥ 2/5 region of the curve exhibits a very low polarization (ΔE ≈ 10 mV). In the literature, Braconnier et al. highlighted the existence of P'3 structure types for the x = 2/3 and x = 1/2 compositions [38]. The decrease of the polarization is in agreement with this result as a higher ionic conductivity is expected from the P'3 phases [START_REF] Didier | Etude des oxydes lamellaires NaxVO2 : électrochimie, structure et propriétés physiques[END_REF]. For x < 2/5 the polarization increases to ΔE ≈ 30 mV, in agreement with the O'3 type structure observed by Braconnier et al. [38].

x in Na x NiO 2 b) Medium grains 0.5 0.6 0.7 0.8 0.9 1.0

E (V)

x in Na x NiO 2 c) Small grains -208-In the 2/3 ≤ x ≤ 1 range, the "large grains" sample shows only one voltage plateau associated to a high polarization (ΔE ≈ 90 mV) whereas the "medium grains" and "small grains" materials exhibit two distinct voltage plateaus separated by a small solid solution domain for 0.82 < x < 0.88 ("medium grains" curve values). As expected the polarization varies in the same way for the three materials. It decreases from the "large grains" sample to the "medium grains" one. Surprisingly, decreasing the grains size leads to an increase of the polarization. One can suppose this polarization increase to result from the grain boundaries resistances, more numerous in the case of the "small grains" sample. The voltage variation during Na + diffusion (end of relaxation step) is comparable to the one of the "medium grains" material.

B-I.5. The NaxNiO2 phase diagram B-I.5.a. In situ XRPD during full charge of the battery

To follow the structural changes that NaxNiO2 undergoes during Na + deintercalation, we carried out an in situ XRPD study during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2wt% FEC/Na battery on the "medium grains" sample. Due to the expected Na/vacancy orderings for precise Na contents, we carried out the experiment in the GITT mode to obtain each XRPD pattern at the equilibrium with a satisfying signal/noise ratio. The XRPD patterns were recorded between 15° and 45° (2θ) using the monochromatic In the 2/3 < x < 0.8 range a biphasic behavior is observed between the P'3-Na2/3NiO2 phase and the Na≈0.8NiO2 one. While the interslab distance of the P'3-Na2/3NiO2 phase does not evolve, we note a small evolution of the interslab distance of the Na≈0.8NiO2 phase which is, once more, involved in a solid solution behavior inside the biphasic domain.

In the 1/2 < x < 2/3 range, two biphasic domains are observed. For the higher sodium contents (XRPD patterns #13 → 15), a biphasic behavior is observed between P'3-Na 2/3NiO2 and P''3-Na0.55NiO2. The P''3-Na0.55NiO2 phase corresponds to the small voltage increase observed on the GITT cycling curve and evidenced by the red arrow in For lower sodium contents (XRPD patterns #16 → 18) the P''3-Na1/2NiO2 phase appears while the intensity of the diffraction peaks of the P''3-Na0.55NiO2 and P'3-Na2/3NiO2 phases decrease. The presence of the P'3-Na2/3NiO2 phase in the 1/2 < x < 0.55 implies slow kinetics for the P'3-Na2/3NiO2 phase. Upon deintercalation, one would expect the interslab distance of the material to continuously increase for a given phase. However, its value is very similar between P''3-Na1/2NiO2 (≈ 5.58 Å) and O''3-Na2/5NiO2 (≈ 5.59 Å) which is explained by the evolution of the NaO6 surrounding from a prismatic site to a more compact octahedral one. Between the two compositions a complex behavior is observed: first the interslab distance increases between pattern #18 (x = 1/2) and pattern #20. The interslab is then constant from patterns #20 to #21. It then decreases from pattern #21 to #22. In fact two opposite effects are in competition from pattern #18 to #22:

(1) The deintercalation from P''3-Na1/2NiO2 which implies an increase of the interslab distance.

(2) The formation of an octahedral environment for some NaO6 polyhedra slabs which leads to a decrease of the interslab distance. As one can see, the XRPD patterns of the x = 2/3, 1/2, 2/5 and 1/3 compositions all exhibit extra diffraction peak(s). In NaxMO2 oxides, such a phenomenon is commonly observed for peculiar compositions and is the consequence of long-range Na/vacancies ordering between the MO2 layers [48,56,64]. Including the extra-diffraction peaks in the LeBail refinement of the profile require determining new cell parameters for the supercell, based on the ones of the subcell. Note that the supercell and subcell do not always share the same space group. The behavior of the "large grains" sample shows that there are large kinetic differences between the O'3-NaNiO2, Na≈0.8NiO2 and P'3-Na2/3NiO2 phases. As soon as the Na≈0.8NiO2 phase is formed, it transforms rapidly into P'3-Na2/3NiO2. Due to the very small voltage difference between the pseudoplateaus, and the high polarization in the case of the "large grains" sample, the cell voltage is always above the Na≈0.8NiO2 → P'3-Na2/3NiO2 redox potential. In the case of the "medium grains" and "small grains" samples, there is a small polarization and, therefore, the O'3-NaNiO2 → Na≈0.8NiO2 and Na≈0.8NiO2 → P'3-Na2/3NiO2 phenomenons are separated.

B-I.5.c. Investigation of the deintercalated phases

The P'3-Na2/3NiO2, P''3-Na1/2NiO2 and O''3-Na2/5NiO2 phases

To further study the structure of the NaxNiO2 materials we recorded their synchrotron XRPD patterns at the ESRF 20 As the only differences between the two structures are the O and Na atomic positions, it is easy to discriminate the P'3 structure from the O'3 one based on the relative intensities of selected diffraction peaks. Typically, the XRPD patterns of P'3 structures exhibit (111) The better signal / noise ratio of the synchrotron XRPD patterns allows better distinction of the superstructure peaks. Therefore, we tried to find the superstructure cells of P'3-Na2/3NiO2, P''3-Na1/2NiO2 and O''3-Na2/5NiO2 from the synchrotron XRPD patterns. The first step was to index the subcell in the monoclinic symmetry (space group C2/m) independently of the stacking type (P'3 or O'3). The cell parameters determined for P'3-Na2/3NiO2, P''3-Na1/2NiO2 and O''3-Na2/5NiO2 are reported in Table B-I.4. 20 In collaboration with Dr. C. Drathen, ESRF, Grenoble, France (ID31 beamline).

-218-Then we tried fitting the synchrotron XRPD patterns with various supercells whose cell parameters were based on the subcell ones. The centrosymmetric space group of lowest symmetry (P-1) was considered for this step. After we determined the only possible supercell parameters, we deduced the space group (monoclinic symmetry) based on the reflection conditions. For every material, we found only the broadening of the diffraction peaks. An indexation based on the monoclinic cell parameters as described in [134] was not successful either.

Introduction générale

La maitrise de l'énergie et de sa production furent les étapes nécessaires à l'établissement de la société moderne. est nettement supérieure à celle observée dans la littérature, typiquement de l'ordre de 500 nm [26]. Cela est certainement dû à la température de synthèse plus élevée de nos matériaux (1000 °C vs. 700 °C [26,[START_REF] Yabuuchi | th ECS Meeting Abstract #[END_REF]). -234-Lors de la charge consécutive le même plateau en potentiel est observé, indiquant la bonne réversibilité du processus. Le potentiel augmente ensuite de façon continu et décrit un saut en potentiel pour x ≈ yFe pour les matériaux pour lesquels le rapport Mn / Fe est égal à 1 / 1 ou 1 /2. Ces sauts correspondent au changement de processus redox (de Mn 3+ → Mn 4+ à Fe 3+ → Fe 4+ ) comme cela a été montré dans la littérature par spectroscopie d'absorption des rayons-X et spectroscopie Mössbauer [26,28]. Si pour les systèmes de type P2 la première décharge est similaire aux suivantes, nous pouvons observer une augmentation de la polarisation en fonction du nombre de cycles pour les systèmes de type O3.

Electrochimie

L'évolution de la capacité en décharge a été extraite pour chaque courbe et est reportée La comparaison des capacités en décharge aux seconds cycles montre un maximum pour la phase P2-Na0.66Mn2/3Fe1/3O2 (144 mAh.g -1 ). La diminution du rapport Mn / Fe pour les systèmes de type P2 entraine une diminution de la capacité (133 mAh.g -1 ). Le phénomène contraire est observé pour les systèmes de type O3 et diminuer le rapport Mn / Fe entraine une augmentation de la capacité en décharge au second cycle (de 124 mAh.g -1 pour NaxMn1/2Fe1/2O2 à 133 mAh.g -1 pour NaxMn1/3Fe2/3O2). La comparaison des systèmes P2 et O3 montre que les capacités en décharges sont plus élevées pour les phases de type P2, en accord avec la littérature [26]. x in Na

x Mn Concernant les systèmes de type O3, l'augmentation du rapport Mn : Fe de 1 : 2 à 1 : 1 entraine (i) un domaine d'observation de la phase O'3 plus étendu et (ii) une apparition plus rapide de la phase P3

(pour x = 0.

R.2.c. Electrochimie

Le comportement électrochimique de O'3-NaNiO2 « moyens grains » a été étudié en batteries Na Au cours de la mesure GITT, on remarque une diminution continue de la polarisation pour 2/5 ≤ x ≤ 1. Cette observation est cohérente avec le changement de structure attendu (O'3 → P'3) [38], les matériaux de type P3 / P'3 se montrant de meilleures conducteurs ioniques [START_REF] Didier | Etude des oxydes lamellaires NaxVO2 : électrochimie, structure et propriétés physiques[END_REF]. L'augmentation de la polarisation observée pour x ≤ 2/5 résulte de la transition structurale P'3 → O'3 [38].

R.2.d. Le diagramme de phase de NaxNiO2

Le diagramme de phase de NaxNiO2 (1) La désintercalation à partir de P''3-Na1/2NiO2 qui entraine une augmentation de la distance inter-feuillets.

(2) La formation d'un environnement octaédrique pour certains feuillets NaO6 qui entraine une diminution de la distance inter-feuillets.

-263-

Conclusion générale

Ces travaux représentent une étude des propriétés structurales et électrochimiques des systèmes NaxMn1-yFeyO2 et NaxNiO2 utilisés en tant qu'électrodes positives en batteries Na-ion.

La première partie de ce manuscrit concerne la préparation par synthèse de type auto-combustion de quatre phases du système NaxMn1-yFeyO2 : P2-Na0.66Mn2/3Fe1/3O2, P2-Na0.62Mn1/2Fe1/2O2, (O3 + O'3)-Na0.77Mn1/2Fe1/2O2 et O3-Na0.77Mn1/3Fe2/3O2. Nous avons montré qu'un rapport Mn : Fe élevé stabilisait l'empilement de type P2 tandis qu'un rapport Mn : Fe faible stabilisait l'empilement de type O3.

Parallèlement à ces travaux de thèse, plusieurs études traitant des phases P2 Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

-270- The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )). (phases P'2) en fonction du rapport Mn : Fe. O3-NaFeO2 : données provenant de [35]. O'3-NaMnO2 : données provenant de [44]. O'3-NaMnO2 : données provenant de [44].

-277-

  8NiO2 est observée et empêche le retour à O'3-NaNiO2 Mots clés : Batteries Na, matériaux d'électrode positive, oxydes lamellaires de sodium, mécanismes d'intercalation / désintercalation électrochimiques. Institut de Chimie de la Matière Condensée de Bordeaux ICMCB/CNRS -UPR 9048 87, avenue du Docteur Schweitzer, 33608 Pessac Cedex -8-First, I would like to express my sincere gratitude to my supervisors: Dany CARLIER, Marie GUIGNARD and Claude DELMAS. They showed me great confidence and were of fantastic counselling during these three years. Their warm welcome made of the ICMCB a second home. I would also like to thank Mario MAGLIONE for welcoming me at the ICMCB which was a highly stimulating environment to work in. I am deeply thankful to the members of the jury: Florent BOUCHER and Christian MASQUELIER as rapporteurs, Bing-Joe HWANG as reviewer and Mario MAGLIONE as President. This work would not have been possible without the financial support from the following institutions: Région Aquitaine, Centre National de la Recherche Scientifique and Agence Nationale pour la Recherche (Blanc Inter II, SIMI 8) n° 2011-IS08-01. I would like to express my sincere thanks to everyone who contributed on this work at the ICMCB: Laurence CROGUENNEC (supervisor of Groupe 2 : Matériaux et batteries, for her advices and her help), Mélissa ARNAULT (experimental help), Sylvie BORDERE (Mössbauer spectroscopy), Philippe DAGAULT (TGA / DSC), Jacques DARRIET (XRD data interpretation), Cathy DENAGE (from experimental help to day-to-day in the laboratory help), Dominique DENUX (TGA / DSC), Graziella GOGLIO (auto-combustion type synthesis related discussions), Eric LEBRAUD (XRD experimental setups), Olivier NGUYEN (SQUID measurements), Stanislav PECHEV (XRD experimental setups), Sandrine QUILLATEAU (welcome desk), Stéphane TOULIN (Library) and François WEILL (TEM). I distinctively wish to acknowledge and thank Alain WATTIAUX for introducing me to Mössbauer spectroscopy through our experiments, the GFSM congresses and numerous discussions. A significant part of this work was carried out outside the ICMCB and I express my sincere gratitude to the following persons: Lydie BOURGEOIS (ISM, Raman spectroscopy), Christina DRATHEN (ESRF, synchrotron diffraction), Dmitry FILIMONOV (Lomonosov Moscow University, Mössbauer in situ cell design and discussion), Bing-Joe HWANG and his research team (NTUST / NSRRC, X-ray absorption spectroscopy experiments), Emmanuelle SUARD (ILL, neutron diffraction), Radostina STOYANOVA (Bulgarian Academy of Science, EPR experiments), Matthew SUCHOMEL (APS, synchrotron diffraction) and Thanya PHRAEWPHIPHAT (experiments on the NaNiO2 system, Tokyo Institute of Technology).

I. 1 .

 1 Structure of the NaxMO2 layered oxides ................................................................................... I.1.a. The α-NaFeO2 structure ......................................................................................................... I.1.b. Other NaxMO2 structures ....................................................................................................... I.1.c. Distorted structures and the cooperative Jahn-Teller Effect ................................................... I.1.d. Determination of the distances in the hexagonal and distorted structures ............................ I.2. NaxMO2 layered oxides as positive electrode materials in Na and Na-ion batteries ................... I.2.a. Principle of Na and Na-ion batteries ...................................................................................... I.2.b. Electrochemical variables ...................................................................................................... I.2.c. The galvanostatic curves ........................................................................................................ I.2.d. NaxMO2 layered oxides in the literature ................................................................................. -22-

I. 1 .

 1 Structure of the NaxMO2 layered oxides I.1.a. The α-NaFeO2 structure

Figure I. 1 ,

 1 which leads to the rhombohedral distortion of the cubic cell (Figure I.1b).

Figure I. 1 :

 1 Figure I.1: Representations of (a) the α-NaFeO2 structure in the NaCl rock salt-type structure and (b) the distortion of the cell due to the Na + / Fe 3+ altering. Cell and atomic parameters from [35].

  and LS d 7 electronic configurations we encountered during this work are represented in Figure I.4 and clearly show the lowering of the energy accompanying the lift of degeneracy. The ML6 octahedra are represented with oxygen atoms as ligands.

Figure I. 4 :

 4 Figure I.4: Representation of the ground electronic states and lift of degeneracy of 3d orbitals for the (a) HS 3d 4 and (c) LS 3d 7 configuration states. A schematic representation of the corresponding MO6 octahedra is also given (b).

Table I. 3 : 6 .Figure I. 6 :

 366 Figure I.6: Representation of the relations between the hexagonal cell and the two possible monoclinic ones. For more clarity the monoclinic cells have been shifted and only the transition metal atoms are represented.

Figure I. 7 :

 7 Figure I.7: Representation of the interslab distance (left) and in plane M-M distances (right) into the orthorhombic and monoclinic structures.

Jahn-

  Teller effect in O'3-NaMnO2 than in O'3-NaNiO2 in agreement with the difference in M-O distances.

  Figure I.8b. Meanwhile, on the negative electrode, the Na + ions are reduced using the extra electrons (e -) provided by the external circuit. The opposite phenomenon happens during the discharge of the battery, as illustrated in Figure I.8c: once the electrical circuit is closed, the transition metals elements at the positive electrode are reduced and the Na + ions are reintercalated. The oxidation of the metallic Na 0 from the negative electrode provides electrons to the electrical circuit.

Figure I. 8 :

 8 Figure I.8: Representation of a Na battery in (a) its initial state and during (b) the charge and (c) the discharge of the cell.

  value (A) t: duration of the (dis)charge (h) F: Faraday's constant = 96485 C.mol -1 Δ*: number of (de)inserted ions +: number of moles of NaxMO2 (mol) in the battery (I.1)

Figure I. 9 :Figure I. 9 :

 99 Figure I.9: Schematic representation of the possible behaviors observed in a galvanostatic cycling.

Figure II. 1 .

 1 The positive and negative electrodes are reposing on stainless steel current collectors. Three layers of Whatman™ glass fiber separators provide a support for the liquid electrolyte absorption and prevent any short circuit due to the dendritic growth from the Na foil. Once assembled, the battery is plugged into a glass container into an Ar filled glovebox to avoid moisture and oxygen contamination outside of the glovebox (visible in Figure II.1b).

Figure II. 1 :

 1 Figure II.1: (a) Schematic representation of the Swagelok™-type cell and (b) picture of a Swagelok™-type battery.

Figure II.2c.Figure II. 2 : 4 . 3 )

 243 Figure II.2: (a) Schematic description of a coin cell, (b) picture of the corresponding parts and (c) top and bottom view of a sealed coin cell.These cells were used for long or precise electrochemical characterizations as they offer more reproducible conditions than the Swagelok™-type cells. Moreover, there is no rotation movement during the assembling which avoids any damage to the positive electrode. The major drawback is that these cells are not recoverable entirely and only the spring and stainless support can be used again after cleaning.

Figure II. 3 :

 3 Figure II.3: Schematic representation of the GITT mode: evolution of the voltage of a Na battery as a function of time.

Figure II. 4 :

 4 Figure II.4: Comparison between the GITT and the galvanostatic curves for two batteries involving the same positive electrode material.

Figure II. 5 :

 5 Figure II.5: Schematic representation of the potentiostatic synthesis route.

  for the Bragg Bentano geometry or for the Debye Sherrer ones [102]. The variances were corrected using the Berar's factor associated to the refinement[103]. E (V vs. Na +

Figure II. 6 .

 6 Figure II.6.

Figure II. 6 :

 6 Figure II.6: Cells used for (left) Panalytical and (right) Bruker diffractometers.

  Mössbauer spectroscopy is a technique commonly used to characterize iron and tin based solid state materials. It is complementary to XRPD as it gives information about the oxidation state and the local environment that XRPD cannot provide. It is based on a physical phenomenon observed in solid state matter evidenced by R. L. Mössbauer: the Mössbauer effect [105, 106]: a Mössbauer source, constituted of an excited element, emits a gamma photon accompanying the nuclear transition from the excited state to the fundamental one (Figure II.7a).

Figure II. 7 :Figure II. 8 :

 78 Figure II.7: Rezoning (a) emission and (b) absorption of a γ photon.

Figure II. 8 . 8 .( 1 )

 881 The chemical shift gives precious information on the oxidation and spin states and the surrounding environment of the Mössbauer probe (Fe or Sn).The quadrupole splitting: ΔThe quadrupole splitting Δ is expressed in mm.s -1 . It is only observed for multiplets and corresponds to the gap between the Mössbauer peaks, as shown in Figure II.The quadrupole splitting is observed only when two conditions are fulfilled: The nucleus must have an angular momentum I > 1/2. The charge distribution in the nucleus is therefore non-spherical and the nucleus possesses an electric quadrupole moment.

Figure II. 9 :

 9 Figure II.9: Quadrupole splitting diagram of the Ie = 3/2 level of an excited 57 Fe nucleus.

= 3/ 2 I

 2 When several Mössbauer sites are involved, populations P are attributed to each site. They can correspond to different materials (phase mixtures), different oxidation states sharing the same (or different) crystallographic sites or to the same oxidation states sharing different crystallographic sites.Data interpretation: fit of the spectrumEvery spectrum is first described by one or several Lorentzian Mössbauer peak(s) in a Lorentzian fit. This step allows refining the chemical shift, the quadrupole splitting and the Full Width at Half Maximum (FWHM) parameters. If the spectrum is too broad, it is possible to fit the spectrum using a distribution fit, which will describe the Mössbauer peaks based on distributions of quadrupole splitting.

  banned. By analogy to in situ XRPD cells, a beryllium window is used as the positive current collector. The negative current collector consisted in a pierced stainless steel piece surrounding a polymer window. To assure the electrical conductivity and the pressure inside the cell, a stainless steel spring terminated by two hollow stainless steel disks was used. The schematic and photographic representations of the cell are given in Figure II.10. The positive electrode consisted in a diameter 13 mm pellet of AM and CB in a 80 :

Figure II. 10 :

 10 Figure II.10: (a) Schematic representation and (b) photography of the Mössbauer in situ cell.

Figure II. 11 Figure II. 11 :(II. 1 )Figure II. 12 :

 1111112 Figure II.11: Transmission of an X-ray beam through a slab of thickness t.

Figure II. 13 :Figure II. 14 :

 1314 Figure II.13: Variation of the absorption through the absorption coefficient as a function of the incident photon energy. Four edges labeled, as K, L1, L2 and L3, are visible in Figure II.13. The same features can be observed before, at and after every edge: (1) the X-ray absorption decreases with the increase of the incident photon energy, (2) a sharp rises appear, corresponding to the edge and (3) the absorption decreases when the incident photon energy increase following a series of oscillations. These phenomenons result from the interactions between the electron wave and the nearby atoms. Usually, the user only focuses on one edge per element. A typical XAS spectrum is shown in Figure II.14.

3 Chapter 1 .

 31 Na x Mn 1-y Fe y O 2 phase diagram(s) with y = 1/3, 1/2 and 2/The NaxMn1-yFeyO2 layered oxides in the literature ............................................................... A-I.2. Synthesis the pristine materials ........................................................................................... A-I.2.a. The aqueous self-combustion type synthesis ...................................................................... A-I.2.b. Synthesis of the pristine materials ...................................................................................... A-I.2.c. Investigation of the NaxMn1-yFeyO2 phase diagrams by self-combustion synthesis ............... A-I.3. Characterization of the pristine materials ............................................................................. A-I.3.a. X-ray powder diffraction analysis ....

Figure A-I. 1

 1 along its Scanning Electron Microscopy (SEM) micrograph.

Figure A-I. 1 :

 1 Figure A-I.1: (a) photography and (b) Scanning Electron Microscopy micrograph of the product of the selfcombustion synthesis of a NaxMn1-yFeyO2 material after grinding.

Figure A-I. 2 :

 2 Figure A-I.2: XRPD pattern and phase identification of the product recovered after the self-combustion synthesis step of the P2-NaxMn2/3Fe1/3O2 phase and before heat treatment.

Figure A-I. 3 .

 3 Figure A-I.3.

Figure A-I. 3 :

 3 Figure A-I.3: Schematic representation of the heat treatment step of the NaxMn1-yFeyO2 materials.

  1 mm diameter capillaries in order to highlight the present phases (Fe2O3, P2, O3 and O'3). The determined phase diagrams are represented in Figure A-I.4.

Figure A-I. 4 : 4 ,

 44 Figure A-I.4: Phase diagrams as a function of the sodium content for the NaxMn2/3Fe1/3O2, NaxMn1/2Fe1/2O2 and NaxMn1/3Fe2/3O2 systems. 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1.0

Figure A-I. 5 .

 5 They exhibit pure P2 and O3 phases except for the Na0.82Mn1/2Fe1/2O2 composition, as predicted (O3+O'3 mixture). The cell parameters and interslab distances of the different materials are reported in Table A-I.1. The structure of each material will be further discussed in their corresponding sections (Chapters A-II and A-III).

Figure A-I. 5 :

 5 Figure A-I.5: Observed and calculated XRPD patterns for (a) the P2-Na0.77Mn2/3Fe1/3O2, (b) the P2-Na0.67Mn1/2Fe1/2O2, (c) the (O3+O'3)Na0.82Mn1/2Fe1/2O2 and (d) the O3-Na0.82Mn1/3Fe2/3O2 phases. Red crosses: observed, black line: calculated, blue line: difference plot and green bars: Bragg reflections. (a, b, d): Rietveld refinement and (c): LeBail profile.

Figure A-I. 6

 6 shows the Scanning Electron Microscopy micrographs corresponding to the P2-Na0.62Mn1/2Fe1/2O2 and O3-Na0.77Mn1/3Fe2/3O2 materials, which are representative of the P2 and O3-NaxMn1-yFeyO2 materials, respectively.

Figure A-I. 6 :

 6 Figure A-I.6: Scanning Electron Microscopy micrographs for (a) the P2-Na0.67Mn1/2Fe1/2O2 and (b) the O3-Na0.82Mn1/3Fe2/3O2 phases.

Figure A-I. 7

 7 shows the first four cycles obtained from the O3-Na0.77Mn1/3Fe2/3O2 phase (starting by a discharge) using the pure NaPF6 in PC (1M) electrolyte (Figure A-I.7a), the NaPF6 in PC (1M) + 2 wt% VC one (Figure A-I.7b) or the NaPF6 in PC (1M) + 2 wt% FEC one (Figure A-I.7c). The first cycle is highlighted in red for all experiments. The corresponding capacity retentions upon cycling are given in Figure A-I.7d.

Figure A-I. 7 :

 7 Figure A-I.7: Galvanostatic cycling curves involving the O3-Na0.77Mn1/3Fe2/3O2 material at the positive electrode recorded between 1.5 and 3.8 V at C/50: (a) without any additive, (b) with the VC electrolyte additive and (c) with the FEC electrolyte additive. The associated discharge capacities are also represented (d).

  0

  Figure A-I.8 shows the evolution of the voltage of the cells as a function of the Na content when cycled between 1.5 and 3.8 V.

Figure A-I. 8 :

 8 Figure A-I.8: Galvanostatic cycling curves of the Na/ NaPF6 in PC (1 M) + 2 wt% FEC /NaxMn1-yFeyO2 cells obtained at a C/50 rate starting by a discharge between 1.5 and 3.8 V. (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 and (d) O3-Na0.77Mn1/3Fe2/3O2. A magnification of each curve around the starting point is shown in the insets.

Figure A-I. 9

 9 compares the evolution of the discharge capacities of the batteries assembled with the various NaxMn1-yFeyO2 materials. The theoretical discharge capacity of the P2 and O3 materials is approximatively equal to 240 mAh.g -1 (considering 1 Na + intercalated per formula unit).

Figure A-I. 9 :

 9 Figure A-I.9: Discharge capacities corresponding to the Na//NaxMn1-yFeyO2 cells cycled between 1.5 and 3.8 V and assembled from the P2-Na0.66Mn2/3Fe1/3O3 (black), P2-Na0.62Mn1/2Fe1/2O2 (blue), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (red) and O3-Na0.77Mn1/3Fe2/3O2 (green) materials.

  x Mn 1/3 Fe 2/3 O 2 Cycle number Discharge capacitiy (mAh.g -1

1 . 1 .

 11 The NaxMn1/3Fe2/3O2 system ................................................................................................ A-II.1.a. Synchrotron X-ray and Neutron powder diffraction studies of the pristine material........... A-II.1.b. Electrochemistry ............................................................................................................... A-II.1.c. In situ XRPD study during Na deintercalation ..................................................................... A-II.1.d. Ex situ Synchrotron X-ray diffraction study of the different structural domains ................. A-II.2. The NaxMn1/2Fe1/2O2 system .............................................................................................. A-II.2.a. Electrochemistry ............................................................................................................. A-II.2.b. Operando in situ XRPD study during Na deintercalation................................................... A-II.2.c. Ex situ Synchrotron X-ray diffraction study of O'3-Na0.95Mn1/2Fe1/2O2 ............................... A-II.3. Study of the redox mechanisms during Na deintercalation for the O3-based NaxMn1/3Fe2/3O2 and NaxMn1/2Fe1/2O2 systems ...................................................................................................... A-II.3.a. Operando in situ X-ray Absorption Near Edge Spectroscopy study ................................... A-II.3.b. 57 Fe Mössbauer spectroscopy study................................................................................. A-II.4. Conclusion on the O3-based NaxMn1-yFeyO2 systems .......................................................... -82-This chapter focuses on the characterization of the O3 pristine materials and the study of their phase diagram along with the Na content. First, the structural and electrochemical properties of O3-Na0.77Mn1/3Fe2/3O2 are investigated. The same investigations are then carried out on (O3+O'3)-Na0.77Mn1/2Fe1/2O2. The last part of this chapter concerns the redox mechanisms associated to the Na deintercalation for both materials. Because of the fluorescence of the Mn and Fe species under the Co and Cu kα radiations, respectively, we carried out synchrotron X-ray powder diffraction (synchrotron XRPD) experiments 8 that achieves very good signal / noise ratio and thus allowed a better structural determination than routine XRPD. The collected synchrotron diffraction pattern of O3-Na0.77Mn1/3Fe2/3O2 and the calculated diagram resulting from the structural Rietveld refinement method are shown in Figure A-II.1. The corresponding cell and atomic parameters are reported in Table A-II.The 2θ scale corresponding to the Cu kα1 radiation is given as a guide.

Figure A-II. 1 :

 1 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.

1 :

 1 Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.The lattice parameters of the hexagonal cell (R-3m space group): ahex. = 2.98195(3) Å and chex. = 16.3420(2) Å are close to those of the literature on the O3-NaMn1/2Fe1/2O2 material (ahex. = 2.9590(6) Å and chex. = 16.522(2) Å[26]). The difference to the values of the ahex. and chex. parameters could result from the different sodium contents between the two materials and the different Mn / Fe ratio. The excellent data quality allowed us to refine the various atomic displacement parameters (ADP), which was impossible from the laboratory XRPD patterns. The total Mn/Fe site occupancy was fixed equal to 1.0 and the ADP value for the transition metal ions refined to 0.47(2) Ų. The occupancy and ADP of the Na + ion are equal to 0.77(1) and 1.3(1) Ų respectively. This high value of the Na + ion ADP can result from the high mobility of

Figure A-II. 2 .

 2 As no superstructure peak appears on the neutron diffraction pattern, we concluded that O3-Na0.77Mn1/3Fe2/3O2 does not exhibit any long-range ordering between the transition metal ions. The structure of the material was then refined from the XRPD and neutron diffraction data using Pseudo-Voigt functions to describe each pattern as shown in Figure A-II.2. The corresponding cell and atomic parameters are given in Table A-II.2. This combined refinement leads to a structure in very good agreement with the structural model obtained from Synchrotron XRPD and gives a final content of 0.68(1) Fe and 0.32(1) Mn, in good agreement with the expected one.

Figure A-II. 2 :

 2 Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.

  λ = 1.59324(4) Å Intensity (A. U.) 2θ (°) Cu kα 1,2

  3.c.) we investigated the impact of the upper voltage cutoff on the electrochemical properties. The cycling curves obtained in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges are given in Figures A-II.3a, A-II.3b and A-II.3c respectively. As previously, the first four cycles are shown, starting by a discharge and the first cycle is highlighted in red. The evolution of the discharge capacity is given in Figure A-II.3d. As one can see, the increase of the upper cutoff voltage above 3.8 V clearly induces an extra capacity for the second discharge (Figure A-II.3d), associated to a higher polarization of the cycling curve. The discharge capacities of the batteries cycled up to 4.0 and 4.3 V are comparable and follow the same decrease tendency toward the values of cell cycled up to 3.8 V, reached approximately after the 14 th cycle. This large decrease of the discharge capacity is visible in Figures A-II.3b and A-II.3c through the decrease of the available Na + ions for (de)insertion.

Figure A-II. 3 :

 3 Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state. To better understand the impact the cut-off voltage has on the material, we realized a series of SEM micrographs on an un-cycled electrode (Figures A-II.4a-b) and on electrodes collected after 50 cycles between 1.5 and 3.8 V (Figures A-II.4c-d), between 1.5 and 4.0 V (Figures A-II.4e-f) and between 1.5 and

  of the discharge capacities

Figure A-II. 4 :

 4 Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.

Figure A-II. 5 :

 5 Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 .

2 Figure A-II. 6 :

 26 Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. Black Miller indexes: O'3 phase.

Figure A-II. 7 :

 7 Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. Black Miller indexes: O'3 phase.

91 -

 91 As it is further detailed, several structural changes occur during the charge. In the almost fully intercalated state a structural distortion (O'3) is observed. The sodium deintercalation leads to the formation of the O3 phase (the pristine one) through a biphasic domain in the 0.85 ≤ x < 0.94 composition range. For x < 0.62 the P3 structure type appears. It exhibits a larger interslab distance due to the prismatic environment of the sodium ions as shown by the (00l)P3 which appears at lower angles. The structural modification is clearly shown by the disappearance of the (104)O3 diffraction peak which is always very weak on the XRPD patterns of P3 phases in comparison with the O3 ones. Surprisingly the O3 type phase does not disappear completely upon charging (Figure A-II.7).

/ 3 for

 3 the O3 and P3 phases or to cmon. sin(β) for O'3. The evolution of the interslab distances and cell parameters are plotted in Figures A-II.9a-b respectively as a function of the Na content. The cycling curve is also represented in Figure A-II.9c as a guide.

Figure A-II. 8 :Figure A-II. 9 :

 89 Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.

  x Mn 1/3 Fe 2/3 O 2 a hex. cell parameter (P3) -94-

Figure A-II. 10 :

 10 Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The red lines highlight the limitations of the solid solutions and / or biphasic domains.

  interslab distance in our material (5.02 Å for x = 0.1) is in agreement with the presence of remaining Na + ions (x = 0.15). More recently, Xu et al. also concluded on the formation of NaO6 octahedra to accompany the deintercalation of P2-Na0.80Li0.12Ni0.22Mn0.66O2 by DFT calculations [70]. In the latter case, an O2 type structure was also obtained from the P2 one. For x < 0.1, a new diffraction line appears at 2θ ≈ 17.3°, indicating that a new biphasic domain or new stacking faults could be expected. However we cannot rely on this information only and more experiments would be needed to confirm this feature. A schematic representation of the NaxMn1/3Fe2/3O2 phase diagram is given in Figure A-II.11.

Figure A-II. 11 :

 11 Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.

Figure A-II. 12 :

 12 Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.

a) First discharge to 1 . 5 V

 15 discharge to 1.5 V -O3-Na ≈0.8 Mn 1/3 Fe 2/3 O 2 (R-3m)

  Figure A-II.13 shows the experimental and calculated synchrotron XRPD patterns for the O'3-type phase. The corresponding cell and atomic parameters are given in Table A-II.3.

Figure A-II. 13 :

 13 Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement.

Figure A-II. 14 :

 14 Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement.

4 :

 4 Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern. The P3-Na0.61Mn1/3Fe2/3O2 phase The sample of the P3 phase was prepared by targeting Eeq = 3.4 V. The Synchrotron XRPD pattern corresponding to the P3 phase is represented in Figure A-II.15 along with the calculated one. The cell and atomic parameters corresponding to this refinement are given in Table A-II.5. The synchrotron XRPD pattern of the P3-type phase is successfully fitted with a small impurity of the O3 phase. In the P3 stacking type, the sodium ion occupies a prismatic NaO6 site which shares a face and three edges with the surrounding MO6 octahedra. This change in coordination results from the gliding of two MO2 planes in the structure whose corresponding O positions move from an "ABCABC" stacking to an "ABBCCA" one. The refinement of the Na content leads to the P3-Na0.61(3)Mn1/3Fe2/3O2 formula. Due to a stronger electrostatic Na + -M 3+/4+ repulsion through the common NaO6 / MO6 face, the sodium ion is slightly off centered in its prismatic environment along the c-direction (zNa = 0.168(1) instead of z = 1/6 if centered) ; separating the Na-O distances into three long (2.49(3) Å) and three short ones (2.41(3) Å). The higher Na + ion diffusion expected in the P3 structure explains the huge decrease of the polarization at the O3 → P3 transiion that we discussed along with the GITT curve (Figure A-II.5). The evolution of the M-O and Na-O distances in MO6 and NaO6 polyhedra of O'3-Na0.96Mn1/3Fe2/3O2, O3-Na2/3Mn1/3Fe2/3O2 and P3-Na0.61Mn1/3Fe2/3O2 phases are represented in Figure A-II.16 along with the evolution of the MO2 slab thicknesses. The evolution of the interlayer space was already discussed with the operando in situ experiment carried out during Na + deintercalation: due to the lowering of the screening effect of the Na + ions on the surrounding oxygen planes, the interslab distance increases during Na + deintercalation for the O'3/O3 and P3 phase domains. Tables A-II.3, A-II.4 and A-II.5 allow calculating the MO2 slab thicknesses for the associated O'3, O3 and P3 materials. Their comparisonshows that lowering the Na + content induces thinner MO2 slabs (from a 2.17(1) Å thickness (x = 0.96) to 2.06(1) (x = 0.61)), due to the increasing amount of M 4+ ions: their smaller ionic radii increase the strength of the M-O bonds, resulting in thinner MO2 slabs.

Figure A-II. 15 :

 15 Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement.

Figure A-II. 16 :

 16 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyhedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.

  the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges are presented in Figure A-II.17a-c, respectively. The first four cycles are represented with the first one is highlighted in red. The evolution of the associated discharge capacities is shown in Figure A-II.17d.

Figure A -

 A Figure A-II.17d. The capacity retentions associated to the 29 th cycle for the different experiments are quite different: 80 %, 91% and 75 % for Ecut-off = 3.8 V, 4.0 V and 4.3 V, respectively. Surprisingly the experiment carried out in the 1.5 -4.0 V range show the best capacity retention.

Figure A-II. 17 :

 17 Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.

Figure

  Figure A-II.18b.

Figure A-II. 18 :

 18 Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.

  by a potentiostatic intercalation at 1.5 V until the current was close to 0 mA. The XRPD pattern was recorded. The battery was then charged at C/100 and the conditions were optimized to record the XRPD patterns in the 13 -20° and 30 -43° 2θ ranges in one hour. Therefore, two successive XRPD patterns should correspond to a sodium step of 0.01 Na + per formula unit. Unfortunately, a huge electrolyte decomposition issue occurred for this experiment as no additive was employed at that time and it is impossible to rely on the x values of the galvanostatic curve. Instead, we plotted the galvanostatic curve as a function of time as shown in Figures A-II.19 and A-II.20 in inverse order. Knowing the potential corresponding to every XRPD pattern, it is possible to give an estimation of the sodium contents by comparison to a galvanostatic curve recorded with the FEC additive. For clarity purpose, only the sodium contents of the structural domain limitations are given.

Figure A-II. 19 :

 19 Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains. Blue Miller indexes: O3 and P3 phases. Black Miller indexes: O'3 phase.

Figure A-II. 20 :

 20 Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains. Blue Miller indexes: O3 and P3 phases. Black Miller indexes: O'3 phase.

4

 4

  As it is further discussed several structural domains are observed during the charge. The almost fully intercalated state exhibits a structural distortion induced by the Mn 3+ ions (O'3 phase). Na + deintercalation leads to the formation of an O3 phase through a biphasic domain (XRPD patterns recorded between the 3 rd and 12 th hours). At the 38 th hour of the experiment (x ≈ 0.70) the P3 phase appears through an O3 + P3 biphasic domain in the 0.55 ≤ x ≤ 0.70 range. Then for x ≤ 0.25, a new phase labeled "X" is observed.As in the NaxMn1/3Fe2/3O2 system, a residual diffraction peak corresponding to the interslab distance remains at 2θ ≈ 16.6° and shifts to lower 2θ values upon deintercalation to x = 0.55. For x < 0.55, the position of the residual diffraction peak shifts towards higher 2θ values. One can suppose the residual diffraction peak corresponds to an O3 phase which is deintercalated without transforming into the P3 one. From the XRPD patterns it was possible to determine the cell parameters by Full Pattern Matching or by the 2θ position of the (00l) and supposedly (012) diffraction lines. The estimated interslab distances and cell parameters are shown in Figure A-II.21 along with the galvanostatic curve.

Figure A-II. 21 :

 21 Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).

  phase a mon. cell parameter (O'3) b mon. cell parameter (O'3) a hex. cell parameter (O3) a hex. cell parameter (P3) E (V) a,b cell parameters (Å)The XRPD pattern of the almost fully intercalated phase, Na0.95Mn1/2Fe1/2O2, can be indexed in the monoclinic system (space group C2/m, O'3 structure). As for O'3-Na0.96Mn1/3Fe2/3O2, the monoclinic distortion is emphasized by the splitting of the (012)hex. and (104)hex. diffraction peaks of the O3 structure to the (-111)mon. + (200)mon. and to the (-202)mon. +(111)mon. ones, respectively (Figures A-II.19 and A-II.20).The high sodium content in this phase decreases the repulsions between the surrounding O planes. This leads to a small interslab value of approximatively 5.37 Å. The O'3 phase is observed alone on a very narrow range as the O3 phase is evidenced at the 3 rd hour of the experiment. The biphasic domain between the O'3 and O3 phases, observed between the 3 rd and 12 th hours of the experiment, corresponds to the voltage plateau observed at ≈ 2.3 V on the GITT cycling curve (Figure A-II.18). The interslab distance of the O3 phase is slightly higher than the O'3 one in the biphasic domain (≈ 5.44 Å vs. ≈ 5.37 Å, cf. Figure A-II.21). This is due to the lower Na amount in the O3 phase which lowers the screening effect on the surrounding O planes. Then, the O3 phase follows a solid solution behavior and its interslab distance continuously increases for the previously stated reason. At the 38 th hour of the experiment (x ≈ 0.70) the P3 phase appears (Figure A-II.19). It is characterized by a larger interslab distance (5.63 Å vs. 5.55 Å for the O3 phase at x ≈ 0.70) induced by the formation of NaO6 prismatic sites. For x < 0.39, the P3 phase disappears while a new (00l) diffraction peak appears at ≈ 17 °. Following our hypothesis previously stated on the

  Figure A-II.22. The first one (green arrow in Figure A-II.22) is similar to the one of the O3* phase observed in the NaxMn1/3Fe2/3O2 system. As for the NaxMn1/3Fe2/3O2 system, we suppose the origin of this intermediate phase to be (i) slight variation of Mn / Fe ratios or (ii) the coexistence of particles with or without Mn vacancies (A-II.1.c). The two other residual diffraction peaks (pink and blue arrows in Figure A-II.22) show a different behavior as they suddenly appear on the XRPD patterns. As for the P3* phase in the NaxMn1/3Fe2/3O2 system, we believe that these diffraction peaks show the apparition of stacking faults in the P3 phase.

Figure A-II. 22 :

 22 Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).

114 -Figure A-II. 23 :

 11423 Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.

  discharge to 1.5 V b) Second discharge to 1.5 V Intensity (A.U.) 2θ (°) Cu kα 1.: C2/m a = 5.400(1) Å b = 2.941(4) Å c = 5.710(1) Å β = 110.30(1) °S.G.: C2/m a = 5.393(2) Å b = 2.943(1) Å c = 5.705(2) Å β = 110.18(1) ° A-II.2.c. Ex situ Synchrotron X-ray diffraction study of O'3-Na0.95Mn1/2Fe1/2O2 In order to better understand the structure of the fully intercalated phase, we prepared a sample of the O'3 phase by the potentiostatic route (Eeq = 1.5 V). This sample was then washed and analyzed by synchrotron XRPD. The experimental and calculated synchrotron XRPD patterns for the intercalated phase are represented in Figure A-II.24. The corresponding cell and atomic parameters are reported in Table A-II.6.

Figure A-II. 24 :

 24 Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement.

1 *O' 3 - 3 .

 133 Na 0.95 Mn 1/2 Fe 1/2 O 2 Space group : C2/m a mon. = 5.4111(8) Å, b mon. = 2.9433(3) Å, c mon. = 5.711(1) Å, β mon. = 110.31(1)°a mon. /b mon. = 1Study of the redox mechanisms during Na deintercalation for the O3-based NaxMn1/3Fe2/3O2 and NaxMn1/2Fe1/2O2 systems We studied the redox mechanisms involved during Na + deintercalation for the two O3-based systems. The open current voltage charge curves extracted from the GITT cyclings shown in Figure A-II.25

Figure A-II. 25 :

 25 Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.

  parts of the spectrum are shown in Figure A-II.26 for the NaxMn1/3Fe2/3O2 (Figures A-II.26a and A-II.26b) and NaxMn1/2Fe1/2O2 (Figures A-II.26c and A-II.26d) compositions. The Mn and Fe K-edges were recorded and are compared to various references, presented in Figures A-II.26e and A-II.26f, respectively.

Figure A-II. 26 :

 26 Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f).

  Fe Mössbauer spectroscopy study of the NaxMn1/3Fe2/3O2 system The Mössbauer spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material was first recorded as shown on top of Figure A-II.27. It exhibits a quadrupole doublet that can be fitted by a Lorentzian profile.The fit of the spectrum necessitates two Fe sites (Table A-II.7). The corresponding isomeric shifts are typical of high spin (HS) Fe 3+ ions in octahedral sites and so the sites were labelled as Fe 3+ (A) and Fe 3+ (B).These two sites are represented by the blue and green lines inFigure A-II.27. The higher value of the quadrupole splitting for the Fe 3+ (A) site (Δ = 0.88 mm.s -1 ) indicates that the local environment of the FeO6octahedron is more impacted by the surrounding disorder than the Fe 3+ (B) site (Δ = 0.58 mm.s -1 ). The populations (P) give a majority of the Fe 3+ (B) site (75%). In the literature, Yabuuchi et al. also used two Fe 3+ sites to fit the spectrum of P2-Na2/3Mn1/2Fe1/2O2[26]. Thorne et al. used two Fe 3+ sites and a Fe 4+ one to fit the spectra of P2/O3-NaxMn1-xFexO2 phases. However, the population of the Fe 4+ in their Mössbauer studies is inferior to 2 % for most of the materials[28].We then conducted the in situ Mössbauer study. The spectra of the NaxMn1/3Fe2/3O2 phases were recorded for selected sodium contents: x = 0.96, 0.85, 0.67, 0.58 and 0.38 during charge, following an initial discharge, and after a negligible residual current was observed for each composition. The recorded spectra are shown in Figure A-II.27b. As one can see, there is no significant variation of the peak positions for 0.96 ≥ x ≥ 0.67 as highlighted in Figure A-II.28a. On the opposite, there is a significant shift of the peak positions to lower velocity values for x ≤ 0.58 as highlighted in Figure A-II.28b. This indicates a change in the oxidation state of the Fe 3+ ions. As for the pristine material, all spectra exhibit a quadrupole doublet whose asymmetry and FWHM increase as sodium is removed from the structure (Figure A-II.27b).

Figure A-II. 27 :

 27 Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Black circles: experimental and red lines: calculated.

Figure A-II. 28 :

 28 Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (green line) and x = 0.38 (pink line) compositions.

  second calculation has been realized based on fixed isomer shifts deduced from the Lorentzian profile type refinement. The FWHM values have been fixed to 0.20 for the x = 0.96 and 0.85 samples; 0.25 for the x = 0.67 sample and 0.30 for the x = 0.58 and 0.38 ones to take into account the increasing disorder in the material. From these distribution fittings, we determined the average quadrupole splitting (Δ*) and the population of the different iron sites which are presented in Table A-II.8 along with the developed formula and awaited Fe n+ populations. The quadrupole splitting of the maxima of the distribution (Δmax) is also given.

Fe

  4+ ratio equal to 95 : 5 (x = 0.44) and 68 : 32 (x = 0.22) and confirm the increasing amount of Fe 4+ in the material upon Na + deintercalation. The difference between the formulae determined by Mössbauer spectroscopy (Na0.47Mn1/2Fe1/2O2 and Na0.32Mn1/2Fe1/2O2, respectively) and the ones determined by electrochemistry (Na0.44Mn1/2Fe1/2O2 and Na0.22Mn1/2Fe1/2O2, respectively) may result from an underestimation of the Na content, which lead to an overestimation of the Fe 4+ one in the formulae determined from electrochemistry.

Figure A-II. 29 :

 29 Figure A-II.29: 57 Fe Mössbauer spectra recorded ex situ for the NaxMn1/2Fe1/2O2 system at the (a) x = 0.95, (b) x = 0.67, (c) x = 0.55, (d) x = 0.44 and (e) x = 0.22 compositions. Black circles: experimental and red lines: calculated. The different Mössbauer sites deduced from the Lorentzian fittings are represented by the blue, pink and green lines.

  pattern of the P2-Na0.67Mn1/2Fe1/2O2 pristine material is shown in Figure A-III.1 along with the calculated diagram resulting from the Rietveld refinement of the structure. The cell and atomic parameters corresponding to the Rietveld refinement are reported in Table A-III.1. The 2θ scale corresponding to the Cu kα1 radiation is given as a guide.

Figure A-III. 1 :

 1 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.

Figure A-III. 2 . 2 . 2 .

 222 As no superstructure peak appears on the neutron diffraction pattern, we concluded that P2-Na0.62Mn1/2Fe1/2O2 does not exhibit any long-range ordering between the transition metal ions. The structure of the material is refined from the XRPD and neutron diffraction data using Pseudo-Voigt functions to describe each pattern as shown in Figure A-III.The corresponding cell and atomic parameters are given in Table A-III.This combined refinement leads to a structure in very good agreement with the structural model obtained from synchrotron XRPD and gives a final content of 0.500(1) Fe and 0.500(1) Mn, in good agreement with the expected Mn : Fe ratio. The sodium content is equal to 0.60 and is very close to the one deduced by synchrotron XRPD (x = 0.62).

Figure A-III. 2 :

 2 Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.

  electrochemical properties of P2-Na0.62Mn1/2Fe1/2O2 as a positive electrode material in Na cells were studied in various potential ranges at C/20: 1.5 -3.8 V (Figure A-III.3a-b), 1.5 -4.0 V (Figure A-III.3cd) and 1.5 -4.3 V (Figures A-III.3e-f). The experiments started by a discharge and the first cycles are highlighted in red in Figures A-III.3a, A-III.3c and A-III.3e. The evolution of the shape of the E = f(x) curves at the 1 st , 25 th and 50 th cycles are shown in Figures A-III.3b, A-III.3d and A-III.3f.

Figure A-III. 3 :

 3 Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.

  Figures A-III.3b, A-III.3d and A-III.3f. When the cut-off voltage is set to 3.8 V (Figure A-III.3a-b) or 4.0 V (Figure A-III.3c-d), the 25 th and 50 th cycles do not show any significant evolution compared to the first cycle followed by the second discharge (the initial discharge is not considered), besides a progressive decrease of the capacity and a small increase of the polarization. On the other hand, when the cut-off voltage is set to 4.3 V (Figure A-III.3e-f), the shape of the cycling curves exhibit drastic evolutions upon cycling: i) the polarization of the curve increases, ii) a smoothing of the voltage jump at x = 0.5 is observed and iii) the 2 nd plateau observed at ≈ 3.3 V in discharge decreases in length (x) at the 25 th cycle and disappears at the 50 th cycle. These changes in behavior result in a strong decrease of the capacity upon cycling: while 0.70 Na + ions per formula unit are reintercalated between the first charge and the second discharge, only 0.52 and 0.44 Na + ions are reversibly cycled in the 25 th and 50 th cycles respectively.

Figure A-III. 4 : 1 ,Figure A-III. 5 :

 415 Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3).Whereas the second cycle discharge capacities increase with the upper cut-off voltage (120 mAh.g -

Figure A-III. 6 Figure A-III. 6 :

 66 Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.

Figure A-III. 7 .Figure A-III. 7 : 7 .

 777 Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 .

  Figure A-III.8.

Figure A-III. 8 :

 8 Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.

Figure A-III. 9 :

 9 Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.

Figure A-III. 10 :

 10 Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.

4

 4

For x ≤ 0

 0 .95, a second phase is formed (Figure A-III.9). It is clearly visible with the appearance of two diffraction peaks at approximately 16.3° and 32.6° that correspond to the (002)P2 and (004)P2 reflections in the hexagonal cell (P2 type structure), respectively. The biphasic domain between the P2 and P'2 phases is observed for a Na content comprised between 0.85 < x ≤ 0.95. Upon further charging, only a single phase with P2 type structure is present down to x ≈ 0.35. For 0.25 < x ≤ 0.35 the intensity of the P2 diffraction lines decreases (Figure A-III.10). Simultaneously, a broadening of the (002)P2 diffraction peak is observed on the high angle side and a new diffraction peak appears in the 16.7 ≤ 2θ ≤ 16.9 ° region. This behavior is very similar to the one observed in Chapter A-II for the O3-based systems at the end of charge. We assume that stacking faults consisting in layers of NaO6 octahedrons are created among the P2 layers in the material for 0.25 < x ≤ 0.35. For x < 0.25, only one diffraction lines is observed in 15.3 -18.1 ° 2θ range, indicating that only one stacking prevails. The important broadening supposes a loss in the long-range order of the material. An indexation of the XRPD

  2 + borth.2 )/2. The variation of the interslab distance is reported in Figure A-III.11a while the variation of the ahex., aorth. and borth. cell parameters (P2 and P'2 phases) or of the M-M distance ("Z" phase) are reported in Figure A-III.11b. The main feature concerns the interslab distance which increases continuously for the P2 type, then it decreases when the "Z" phase is formed.

Figure A-III. 11 :

 11 Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).

  accommodate this interslab thickness contraction and to decrease the O-O repulsions, a shift of the slab occurs with formation of octahedral sites in the interslab space. Upon deintercalation, the M-M distance decreases continuously as a result of the transition metal oxidation. The second important feature concerns the P'2 type phase and is highlighted by two distinct in plane M-M distances of approximately 2.93 and 3.07 Å (Figure A-III.11b). This huge difference in distance implies that the triangular lattice formed by Mn and Fe atoms is highly distorted. After the operando in situ XRPD experiment and the charge up to 4.3 V, the cell was discharged again down to 1.5 V and maintained at this voltage until a negligible residual current was observed. The XRPD pattern recorded after this second discharge is compared to the one recorded after the first discharge in Figure A-III.12.

Figure A-III. 12 :

 12 Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.

Figure A-III. 13 :

 13 Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement.

  Figure A-III.14. The ADP value for the Na + ions in the P'2 phase is lower (0.7(2) Ų) than for those of the P2-Na0.62Mn1/2Fe1/2O2 phase (1.9(3) Ų), in agreement with the fact that the Na + ions should be much less mobile for a stoichiometry close to Na1Mn1/2Fe1/2O2.

Figure A-III. 14 :

 14 Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.

  of P2-Na0.77Mn2/3Fe1/3O2 is shown in Figure A-III.15 along with the calculated pattern (Rietveld method). The corresponding cell and atomic parameters are reported in Table A-III.4.

Figure A-III. 15 :

 15 Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.

Figure A-III. 16 .

 16 The atomic and cell parameters deduced from the Rietveld refinements of the structure are given in TableA-III.5.

Figure A-III. 16 :

 16 Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol on the neutron powder diffraction pattern indicates a diffraction peak from the vanadium sample container.

  Na0.66Mn2/3Fe1/3O2 as a positive electrode material for Na batteries, we carried out several electrochemical characterizations including cycling into various voltage ranges. The galvanostatic E = f(x) curves obtained in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges are given in Figures A-III.17a-c, respectively with the first cycle highlighted in red. The evolution of the discharge capacities along with the cycle number is reported in Figure A-III.17d.

Figure A-III. 17 :

 17 Figure A-III.17: Galvanostatic cycling curves associated to the NaxMn2/3Fe1/3O2 system and recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/20. (d) Associated discharge capacities. The capacities of the first cycle are not shown in (d) as they correspond to the partially intercalated state.

1 ( 1 . 5 - 3 . 8 V

 11538 Figure A-III.17d. Logically,the increase of the upper cut-off voltage induces an extra capacity for the second cycle from 140 mAh.g -) to 152 mAh.g -1 (1.5 -4.0 V) or 178 mAh.g -1 (1.5 -4.3 V). If the discharge capacity retention at the 50 th cycle are comparable for the experiments carried out in the 1.5 -3.8 V and 1.5 -4.0 V ranges (86 and 82%, respectively), increasing cycling in the 1.5 -4.3 V range leads to poor capacity retention (66%) after 50 cycles. We can observe that the discharge capacities in the 1.5 -4.0 V and 1.5 -4.3 V range experiments are identical at the 37 th cycle. The discharge capacity of the 1.5 -4.3 V experiment then continues to decrease and matches the discharge capacity value of the battery cycled up to 3.8 V at the 46 th cycle.

  Figure A-III.18a. For comparison purposes, the GITT cycling curve of the NaxMn1/2Fe1/2O2 material is given in Figure A-III.18b. Starting with a discharge from x = 0.66, the material exhibits a plateau at low voltage for 0.76 ≤ x < 0.88. The same plateau is then observed in charge, confirming the reversibility of the process. Upon further Na deintercalation the voltage continuously increases until a second plateau is observed for 0.22 ≤ x ≤ 0.27. This second plateau is accompanied by an increase of the cell polarization. Deintercalation down to x = 0.13 is accompanied by a continuous voltage increase. Looking closely at the GITT cycling curve during charge, one can see slight slope variation at x ≈ 2/3 and x ≈ 1/2 (red arrows in Figure A-III.18a).

Figure A-III. 18 :

 18 Figure A-III.18: GITT cycling curve recorded with steps of ≈ 0.01 Na + per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the NaxMn2/3Fe1/3O2 system (a). The red arrows indicate slight variation in the slope of the curve. The GITT cycling curve recorded for the NaxMn1/2Fe1/2O2 system is given in (b) as a comparison.

Figure A-III. 20 :

 20 Figure A-III.20: (a) XRPD patterns of the NaxMn2/3Fe1/3O2 material recorded in situ (operando mode) during the charge of a NaxMn2/3Fe1/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding cycling curve. The red XRPD patterns correspond to the limits of the different structural domains.

Figure A-III. 21 :

 21 Figure A-III.21: Inversed representation of the operando in situ XRPD experiment carried out on the NaxMn2/3Fe1/3O2 system: (a) XRPD patterns and (b) corresponding cycling curve. The red XRPD patterns correspond to the limits of the different structural domains.

4

 4

  .20 and A-III.21 allows an estimation of the interslab distances and cell parameters of the different phases. These distances are shown in Figure A-III.22a (interslab distances) and A-III.22b (cell parameters), along with the galvanostatic curve (Figure A-III.22c). The evolution of the interslab distances (Figure A-III.22a) does not show any significant variation in the intermediate P'2i phase + intercalated P'2f phase biphasic domain (0.76 < x ≤ 0.96). The comparison of the cell parameters for the P'2 phases show that the intercalated one is more distorted, as the two M-M distances in the MO2 slabs are approximatively equal to 2.91 and 3.10 Å vs. 2.90 Å and 2.99 Å in the intermediate P'2i phase. This is due to the higher Mn 3+ content of the intercalated P'2f phase which leads to an increase of the cooperative Jahn Teller effect. The lower interslab distance of the intercalated P2 phase (5.40 Å vs. 5.45 Å for the intermediate P'2i phase) confirms this assumption as it implies a higher Na + -and thus Mn 3+ -content. In the intermediate P'2i phase + P2 phase biphasic domain, the two phases share identical interslab distance, in agreement with the observation of the (00l) diffraction lines (Figures A-III.20 and A-III.21). As already discussed, in the P2 solid solution domain the interslab distance continuously increases as Na + ions are involved in the screening effect between the O planes. On the other hand the value of the ahex. cell parameter continuously decreases, due to the contraction of the MO6 octahedra upon the M 3+ → M 4+

Figure A-III. 22 :

 22 Figure A-III.22: Evolution of the (a) interslab distance and (b) a and b cell parameters of the different NaxMn2/3Fe1/3O2 phases upon sodium deintercalation. The galvanostatic curve versus x is also shown as a guide in (c).

  b orth. cell param. (fully-inter. P'2 f ) a orth. cell param. (fully-inter. P'2 f ) b orth. cell param. (intermediate P'2 i ) a orth. cell param. (intermediate P'2 i ) a hex. cell param. (P2) intermediate P'2 i intermediate P'2 i + fully-intercalated P'2 f P2 phase x in Na x Mn 2/3 Fe 1/3 O 2 -164-After the operando in situ experiment, the cell was discharged again down to 1.5 V and the voltage was maintained until a negligible residual current was observed. The XRPD pattern was then recorded under constant voltage, and is compared to the one recorded after the first discharge in Figure A-III.23.

Figure A-III. 23 :

 23 Figure A-III.23: Comparison of the XRPD patterns recorded for the P'2-NaxMn2/3Fe1/3O2 phases after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.

  in the operando mode at low voltage (formation of the P'2 intermediate phase). Current pulses (C/50) corresponding to a sodium step of + 0.03 Na + ions per formula unit were applied. An open current voltage (or relaxation) period was then set for 5 hours in order to reach equilibrium. The XRPD pattern was recorded during the last 90 minutes of the relaxation period between 15° and 45° (2θ Cu kα1). The collected XRPD patterns are shown in Figure A-III.24 along with the GITT curve. A magnification in the 30° -45° 2θ region is given in Figure A-III.25.

Figure A-III. 24 :

 24 Figure A-III.24: (a) XRPD patterns recorded in situ during the relaxation periods of a NaxMn2/3Fe1/3O2/NaPF6 in PC (1M) + 2 wt% FEC /Na cell along with (b) the corresponding GITT curve. Only the most important reflections are labeled for clarity purposes.

Figure A-III. 25 :

 25 Figure A-III.25: (a) Zoom in the 30 -45 ° region of the XRPD patterns recorded in situ during the relaxation periods of a NaxMn2/3Fe1/3O2/NaPF6 in PC (1M) + 2 wt% FEC /Na cell along with (b) the corresponding GITT curve. Only the most important reflections are labeled for clarity purposes.

P

  P'2f : reflections of the intercalated P'2f phase (hkl) P'2i : reflections of the intermediate P'2i phase (hkl) P2 : reflections of the P2 phase P2 a small amount of Na from the pristine material (x = 0.66) leads to the apparition of the intermediate P'2i phase at x = 0.69. The intermediate P'2i phase and P2 phase are observed simultaneously for 0.69 ≤ x < 0.75. At x = 0.75, the intermediate P'2i phase is observed alone.Further intercalation leads to the formation of the fully-intercalated P'2f phase and the biphasic domain between the two P'2 phases is observed in the 0.78 < x < 0.96 range. Then, for x ≥ 0.96, the fullyintercalated P'2f phase is observed alone. The refinement of the XRPD patterns allows determining the interslab distances and cell parameters, as shown in Figure A-III.26. As one can see, the interslab distances of the P2 and intermediate P'2i phase decreases upon Na + intercalation, indicating that both phases are involved in a solid solution process in this limited composition domain. This feature could not be observed on the in situ operando experiment or in the GITT curve (Figure A-III.18a). The interslab distance of both phases does not evolve much upon Na intercalation, indicating equilibrium between the intermediate P'2i and fully-intercalated P'2f phases. Then, the fully-intercalated P'2f phase is observed alone for x = 0.98. Looking closely on the GITT curves in Figures A-III.24b and A-III.25b, we notice two voltage plateaus. The first one is located at E ≈ 2.25 V (0.66 < x ≤ 0.69) and the second one at E ≈ 2.17 V (0.81 ≤ x ≤ 0.93). Due to the small gap between the two voltage plateaus, we do not expect the intermediate P'2i phase (Eeq ≈ 2.20 V) to exhibit important thermodynamic stability.

Figure A-III. 26 :

 26 Figure A-III.26: Evolution of the (a) interslab distance and (b) a and b cell parameters of the P2 and P'2-NaxMn2/3Fe1/3O2 phases upon sodium intercalation. The GITT E = f(x) curve is also shown as a guide in (c).

Figure A-III. 27 :

 27 Figure A-III.27: Observed and calculated (Rietveld method) XRPD patterns of the intercalated P'2-Na0.96Mn2/3Fe1/3O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the position of the graphite diffraction lines.

3 .

 3 = 2.9109(7) Å, b orth. = 5.467(2) Å, c orth. = 10.817(3) Å b orth. /a orth. = 1Study of the Redox mechanisms during Na deintercalation for the P2-based NaxMn1/2Fe1/2O2 and NaxMn2/3Fe1/3O2 systems As for the O3-based systems, we studied the redox mechanisms involved during Na + deintercalation for both P2-based systems. The open current voltage charge curves extracted from the GITT cycling ones are shown in Figure A-III.28. If the voltage jump is located at x ≈ 0.50 on the cycling curve of the NaxMn1/2Fe1/2O2 system (Figure A-III.28), no well-defined voltage jump is observed on the NaxMn2/3Fe1/3O2 curve, preventing any comparison. By comparison to the O3-based systems we expect theMn 4+ /Mn 3+ redox couple to be active in the low voltage region and the Fe 4+ /Fe 3+ redox couple to be active in the high voltage region. To confirm this assumption, we carried out operando in situ X-ray absorption spectroscopy on the NaxMn1/2Fe1/2O2 system only and ex situ57 Fe Mössbauer spectroscopy measurements on the NaxMn1/2Fe1/2O2 and NaxMn2/3Fe1/3O2 systems.

Figure A-III. 28 :

 28 Figure A-III.28: Open current voltage charging curves extracted from the GITT cycling cones for (blue) NaxMn1/2Fe1/2O2 and (red) NaxMn2/3Fe1/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.

  Figures A-III.29a (Mn K-edge) and A-III.29b (Fe Kedge). The spectrum of the Mn and Fe references are shown in Figures A-III.29c and A-III.29d, respectively.

Figure A-III. 29 :

 29 Figure A-III.29: X-ray absorption near edge spectroscopy spectra recorded in situ and corresponding to the (a) Mn and (b) Fe K-edges of a NaxMn1/2Fe1/2O2 electrode. The spectra of the (c) Mn and (d) Fe references compounds are also given. As shown in Figure A-III.29a, the Mn K-edge exhibits an important shift towards higher energies upon deintercalation in the 0.87 ≥ x > 0.47 range. The comparison to the Mn references (Figure A-III.29c)

  Figure A-III.30. The Mössbauer parameters corresponding to the fit of the spectrum are given in Table A-III.7. The spectrum corresponds to a quadrupole doublet whose isomeric shift (δFe3+ = 0.356 mm.s -1 ) is typical of high spin Fe 3+ ions in octahedral sites. The Lorentzian fit (Figure A-III.30a) highlight a quite high FWHM value (Γ = 0.35 mm.s -1 ) and a high quadrupole splitting (ΔFe3+ = 0.67 mm.s -1 ). A distribution fit (Figure A-III.30b) based on fixed isomeric shift and FWHM values (Table A-III.7b) highlight the existence of a distribution of the quadrupole splittings (Δ*) which are too close to be separated (Figure A-III.30c

Figure A-III. 30 :

 30 Figure A-III.30: (a) Lorentzian and (b) distribution fits of the Mössbauer spectrum of the P2-Na0.62Mn1/2Fe1/2O2 pristine material. (c) Distribution profile corresponding to the distribution fit.

24 (

 24 Then several NaxMn1/2Fe1/2O2 materials were prepared following the potentiostatic route in order to obtain precise sodium contents: x ≈ 1.0 (Eeq = 1.5 V), x = 0.5 (Eeq = 3.2 V), x = 0.45 (Eeq = 3.8 V), x = 0.Eeq = 4.0 V) and x = 0.14 (Eeq = 4.3 V). The corresponding Mössbauer spectra are shown in Figure A-III.31 and compared altogether in Figure A-III.32. The developed formulas and awaited Fe n+ populations of the (dis)charged materials are given in Table A-III.8 along with the Mössbauer parameters of the fit of the spectra.

Figure A-III. 31 :

 31 Figure A-III.31: 57 Fe Mössbauer spectra of (a) P'2-Na≈1Mn1/2Fe1/2O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) P2-Na0.5Mn1/2Fe1/2O2, (d) P2-Na0.45Mn1/2Fe1/2O2, (e) "Z"-Na0.24Mn1/2Fe1/2O2 and (f) "Z"-Na0.14Mn1/2Fe1/2O2. Black circles: experimental and red line: calculated. Blue, pink, green and brown lines: 57 Fe Mössbauer sites (Lorentzian fits only).

1 ) 1 ,

 11 Figure A-III.31a) is characterized by a very broadquadrupole doublet which can be described by three Mössbauer sites in a Lorentzian fit. The isomer shifts of these three sites are really close (δFe3+(A) = 0.363 mm.s -1 , δFe3+(B) = 0.366 mm.s -1 and δFe3+(C) = 0.367 mm.s - and correspond to Fe 3+ ions in octahedral sites. If their FWHM values are also similar and approximatively equal to 0.31 mm.s -1 , the three sites show important disparities in their quadrupole splitting values (ΔFe3+(A) = 0.66 mm.s -1 , ΔFe3+(B) = 1.33 mm.s -1 and ΔFe3+(C) = 1.01 mm.s -1 , respectively). These disparities imply that some FeO6 octahedra are located in a much distorted environment, resulting from the cooperative Jahn-Teller effect of the Mn 3+ ions.The spectrum of P2-Na0.50Mn1/2Fe1/2O2 (Figure A-III.31c) also requires three quadrupole doublets to be described. They exhibit smaller isomeric shifts that for the intercalated material (δFe3+(A) = 0.346 mm.s - δFe3+(B) = 0.350 mm.s -1 and δFe3+(C) = 0.358 mm.s -1 ) in agreement with the increase of the average Mn oxidation state from +III to +IV. The disappearance of the Mn 3+ ions and of the cooperative Jahn-Teller effect lowers the distortion of the FeO6 octahedra, as shown by the decreasing average FWHM (Γ ≈ 27.3 mm.s -1 ) and quadrupole splitting of the different sites (ΔFe3+(A) = 1.02 mm.s -1 , ΔFe3+(B) = 0.81 mm.s -1 and ΔFe3+(C) = 0.59 mm.s -1 , respectively).

  14) correspond to an unknown part of the phase diagram where the "Z" phase appears and where a strange phenomenon involving a lot of energy is evidenced on the galvanostatic curve (Chapter A-III.1.b). As the experimental Fe 3+ : Fe 4+ ratio does not evolve much between the samples prepared at 4.0 V (xth. = 0.24) and 4.3 V (xth. = 0.14), one can also suppose the participation of another redox couple for E > 4.0 V. Further experiments are required before we can conclude on this topic.

9 :Figure A-III. 33 :

 933 Figure A-III.33: (a) Lorentzian and (b) distribution fits of the Mössbauer spectrum of the P2-Na0.66Mn2/3Fe1/3O2 pristine material. (c) Distribution profile corresponding to the distribution fit.

Finally, P' 2 -

 2 Na0.96Mn2/3Fe1/3O2 and Na0.26Mn2/3Fe1/3O2 materials were prepared by the potentiostatic route (Eeq = 1.5 V and 4.3 V, respectively) and their spectra were collected as shown in Figure A-III.34. The developed formulas and awaited Fe n+ populations of the (dis)charged materials are given in Table A-III.10 along with the Mössbauer parameters of the fit of the spectra.

Figure A-III. 34 :

 34 Figure A-III.34: 57 Fe Mössbauer spectra of (a) P'2-Na0.96Mn2/3Fe1/3O2, (b) Na0.26Mn2/3Fe1/3O2. Black circles: experimental and red line: calculated.

Figure A-IV. 1 :

 1 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.

Figure A-IV. 2 :

 2 Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges at C/50.

Figure A-IV. 3 : 2 Figure A-IV. 4 :

 324 Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).

  Figure A-IV.5.

Figure A-IV. 5 :

 5 Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.

  Chapters A-I to A-III highlight the existence of a plateau at low voltage that the operando in situ XRPD studies carried out during the charge of Na cells associated to biphasic domains involving the undistorted (O3/P2) distorted phases (O'3/P'2). The origin of the distorted phases for the almost fully intercalated states is attributed to the Jahn-Teller active Mn 3+ ions. From the in situ experiments, we also established the phase diagrams for every system as compared in Figure A-IV.6.

Figure A-IV. 6 :

 6 Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).

Figure A-IV. 7 :

 7 Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.

Figure A-IV. 8 :

 8 Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-yFeyO2 materials. O3-NaFeO2: data from[35], O'3-NaMnO2: data from[44].

Figure A-IV. 9 :

 9 Figure A-IV.9: Evolution of the M-O distances in the MO6 octahedra in P'2 and O'3-Na≈1Mn1-yFeyO2 phases. O'3-NaMnO2: data from [44].

3 - 2 .Figure B-I. 2 :

 322 Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m).

2 : 3 .

 23 Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns. B-I.3.b. Morphology: Scanning Electron Microscopy The various samples were then analyzed by Scanning Electron Microscopy. The resulting micrographs are given in Figure B-I.The SEM micrographs show that the sample involving an excess Na content and heated during 15 hours (Figure B-I.3a) exhibits the largest particles with well-defined shape whose sizes are comprised between 500 nm and 1.50 µm. Several imperfections are observed at the surface of the material and probably correspond to Na salts or un-reacted Na oxides due to the 10 wt% Na excess used. They are not observed on the XRPD pattern and represent a clear minority of the sample. The sample heated during 15 hours with no Na excess (Figure B-I.3b) exhibits smaller grains whose sizes are comprised between 250 nm and 650 nm. Contrarily to the "large grains" sample, no noticeable imperfections are observed at the surface of the material which still exhibits well-defined particles. As commonly observed the excess Na amount facilitates the particle growth in the "large grains" sample. Finally, the sample prepared through a 3 hours heat-treatment (Figure B-I.3c) is characterized by poorly-defined and small particles (≈ 100 nm) which are agglomerated (1 -2 µm). No imperfections are observed at the surface of this material either.Sample a mon. (Å) b mon. (Å) c mon. (Å) β mon. (°) a mon. /b mon.

Figure B-I. 3 : 4 . 3 .

 343 Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.

Figure B-I. 4 :Table B-I. 3 :

 43 Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Red crosses: observed, black line: calculated, blue line: difference and green bars: Bragg positions.

2

 2 Figure B-I.5 for the large (Figure B-I.5a), medium (Figure B-I.5b) and small (Figure B-I.5c) grains samples.

Figure B-I. 5 :

 5 Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in(d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.

  retention (medium grains)

Figure B-I. 3 )

 3 and the purity (see XRPD patterns in Figure B-I.2).

Figure B-I. 6 :

 6 Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).

7 .Figure B-I. 7 :

 77 Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.

8 . 3 (Figure B-I. 8 :

 838 Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.

Figure B-I. 9 :

 9 Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.

55 Figure B-I. 10 :

 5510 Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".

Figure

For 2 /

 2 5 < x < 1/2, the (001)mon. diffraction line shows an important broadening. A zoom of the (001)mon. diffraction peak position of the XRPD patterns around the 2/5 ≤ x ≤ 1/2 range is given in Figure B-I.11.

Figure B-I. 11 :

 11 Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.

  18 (x = 1/2) to #20, the deintercalation from P''3-Na1/2NiO2 prevails, and the interslab distance of the material increases. From patterns #20 to #21, the deintercalation and the creation of stacking faults compensate each other and no variation of the interslab is observed. The broader (001) diffraction peak in pattern #21 involve the increase of the stacking fault amount. From pattern #21 to# 22, the formation of NaO6 octahedral slabs is prevailing and the interslab distance decreases as more and more sodium ions are located in octahedral environments. The coexistence of prismatic and octahedral environments of the Na + ions is the origin of the broadening of the diffraction peak for 2/5 < x < 1/2 range. From x = 2/5 (pattern #22), all sodium ions are located in NaO6 octahedrons and the interslab distance decreases. Upon further deintercalation, the material goes through a solid solution process and the interslab distance increases down to x = 1/3, in agreement with lower sodium content.Looking closely at the XRPD patterns in the 17 -30° 2θ range, we observe the reversible appearance of extra diffraction peaks of lower intensity. This feature is highlighted in Figure B-I.12 which displays the XRPD patterns recorded for x = 1, 0.8, 2/3, 1/2 and 1/3 in the 15 -35° 2θ domain.

Figure B-I. 12 :

 12 Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.

3 Figure B-I. 13 :

 313 Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".

Figure B-I. 14 :

 14 Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples.

  as shown in Figure B-I.15.

  and (-202) diffraction peaks of weak intensity while the (201) and (-112) diffraction peaks show strong intensity. The opposite phenomenon is observed on the XRPD patterns of O'3 structures which show (111) and (-202) diffraction peaks of strong intensity while the (201) and (-112) diffraction peaks show weak intensity. Looking at the (111), (-202), (201) and (-112) diffraction peaks on the synchrotron XRPD patterns (see black Miller indexes in grey areas of Figure B-I.15), we are able to confirm the structures of the peculiar compositions: P'3-Na2/3NiO2, P''3-Na1/2NiO2 and O''3-Na2/5NiO2. Unfortunately, we could not prepare a sample of O'''3-Na1/3NiO2 on time for the synchrotron experiment. However, it is possible to confirm the O'3 stacking in this material looking at the in situ XRPD pattern in Figure B-I.8 as the (111) and (-202) diffraction peaks (42 ≤ 2θ ≤ 45°) exhibit high intensity similar to those of O''3-Na2/5NiO2.

  one possible space group to fit the pattern. The result of the LeBail refinement of the profiles considering the supercell are displayed in Figure B-I.15 for P'3-Na2/3NiO2, P''3-Na1/2NiO2 and O''3-Na2/5NiO2. The space groups and cell parameters of the supercells are given in

4 : 5 :Figure B-I. 15 :

 4515 Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak. Black Miller indexes: subcell indexation. Blue Miller indexes: indexation of the superstructure peaks in the supercell.

5 ,

 5 the supercell of every material necessitates multiplying the bsub. cell parameter. The asub./bsub. ratio is close to √3 (≈ 1.73). Therefore, no cooperative Jahn-Teller effect induced by the Ni 3+ ions is expected. As all materials contain a significant amount of Ni 4+ ions, one can assume that electronic transfer occurs between the Ni 3+ and Ni 4+ ions, preventing from the cooperative distortion of the cell. Electrical measurements are in progress to confirm this hypothesis.The Na≈0.8NiO2 phaseAs highlighted inFigure B-I.16 the XRPD pattern of the Na≈0.8NiO2 phase does not exhibits any weaker reflection in the 15 -35° 2θ range. On the other hand, it presents several extra reflections apparently arising from the splitting of the monoclinic symmetry diffraction peaks of O'3-NaNiO2 and a triclinic symmetry is therefore awaited. However, any attempt to index this diagram failed, in part due to

Figure B-I. 16 :

 16 Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure R. 3 :

 3 Figure R.3 : Micrographes (MEB) des phases (a) P2-Na0.67Mn1/2Fe1/2O2 et (b) O3-Na0.82Mn1/3Fe2/3O2.

L 4 .Figure R. 4 :

 44 Figure R.4 : Courbes de cyclage galvanostatique (C/50) de batteries enregistrées entre 1.5 et 3.8 V : (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 et (d) O3-Na0.77Mn1/3Fe2/3O2. Un agrandissement autour du point de départ est donné pour chacune des courbes.Les mêmes comportements ont été observés que la batterie commence par une charge ou par une décharge et seules les courbes commençant par une décharge sont montrées ici. Pour chaque matériau, les courbes de charge et de décharge sont similaires, indiquant la réversibilité de la (dés)intercalation. Les différentes courbes montrent les mêmes tendances : lors de la première décharge, un plateau en potentiel apparaît et indique un domaine biphasé avec la phase la plus intercalée. Le potentiel de ce plateau est supérieur de 0.2 V pour les phases de type O3 par rapport aux phases de type P2. Cela indique qu'une plus grande énergie est nécessaire pour (dés)intercaler les ions Na + dans les phases de type O3.

Figure R. 5

 5 pour les différents matériaux.

Figure R. 5 :

 5 Figure R.5 : Capacités en décharge extraites des courbes galvanostatiques (Figure R.4) : P2-Na0.66Mn2/3Fe1/3O3 (noir), P2-Na0.62Mn1/2Fe1/2O2 (bleu), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (rouge) et O3-Na0.77Mn1/3Fe2/3O2 (vert).

1 )Figure R. 6 :

 16 Figure R.6 : (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante.

Figure R. 7 :

 7 Figure R.7 : Représentation inverse de la Figure R.6. (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante.

Figure R. 8 .

 8 Figure R.8.

Figure R. 8 :Figure R. 9 :

 89 Figure R.8 : Evolution de (a) la distance inter-feuillet et (b) les paramètres de maille a et b des phases O'3, O3 et P3-NaxMn1-yFeyO2 au cours de la désintercalation électrochimique. (c) Courbe galvanostatique correspondante.

Figure R. 10 :

 10 Figure R.10 :Représentation schématique de l'évolution du diagramme de phase de NaxMn1-3Fe2/3O2 au cours de la désintercalation électrochimique déduit de l'expérience in situ.

  b) Fe K-edge Energy (eV) Absorption (a.u.) -244-Spectroscopie Mössbauer du 57 Fe in et ex situ Le spectre Mössbauer du 57 Fe de la phase initiale O3-Na0.77Mn1/3Fe2/3O2 est donné Figure R.13a. Le spectre montre un doublet quadripolaire qui peut être décrit par un profil de type Lorentzien. L'affinement nécessite deux sites Mössbauer (Tableau R.2). Les déplacements isomériques correspondent à des ions Fe 3+ à haut spin dans des environnements octaédriques. Ces sites, appelés Fe 3+ (A) et Fe 3+ (B), sont représentés respectivement par des lignes bleues et vertes sur la Figure R.13a, respectivement. L'important éclatement quadripolaire associé au site Fe 3+ (A) (ΔA = 0.88 mm.s -1 ) indique que l'environnement de ces octaèdre FeO6 de ce site est davantage soumis au désordre environnant que pour le site Fe 3+ (B) (ΔB = 0.58 mm.s -1 ). Les populations associées montrent qu'une nette majorité du fer est localisé dans le site Fe 3+ (B) (75 %). Dans la littérature, Yabuuchi et al. ont également utilisé deux sites Fe 3+pour décrire le spectre de P2-Na2/3Mn1/2Fe1/2O2[26].

Figure R. 12 .Tableau R. 2 :

 122 Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée.

Tableau R. 3 :

 3 Formules développées et paramètres Mössbauer correspondant aux affinements des spectres présentés Figure R.13. Les écartstypes sur les valeurs des déplacements isomériques sont égaux à 0.002 mm.s -1 . La population du site Fe (3+z)+ est redistribuée entre les sites Fe 3+ et Fe 4+ selon la formule : P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).-248-R.1.d. Comparaison des différents systèmes NaxMn1-yFeyO2Comparaison des diagrammes de phaseLes diagrammes de phase des différents systèmes P2 et O3-NaxMn1-yFeyO2 déduits par diffraction des rayons-X menée in situ pendant la charge complète de batteries Na sont donnés Figure R.14.

Figure R. 14 :

 14 Figure R.14 : Domaines d'observation des phases O'3, O3, P3 et « X » (systèmes de type O3) et des phases P'2, P2 et « Z » (systèmes de type P2) en fonction du taux de Na. Tous les systèmes (P2 ou O3) montrent un comportement similaire (i) une phase distordue (P'2 ou O'3) pour les états les plus intercalés et (ii) une importante perte de cristallinité pour les états les plus désintercalés (E ≈ 4.3 V).

entre 1 ,Figure R. 18 :

 118 Figure R.18 : (a) courbe galvanostatique et (b) évolution de la capacité en décharge pour une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Régime : C/50.La première décharge confirme l'état d'intercalation maximal du matériau de départ. Le profil de charge consiste en une succession de plateaux et de sauts de potentiels entre les compositions x = 1 ; 2/3 ; 1/2 et 2/5. Un comportement de type « solution solide » est observé entre x = 2/5 et x = 1/3. Les composés définis observés pour x = 2/3 ; 1/2 ; 2/5 et 1/3 correspondent à ceux observés pour x' = 0,91 ; 0,84 ; 0,81 et 0,79 dans l'étude de Braconnier et al.[38]. Cette différence entre les taux de sodium vient probablement des meilleurs moyens matériels mis à notre disposition pour cette étude. Lors de la seconde décharge une réversibilité partielle est observée. Deux différences majeures affectent la courbe de deuxième décharge :(i) le saut de potentiel observé à x = 2/5 en charge est remplacé par deux sauts de potentiel successifs en décharge et (ii) l'état d'intercalation maximal est atteint pour x = 0,83. Ce deuxième phénomène avait déjà été observé par Vassiliaras et al.[34].

Figure R. 19 :

 19 Figure R.19 :Courbe de cyclage en mode GITT enregistrée pour une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Régime : C/50 (pas de 0.005 Na + / unité formulaire), temps de relaxation : 30 minutes.

Figue R. 21 :Figure R. 22 : 3 -

 21223 Figue R.21 : (a,b) Zooms dans le domaine 15,5 -17,3° (2θ Cu kα1) des diffractogrammes présentés Figure R.20.

Figure R. 23 :

 23 Figure R.23 : Zoom dans le domaine 15,4 -16,6° (2θ Cu kα1) des diffractogrammes dans le domaine 2/5 ≤ x ≤ 1/2. Lors de la désintercalation, une augmentation continue de la distance inter-feuillet est normalement attendue. Cependant, la distance inter-feuillet des phases P''3-Na1/2NiO et O''3-Na2/5NiO2 est similaire (≈ 5.59 Å). Cette similitude est expliquée par l'évolution de la géométrie des sites NaO6, de prismatique à octaédrique, plus compacte. Entre les compositions x = 1/2 et x = 2/5, un comportement complexe est observé : d'abord la distance inter-feuillets augmente des diffractogrammes #18 (x = 1/2) à #20. Elle reste ensuite constante pour les diffractogrammes #20 à #21 et décroit des diffractogrammes #21 à #22. Cela peut être expliqué par la compétition entre deux effets opposés :

Figure R. 25 :

 25 Figure R.25 : Affinements de type LeBail des profils pour les phases (a) P'3-Na2/3NiO2, (b) P''3-Na1/2NiO2 et (c) O'3-Na2/5NiO2. Le symbole ¤ correspond aux pics de diffractions de NiO. Les indices de Miller noirs et bleus correspondent respectivement aux indexations de la sous-maille et de la sur-maille.

Figure I. 1 :Figure I. 2 :

 12 Figure I.1: Representations of (a) the α-NaFeO2 structure in the NaCl rock salt-type structure and (b) the distortion of the cell due to the Na + / Fe 3+ altering.Figure I.2: Representation of the α-NaFeO2 structure in the hexagonal symmetry (the unit cell is shown by black lines) highlighting the altering of the FeO6 and NaO6 octahedra layers along the chex axis.Figure I.3: Representation of the O3, P3 and P3 structure types. The Na + environment of the different structure types is also represented. Table I.1: Usual space groups and atomic positions for the O3, P3 and P2 structure types.Figure I.4: Representation of the ground electronic states and lift of degeneracy of 3d orbitals for the (a) HS 3d 4 and (c) LS 3d 7 configuration states. A schematic representation of the corresponding MO6 octahedra is also given (b).Figure I.5: Projections of the distorted structures in the (amon.,cmon.) and (amon.,bmon.) planes (O'3, P'3) or in the (borth.,corth.) and (aorth.,borth.) ones (P'2). TableI.2: Usual space groups and atomic positions for the P'2, P'3 and O'3 distorted structure types. TableI.3: Relations between the hexagonal cell parameters and the orthorhombic (P2 / P'2 structures) or monoclinic (O3 / O'3 and P3 / P'3) ones for a non-distorted example. Figure I.6: Representation of the relations between the hexagonal cell and the two possible monoclinic ones. For more clarity the monoclinic cells have been shifted and only the transition metal atoms are represented. Figure I.7: Representation of the interslab distance (left) and in plane M-M distances (right) into the orthorhombic and monoclinic structures. Table I.4: Relations between the cell parameters of the different structures and the interslab and in plane M-M distances. Table I.5: Cell parameters, amon./bmon. ratios and M-O distances in the O'3-NaNiO2 and O'3-NaMnO2 materials. Figure I.8: Representation of a Na battery in (a) its initial state and during (b) the charge and (c) the discharge of the cell.Figure I.9: Schematic representation of the possible behaviors observed in a galvanostatic cycling.Table I.6: Electrochemical properties of different NaxMO2 materials. All voltages ranges are expressed versus the Na + /Na redox couple. Table I.7a: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple. Table I.7b: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple.

Figure I. 3 :

 3 Figure I.1: Representations of (a) the α-NaFeO2 structure in the NaCl rock salt-type structure and (b) the distortion of the cell due to the Na + / Fe 3+ altering.Figure I.2: Representation of the α-NaFeO2 structure in the hexagonal symmetry (the unit cell is shown by black lines) highlighting the altering of the FeO6 and NaO6 octahedra layers along the chex axis.Figure I.3: Representation of the O3, P3 and P3 structure types. The Na + environment of the different structure types is also represented. Table I.1: Usual space groups and atomic positions for the O3, P3 and P2 structure types.Figure I.4: Representation of the ground electronic states and lift of degeneracy of 3d orbitals for the (a) HS 3d 4 and (c) LS 3d 7 configuration states. A schematic representation of the corresponding MO6 octahedra is also given (b).Figure I.5: Projections of the distorted structures in the (amon.,cmon.) and (amon.,bmon.) planes (O'3, P'3) or in the (borth.,corth.) and (aorth.,borth.) ones (P'2). TableI.2: Usual space groups and atomic positions for the P'2, P'3 and O'3 distorted structure types. TableI.3: Relations between the hexagonal cell parameters and the orthorhombic (P2 / P'2 structures) or monoclinic (O3 / O'3 and P3 / P'3) ones for a non-distorted example. Figure I.6: Representation of the relations between the hexagonal cell and the two possible monoclinic ones. For more clarity the monoclinic cells have been shifted and only the transition metal atoms are represented. Figure I.7: Representation of the interslab distance (left) and in plane M-M distances (right) into the orthorhombic and monoclinic structures. Table I.4: Relations between the cell parameters of the different structures and the interslab and in plane M-M distances. Table I.5: Cell parameters, amon./bmon. ratios and M-O distances in the O'3-NaNiO2 and O'3-NaMnO2 materials. Figure I.8: Representation of a Na battery in (a) its initial state and during (b) the charge and (c) the discharge of the cell.Figure I.9: Schematic representation of the possible behaviors observed in a galvanostatic cycling.Table I.6: Electrochemical properties of different NaxMO2 materials. All voltages ranges are expressed versus the Na + /Na redox couple. Table I.7a: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple. Table I.7b: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple.

Figure I. 6 :Figure I. 7 :. 4 :. 5 :Figure I. 8 :Figure I. 9 :

 674589 Figure I.1: Representations of (a) the α-NaFeO2 structure in the NaCl rock salt-type structure and (b) the distortion of the cell due to the Na + / Fe 3+ altering.Figure I.2: Representation of the α-NaFeO2 structure in the hexagonal symmetry (the unit cell is shown by black lines) highlighting the altering of the FeO6 and NaO6 octahedra layers along the chex axis.Figure I.3: Representation of the O3, P3 and P3 structure types. The Na + environment of the different structure types is also represented. Table I.1: Usual space groups and atomic positions for the O3, P3 and P2 structure types.Figure I.4: Representation of the ground electronic states and lift of degeneracy of 3d orbitals for the (a) HS 3d 4 and (c) LS 3d 7 configuration states. A schematic representation of the corresponding MO6 octahedra is also given (b).Figure I.5: Projections of the distorted structures in the (amon.,cmon.) and (amon.,bmon.) planes (O'3, P'3) or in the (borth.,corth.) and (aorth.,borth.) ones (P'2). TableI.2: Usual space groups and atomic positions for the P'2, P'3 and O'3 distorted structure types. TableI.3: Relations between the hexagonal cell parameters and the orthorhombic (P2 / P'2 structures) or monoclinic (O3 / O'3 and P3 / P'3) ones for a non-distorted example. Figure I.6: Representation of the relations between the hexagonal cell and the two possible monoclinic ones. For more clarity the monoclinic cells have been shifted and only the transition metal atoms are represented. Figure I.7: Representation of the interslab distance (left) and in plane M-M distances (right) into the orthorhombic and monoclinic structures. Table I.4: Relations between the cell parameters of the different structures and the interslab and in plane M-M distances. Table I.5: Cell parameters, amon./bmon. ratios and M-O distances in the O'3-NaNiO2 and O'3-NaMnO2 materials. Figure I.8: Representation of a Na battery in (a) its initial state and during (b) the charge and (c) the discharge of the cell.Figure I.9: Schematic representation of the possible behaviors observed in a galvanostatic cycling.Table I.6: Electrochemical properties of different NaxMO2 materials. All voltages ranges are expressed versus the Na + /Na redox couple. Table I.7a: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple. Table I.7b: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple.

Figure II. 1 :Figure II. 2 :Figure II. 3 :Figure II. 4 :Figure II. 5 :

 12345 Figure II.1: (a) Schematic representation of the Swagelok™-type cell and (b) picture of a Swagelok™-type battery. Figure II.2: (a) Schematic description of a coin cell, (b) picture of the corresponding parts and (c) top and bottom view of a sealed coin cell.Figure II.3: Schematic representation of the GITT mode: evolution of the voltage of a Na battery as a function of time.Figure II.4: Comparison between the GITT and the galvanostatic curves for two batteries involving the same positive electrode material.Figure II.5: Schematic representation of the potentiostatic synthesis route. Table II.1: Experimental conditions concerning the XRPD and Synchrotron XRPD experiments carried out in this work. Figure II.6: Cells used for (left) Panalytical and (right) Bruker diffractometers. Figure II.7: Rezoning (a) emission and (b) absorption of a γ photon. Figure II.8: Graphical representation of the isomer shift δ and the quadrupole splitting Δ for a doublet observed in a Mössbauer spectrum. Figure II.9: Quadrupole splitting diagram of the Ie = 3/2 level of an excited 57 Fe nucleus. Figure II.10: (a) Schematic representation and (b) photography of the Mössbauer in situ cell.Figure II.11: Transmission of an X-ray beam through a slab of thickness t.Figure II.12: Schematic representation of the measurement setup line of a XAS experiment. Figure II.13: Variation of the absorption through the absorption coefficient as a function of the incident photon energy.Figure II.14: Example of a XAS spectrum and its division into the XANES and EXAFS subparts.

Figure II. 6 :Figure II. 7 :Figure II. 8 : 9 :Figure II. 13 :Figure II. 14 :Figure A-I. 1 :

 678913141 Figure II.1: (a) Schematic representation of the Swagelok™-type cell and (b) picture of a Swagelok™-type battery. Figure II.2: (a) Schematic description of a coin cell, (b) picture of the corresponding parts and (c) top and bottom view of a sealed coin cell.Figure II.3: Schematic representation of the GITT mode: evolution of the voltage of a Na battery as a function of time.Figure II.4: Comparison between the GITT and the galvanostatic curves for two batteries involving the same positive electrode material.Figure II.5: Schematic representation of the potentiostatic synthesis route. Table II.1: Experimental conditions concerning the XRPD and Synchrotron XRPD experiments carried out in this work. Figure II.6: Cells used for (left) Panalytical and (right) Bruker diffractometers. Figure II.7: Rezoning (a) emission and (b) absorption of a γ photon. Figure II.8: Graphical representation of the isomer shift δ and the quadrupole splitting Δ for a doublet observed in a Mössbauer spectrum. Figure II.9: Quadrupole splitting diagram of the Ie = 3/2 level of an excited 57 Fe nucleus. Figure II.10: (a) Schematic representation and (b) photography of the Mössbauer in situ cell.Figure II.11: Transmission of an X-ray beam through a slab of thickness t.Figure II.12: Schematic representation of the measurement setup line of a XAS experiment. Figure II.13: Variation of the absorption through the absorption coefficient as a function of the incident photon energy.Figure II.14: Example of a XAS spectrum and its division into the XANES and EXAFS subparts.

Figure A-I. 3 : 4 :

 34 Figure A-I.1: (a) photography and (b) Scanning Electron Microscopy micrograph of the product of the selfcombustion synthesis of a NaxMn1-yFeyO2 material after grinding.Figure A-I.3: Schematic representation of the heat treatment step of the NaxMn1-yFeyO2 materials. Figure A-I.4: Phase diagrams as a function of the sodium content for the NaxMn1/3Fe2/3O2, NaxMn1/2Fe1/2O2 and NaxMn1/3Fe2/3O2 systems.Figure A-I.5: Observed and calculated XRPD patterns for (a) the P2-Na0.77Mn2/3Fe1/3O2, (b) the P2-Na0.67Mn1/2Fe1/2O2, (c) the (O3+O'3)Na0.82Mn1/2Fe1/2O2 and (d) the O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.1: Cell parameters and Interslab distances of the P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3)Na0.82Mn1/2Fe1/2O2 and O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.2: ICP-AES results for the pristine materials synthesized by self-combustion synthesis.Figure A-I.6: Scanning Electron Microscopy micrographs for (a) the P2-Na0.67Mn1/2Fe1/2O2 and (b) the O3-Na0.82Mn1/3Fe2/3O2 phases. Figure A-I.7: Galvanostatic cycling curves involving the O3-Na0.77Mn1/3Fe2/3O2 material at the positive electrode recorded between 1.5 and 3.8 V at C/50: (a) without any additive, (b) with the VC electrolyte additive and (c) with the FEC electrolyte additive. The associated discharge capacities are also represented (d).Figure A-I.8: Galvanostatic cycling curves of the Na/ NaPF6 in PC (1 M) + 2 wt% FEC /NaxMn1-yFeyO2 cells obtained at a C/50 rate starting by a discharge between 1.5 and 3.8 V. (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 and (d) O3-Na0.77Mn1/3Fe2/3O2. A magnification of each curve around the starting point is shown in the insets. Table A-I.3: Values of the voltage plateaus associated to the first discharge and first charge for the different NaxMn1-yFeyO2 materials.Figure A-I.9: Discharge capacities corresponding to the Na//NaxMn1-yFeyO2 cells cycled between 1.5 and 3.8 V and assembled from the P2-Na0.66Mn2/3Fe1/3O3 (black), P2-Na0.62Mn1/2Fe1/2O2 (blue), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (red) and O3-Na0.77Mn1/3Fe2/3O2 (green) materials.

Figure A-I. 5 : 1 :

 51 Figure A-I.1: (a) photography and (b) Scanning Electron Microscopy micrograph of the product of the selfcombustion synthesis of a NaxMn1-yFeyO2 material after grinding.Figure A-I.3: Schematic representation of the heat treatment step of the NaxMn1-yFeyO2 materials. Figure A-I.4: Phase diagrams as a function of the sodium content for the NaxMn1/3Fe2/3O2, NaxMn1/2Fe1/2O2 and NaxMn1/3Fe2/3O2 systems.Figure A-I.5: Observed and calculated XRPD patterns for (a) the P2-Na0.77Mn2/3Fe1/3O2, (b) the P2-Na0.67Mn1/2Fe1/2O2, (c) the (O3+O'3)Na0.82Mn1/2Fe1/2O2 and (d) the O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.1: Cell parameters and Interslab distances of the P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3)Na0.82Mn1/2Fe1/2O2 and O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.2: ICP-AES results for the pristine materials synthesized by self-combustion synthesis.Figure A-I.6: Scanning Electron Microscopy micrographs for (a) the P2-Na0.67Mn1/2Fe1/2O2 and (b) the O3-Na0.82Mn1/3Fe2/3O2 phases. Figure A-I.7: Galvanostatic cycling curves involving the O3-Na0.77Mn1/3Fe2/3O2 material at the positive electrode recorded between 1.5 and 3.8 V at C/50: (a) without any additive, (b) with the VC electrolyte additive and (c) with the FEC electrolyte additive. The associated discharge capacities are also represented (d).Figure A-I.8: Galvanostatic cycling curves of the Na/ NaPF6 in PC (1 M) + 2 wt% FEC /NaxMn1-yFeyO2 cells obtained at a C/50 rate starting by a discharge between 1.5 and 3.8 V. (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 and (d) O3-Na0.77Mn1/3Fe2/3O2. A magnification of each curve around the starting point is shown in the insets. Table A-I.3: Values of the voltage plateaus associated to the first discharge and first charge for the different NaxMn1-yFeyO2 materials.Figure A-I.9: Discharge capacities corresponding to the Na//NaxMn1-yFeyO2 cells cycled between 1.5 and 3.8 V and assembled from the P2-Na0.66Mn2/3Fe1/3O3 (black), P2-Na0.62Mn1/2Fe1/2O2 (blue), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (red) and O3-Na0.77Mn1/3Fe2/3O2 (green) materials.

Figure A-I. 6 : 7 :

 67 Figure A-I.1: (a) photography and (b) Scanning Electron Microscopy micrograph of the product of the selfcombustion synthesis of a NaxMn1-yFeyO2 material after grinding.Figure A-I.3: Schematic representation of the heat treatment step of the NaxMn1-yFeyO2 materials. Figure A-I.4: Phase diagrams as a function of the sodium content for the NaxMn1/3Fe2/3O2, NaxMn1/2Fe1/2O2 and NaxMn1/3Fe2/3O2 systems.Figure A-I.5: Observed and calculated XRPD patterns for (a) the P2-Na0.77Mn2/3Fe1/3O2, (b) the P2-Na0.67Mn1/2Fe1/2O2, (c) the (O3+O'3)Na0.82Mn1/2Fe1/2O2 and (d) the O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.1: Cell parameters and Interslab distances of the P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3)Na0.82Mn1/2Fe1/2O2 and O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.2: ICP-AES results for the pristine materials synthesized by self-combustion synthesis.Figure A-I.6: Scanning Electron Microscopy micrographs for (a) the P2-Na0.67Mn1/2Fe1/2O2 and (b) the O3-Na0.82Mn1/3Fe2/3O2 phases. Figure A-I.7: Galvanostatic cycling curves involving the O3-Na0.77Mn1/3Fe2/3O2 material at the positive electrode recorded between 1.5 and 3.8 V at C/50: (a) without any additive, (b) with the VC electrolyte additive and (c) with the FEC electrolyte additive. The associated discharge capacities are also represented (d).Figure A-I.8: Galvanostatic cycling curves of the Na/ NaPF6 in PC (1 M) + 2 wt% FEC /NaxMn1-yFeyO2 cells obtained at a C/50 rate starting by a discharge between 1.5 and 3.8 V. (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 and (d) O3-Na0.77Mn1/3Fe2/3O2. A magnification of each curve around the starting point is shown in the insets. Table A-I.3: Values of the voltage plateaus associated to the first discharge and first charge for the different NaxMn1-yFeyO2 materials.Figure A-I.9: Discharge capacities corresponding to the Na//NaxMn1-yFeyO2 cells cycled between 1.5 and 3.8 V and assembled from the P2-Na0.66Mn2/3Fe1/3O3 (black), P2-Na0.62Mn1/2Fe1/2O2 (blue), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (red) and O3-Na0.77Mn1/3Fe2/3O2 (green) materials.

Figure A-I. 8 : 3 :

 83 Figure A-I.1: (a) photography and (b) Scanning Electron Microscopy micrograph of the product of the selfcombustion synthesis of a NaxMn1-yFeyO2 material after grinding.Figure A-I.3: Schematic representation of the heat treatment step of the NaxMn1-yFeyO2 materials. Figure A-I.4: Phase diagrams as a function of the sodium content for the NaxMn1/3Fe2/3O2, NaxMn1/2Fe1/2O2 and NaxMn1/3Fe2/3O2 systems.Figure A-I.5: Observed and calculated XRPD patterns for (a) the P2-Na0.77Mn2/3Fe1/3O2, (b) the P2-Na0.67Mn1/2Fe1/2O2, (c) the (O3+O'3)Na0.82Mn1/2Fe1/2O2 and (d) the O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.1: Cell parameters and Interslab distances of the P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3)Na0.82Mn1/2Fe1/2O2 and O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.2: ICP-AES results for the pristine materials synthesized by self-combustion synthesis.Figure A-I.6: Scanning Electron Microscopy micrographs for (a) the P2-Na0.67Mn1/2Fe1/2O2 and (b) the O3-Na0.82Mn1/3Fe2/3O2 phases. Figure A-I.7: Galvanostatic cycling curves involving the O3-Na0.77Mn1/3Fe2/3O2 material at the positive electrode recorded between 1.5 and 3.8 V at C/50: (a) without any additive, (b) with the VC electrolyte additive and (c) with the FEC electrolyte additive. The associated discharge capacities are also represented (d).Figure A-I.8: Galvanostatic cycling curves of the Na/ NaPF6 in PC (1 M) + 2 wt% FEC /NaxMn1-yFeyO2 cells obtained at a C/50 rate starting by a discharge between 1.5 and 3.8 V. (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 and (d) O3-Na0.77Mn1/3Fe2/3O2. A magnification of each curve around the starting point is shown in the insets. Table A-I.3: Values of the voltage plateaus associated to the first discharge and first charge for the different NaxMn1-yFeyO2 materials.Figure A-I.9: Discharge capacities corresponding to the Na//NaxMn1-yFeyO2 cells cycled between 1.5 and 3.8 V and assembled from the P2-Na0.66Mn2/3Fe1/3O3 (black), P2-Na0.62Mn1/2Fe1/2O2 (blue), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (red) and O3-Na0.77Mn1/3Fe2/3O2 (green) materials.

Figure A-I. 9 :Figure A-II. 1 : 1 :

 911 Figure A-I.1: (a) photography and (b) Scanning Electron Microscopy micrograph of the product of the selfcombustion synthesis of a NaxMn1-yFeyO2 material after grinding.Figure A-I.3: Schematic representation of the heat treatment step of the NaxMn1-yFeyO2 materials. Figure A-I.4: Phase diagrams as a function of the sodium content for the NaxMn1/3Fe2/3O2, NaxMn1/2Fe1/2O2 and NaxMn1/3Fe2/3O2 systems.Figure A-I.5: Observed and calculated XRPD patterns for (a) the P2-Na0.77Mn2/3Fe1/3O2, (b) the P2-Na0.67Mn1/2Fe1/2O2, (c) the (O3+O'3)Na0.82Mn1/2Fe1/2O2 and (d) the O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.1: Cell parameters and Interslab distances of the P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3)Na0.82Mn1/2Fe1/2O2 and O3-Na0.82Mn1/3Fe2/3O2 phases. Table A-I.2: ICP-AES results for the pristine materials synthesized by self-combustion synthesis.Figure A-I.6: Scanning Electron Microscopy micrographs for (a) the P2-Na0.67Mn1/2Fe1/2O2 and (b) the O3-Na0.82Mn1/3Fe2/3O2 phases. Figure A-I.7: Galvanostatic cycling curves involving the O3-Na0.77Mn1/3Fe2/3O2 material at the positive electrode recorded between 1.5 and 3.8 V at C/50: (a) without any additive, (b) with the VC electrolyte additive and (c) with the FEC electrolyte additive. The associated discharge capacities are also represented (d).Figure A-I.8: Galvanostatic cycling curves of the Na/ NaPF6 in PC (1 M) + 2 wt% FEC /NaxMn1-yFeyO2 cells obtained at a C/50 rate starting by a discharge between 1.5 and 3.8 V. (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 and (d) O3-Na0.77Mn1/3Fe2/3O2. A magnification of each curve around the starting point is shown in the insets. Table A-I.3: Values of the voltage plateaus associated to the first discharge and first charge for the different NaxMn1-yFeyO2 materials.Figure A-I.9: Discharge capacities corresponding to the Na//NaxMn1-yFeyO2 cells cycled between 1.5 and 3.8 V and assembled from the P2-Na0.66Mn2/3Fe1/3O3 (black), P2-Na0.62Mn1/2Fe1/2O2 (blue), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (red) and O3-Na0.77Mn1/3Fe2/3O2 (green) materials.

Figure A-II. 2 : 2 :

 22 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 3 :

 3 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 4 :

 4 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 5 :

 5 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 7 :

 7 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 8 :

 8 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 9 :

 9 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 10 :

 10 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 11 :

 11 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 12 : 3 :

 123 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 14 : 4 :

 144 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 15 : 5 :

 155 Figure A-II.1: Observed and calculated (Rietveld method) synchrotron XRPD pattern for the O3-Na0.77Mn1/3Fe2/3O2 starting phase. Table A-II.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the O3-Na0.77Mn1/3Fe2/3O2 starting phase.Figure A-II.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the O3-Na0.77Mn1/3Fe2/3O2 pristine material. Table A-II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.Figure A-II.3: Galvanostatic cycling curves associated to the NaxMn1/3Fe2/3O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state.Figure A-II.4: SEM micrographs of (a,b) an un-cycled electrode involving the O3-Na0.77Mn1/3Fe2/3O2 material and similar electrodes cycled 50 times (c,d) between 1.5 and 3.8 V, (e,f) between 1.5 and 4.0 V and (g,h) between 1.5 and 4.3 V.Figure A-II.5: GITT cycling of the NaxMn1/3fe2/3O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-II.6: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve.Figure A-II.7: Inverse representation of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve.Figure A-II.8: (left) XRPD patterns recorded in situ during the relaxation of a NaxMn1/3Fe2/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (right) the corresponding galvanostatic GITT curve.Figure A-II.9: Evolution of the (a) interslab distance and (b) a and b cell parameters of the O'3, O3 and P3-NaxMn1/3Fe2/3O2 phases upon sodium deintercalation. The galvanostatic curve is shown as a guide (c).Figure A-II.10: Magnifications in the 0.3 ≤ x ≤ 0.7 region of the XRPD patterns recorded during the operando in situ XRPD experiment carried out on the NaxMn1/3Fe2/3O2. The blue lines highlight the limitations of the solid solutions and / or biphasic domains.Figure A-II.11: Schematic representation of the NaxMn1/3Fe2/3O2 phase diagram upon Na deintercalation deduced from the operando in situ XRPD experiment. In the 0.16 < x < 0.62 range, several systems (related to O3 and P3) are simultaneously observed.Figure A-II.12: XRPD patterns recorded in situ during a potentiostatic step (1.5 V) after a) the first and b) the second discharges of the operando in situ experiment carried out on the NaxMn1/3Fe2/3O2 system.Figure A-II.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O'3-Na0.96Mn1/3Fe2/3O2 phase. Table A-II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.Figure A-II.14: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the O3-Na2/3Mn1/3Fe2/3O2 phase. Table A-II.4: Structural parameters and reliability factors calculated from the refinement of the structure of the O3 phase from the synchrotron XRPD pattern.Figure A-II.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P3-Na0.57Mn1/3Fe2/3O2 phase. Table A-II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

Figure A-II. 16 :

 16 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 17 :

 17 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 18 :

 18 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 19 :

 19 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 20 :

 20 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 21 :

 21 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 22 :

 22 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 23 :

 23 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 24 : 6 :

 246 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 25 :

 25 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 26 :

 26 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 27 : 7 :Figure A-II. 28 : 8 :

 277288 Figure A-II.16: Comparison of the distances in the MO6 and NaO6 polyedra in a) O'3-Na0.96Mn1/3Fe2/3O2, b) O3-Na2/3Mn1/3Fe2/3O2 and c) P3-Na0.61Mn1/3Fe2/3O2. The MO2 slab thicknesses are also indicated. For the O3 and P3 type phases, only a part of the stacking sequence is shown for clarity purposes.Figure A-II.17: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/50. (d) Associated discharge capacities. The capacities of the first cycles are not shown on (d) as they correspond to the partially intercalated state of the material.Figure A-II.18: GITT cyclings with steps of 0.01 Na per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the (a) NaxMn1/2Fe1/2O2 and (b) NaxMn1/3Fe2/3O2 compositions.Figure A-II.19: (a) XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.20: Inverse representation of the operando in situ experiment carried out on the NaxMn1/2Fe1/2O2 system: (a) XRPD patterns and (b) corresponding galvanostatic curve. Blue Miller indexes: O3 and P3 phases. The red XRPD patterns correspond to the limitations of the different structural domains.Figure A-II.21: Evolution of the (a) interslab distances and (b) cell parameters of the different phases observed in the NaxMn1/2Fe1/2O2 system during the operando in situ XRPD study. The galvanostatic curve is shown as a guide on (c).Figure A-II.22: XRPD patterns recorded in situ (operando mode) during the charge of an NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na cell: highlighting of the intermediate phases (green, pink and blue arrow).Figure A-II.23: Comparison of the XRPD patterns of the NaxMn1/2Fe1/2O2 system recorded under constant voltage at 1.5 V: (a) at the beginning of the operando in situ XRPD experiment and (b) after cycling to 4.3 V and discharge back to 1.5 V.Figure A-II.24: Observed and calculated (Rietveld Method) synchrotron XRPD patterns of the O'3-Na0.95Mn1/2Fe1/2O2 phase. Table A-II.6: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3-Na0.95Mn1/2Fe1/2O2 phase from the synchrotron XRPD pattern.Figure A-II.25: Open current voltage charging curves extracted from the GITT cycling cones for (red) NaxMn1/2Fe1/2O2 and (blue) NaxMn1/3Fe2/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.Figure A-II.26: Operando In situ X-ray Absorption Near Edge Spectroscopy (XANES) spectra corresponding to the Mn and Fe K-edges and recorded during the charge of the (a,b) Na//NaxMn1/3Fe2/3O2 and(c,d) Na//NaxMn1/2Fe1/2O2 cells. The Mn references for Mn 3+ (Mn2O3) and Mn 4+ (Li2MnO3) are given in (e). The Fe references for Fe 2+ (FeO), Fe 3+ (Fe2O3, NaFeO2) and Fe 3.45+ (Na0.55FeO2) are given in (f). Figure A-II.27: 57 Fe Mössbauer spectra (a) of the pristine material and (b) recorded in situ during the charge of a NaxMn1/3Fe2/3O2 //Na battery. Table A-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine material.Figure A-II.28: Superposition of different Mössbauer spectra in the NaxMn1/3Fe2/3O2 system: (a) x = 0.96 (black line), x = 0.86 (red line) and x = 0.67 (blue line) compositions and (b) x = 0.96 (black line), x = 0.58 (red line) and x = 0.38 (blue line) compositions. Table A-II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27bfor the NaxMn1/3Fe2/3O2 system. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 29 :

 29 Figure A-II.29: 57 Fe Mössbauer spectra recorded ex situ for the NaxMn1/2Fe1/2O2 system at the (a) x = 0.95, (b) x = 0.67, (c) x = 0.55, (d) x = 0.44 and (e) x = 0.22 compositions. Black circles: experimental and red lines: calculated. The different Mössbauer sites deduced from the Lorentzian fittings are represented by the blue, pink and green lines.Figure A-II.30: Comparison of the Mössbauer spectra recorded for the NaxMn1/2Fe1/2O2 system. Black dots: experimental and red line: calculated. Table A-II.9: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra of the NaxMn1/2Fe1/2O2 system presented in Figure A-II.29.The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-II. 30 : 9 :Figure A-III. 1 : 1 :

 30911 Figure A-II.29: 57 Fe Mössbauer spectra recorded ex situ for the NaxMn1/2Fe1/2O2 system at the (a) x = 0.95, (b) x = 0.67, (c) x = 0.55, (d) x = 0.44 and (e) x = 0.22 compositions. Black circles: experimental and red lines: calculated. The different Mössbauer sites deduced from the Lorentzian fittings are represented by the blue, pink and green lines.Figure A-II.30: Comparison of the Mössbauer spectra recorded for the NaxMn1/2Fe1/2O2 system. Black dots: experimental and red line: calculated. Table A-II.9: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra of the NaxMn1/2Fe1/2O2 system presented in Figure A-II.29.The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

Figure A-III. 2 : 2 :

 22 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 3 :

 3 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 4 : 5 :

 45 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 6 :

 6 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 7 : 8 :

 78 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 9 :

 9 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 10 :

 10 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 11 :

 11 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 12 :

 12 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 13 : 3 :

 133 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 14 :

 14 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 15 : 4 :

 154 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 16 : 5 :

 165 Figure A-III.1: Observed and calculated (Rietveld method) synchrotron XRPD patterns of P2-Na0.62Mn1/2Fe1/2O2. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of P2-Na0.62Mn1/2Fe1/2O2.Figure A-III.2: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns of P2-Na0.62Mn1/2Fe1/2O2. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions.Table A-III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.Figure A-III.3: Galvanostatic cycling curves associated to the NaxMn1/2Fe1/2O2 system and recorded (a,b) between 1.5 and 3.8 V, (c,d) between 1.5 and 4.0 V) and (e,f) between 1.5 and 4.3 V at C/20.Figure A-III.4: Discharge capacities associated to the galvanostatic curves of the NaxMn1/2Fe1/2O2 system recorded in the different voltage ranges (Figure A-III.3). Figure A-III.5: Galvanostatic curves recorded at a C/20 rate between 1.5 -4.3 V (in red) and then between 1.5 -4.0 V (in blue) for the NaxMn1/2Fe1/2O2 system. The insert represents the evolution of the associated discharge capacities.Figure A-III.6: SEM micrographs of (a, b) an un-cycled electrode involving the P2-Na0.62Mn1/2Fe1/2O2 material and similar electrodes cycled 3 times in the (c, d) 2.0 -4.0 V range and in the (e, f) 2.0 -4.3 V one.Figure A-III.7: GITT cycling of the NaxMn1/2Fe1/2O2 system recorded with steps of ≈0.01 Na per formula unit. Relaxation condition: ΔV < 4 mV.h -1 . Figure A-III.8: Evolution of the discharge capacity of the NaxMn1/2Fe1/2O2 system for several rate values.Figure A-III.9: (a) XRPD patterns recorded in situ (operando mode) during the charge of a NaxMn1/2Fe1/2O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.10: Inverse representation of Figure A-III.9: (a) XRPD patterns and (b) corresponding galvanostatic curve. The red XRPD patterns correspond to the limits of the different structural domains.Figure A-III.11: Evolution of (a) the interslab distance and (b) the a and b cell parameters (P'2 and P2 phases) or M-M distance ("Z" phase) of the NaxMn1/2Fe1/2O2 phases upon sodium deintercalation. The galvanostatic curve versus x is shown as a guide in (c).Figure A-III.12: Comparison of the XRPD patterns of P'2 NaxMn1/2Fe1/2O2 phases recorded after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.Figure A-III.13: Observed and calculated (Rietveld method) synchrotron XRPD patterns of the P'2-Na≈1Mn1/2Fe1/2O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the graphite diffraction lines which were excluded for the refinement. Table A-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.14: Representation of the MO6 and NaO6 polyhedra in the P'2-Na≈1Mn1/2Fe1/2O2 phase.Figure A-III.15: Observed and calculated (Rietveld method) synchrotron XRPD patterns for the P2-Na0.66Mn2/3Fe1/3O2 pristine material. Red dots: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. Table A-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.Figure A-III.16: Observed and calculated (Rietveld method) (a) XRPD and (b) neutron powder diffraction patterns for the P2-Na0.662Mn2/3Fe1/3O2 pristine material. Red crosses: experimental, black line: calculated,

Figure A-III. 17 :

 17 Galvanostatic cycling curves associated to the NaxMn2/3Fe1/3O2 system and recorded (a) between 1.5 and 3.8 V, (b) between 1.5 and 4.0 V and (c) between 1.5 and 4.3 V at C/20. (d) Associated discharge capacities. The capacities of the first cycle are not shown in(d) as they correspond to the partially intercalated state.

Figure A-III. 18 :Figure A-III. 19 :

 1819 GITT cycling curve recorded with steps of ≈ 0.01 Na + per formula unit and a ΔV < 4 mV.h -1 relaxation condition for the NaxMn2/3Fe1/3O2 system(a). The red arrows indicate slight variation in the slope of the curve. The GITT cycling curve recorded for the NaxMn1/2Fe1/2O2 system is given in (b) as a comparison. Evolution of the discharge capacity of the NaxMn2/3Fe1/3O2 system for several rate values.

Figure A-III. 20 :

 20 (a) XRPD patterns of the NaxMn2/3Fe1/3O2 material recorded in situ (operando mode) during the charge of a NaxMn2/3Fe1/3O2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell along with (b) the corresponding cycling curve. The red XRPD patterns correspond to the limits of the different structural domains.

Figure A-III. 21 :

 21 Inversed representation of the operando in situ XRPD experiment carried out on the NaxMn2/3Fe1/3O2 system: (a) XRPD patterns and (b) corresponding cycling curve. The red XRPD patterns correspond to the limits of the different structural domains.

Figure A-III. 22 :

 22 Evolution of the (a) interslab distance and (b) a and b cell parameters of the different NaxMn2/3Fe1/3O2 phases upon sodium deintercalation. The galvanostatic curve versus x is also shown as a guide in (c).

Figure A-III. 23 :

 23 Comparison of the XRPD patterns recorded for the P'2-NaxMn2/3Fe1/3O2 phases after (a) the first and (b) second discharge at 1.5 V, and maintained at the voltage until a negligible current was observed.

Figure A-III. 24 :

 24 (a) XRPD patterns recorded in situ during the relaxation periods of a NaxMn2/3Fe1/3O2/NaPF6 in PC (1M) + 2 wt% FEC /Na cell along with (b) the corresponding GITT curve. Only the most important reflections are labeled for clarity purposes.

Figure A-III. 25 :

 25 (a) Zoom in the 30 -45 ° region of the XRPD patterns recorded in situ during the relaxation periods of a NaxMn2/3Fe1/3O2/NaPF6 in PC (1M) + 2 wt% FEC /Na cell along with (b) the corresponding GITT curve. Only the most important reflections are labeled for clarity purposes.

Figure A-III. 26 :

 26 Evolution of the (a) interslab distance and (b) a and b cell parameters of the P2 and P'2-NaxMn2/3Fe1/3O2 phases upon sodium intercalation. The GITT E = f(x) curve is also shown as a guide in (c).

Figure A-III. 27 : 6 :

 276 Observed and calculated (Rietveld method) XRPD patterns of the intercalated P'2-Na0.96Mn2/3Fe1/3O2 phase. Red crosses: experimental, black line: calculated, blue line: difference and green bars: Bragg positions. The * symbol indicates the position of the graphite diffraction lines. Table A-III.Structural parameters and reliability factors calculated from the XRPD diagram of the P'2-Na0.96Mn2/3Fe1/3O2 phase.

Figure A-III. 28 :

 28 Open current voltage charging curves extracted from the GITT cycling cones for (blue) NaxMn1/2Fe1/2O2 and (red) NaxMn2/3Fe1/3O2. The dashed lines represent the expected position of the voltage jump associated to the change of redox process during charge if the redox potentials of Fe 4+ /Fe 3+ and Mn 4+ /Mn 3+ are well separated.

Figure A-III. 29 : 7 :

 297 X-ray absorption near edge spectroscopy spectra recorded in situ and corresponding to the (a) Mn and (b) Fe K-edges of a NaxMn1/2Fe1/2O2 electrode. The spectra of the (c) Mn and (d) Fe references compounds are also given. Table A-III.Mössbauer parameters deduced from the Lorentzian and Distribution fits of the Mössbauer spectrum of the P2-Na0.62Mn1/2Fe1/2O2 pristine material.

Figure A-III. 30 :

 30 (a) Lorentzian and (b) distribution fits of the Mössbauer spectrum of the P2-Na0.62Mn1/2Fe1/2O2 pristine material. (c) Distribution profile corresponding to the distribution fit.

Figure A-III. 31 : 8 :

 318 57 Fe Mössbauer spectra of (a) P'2-Na≈1Mn1/2Fe1/2O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) P2-Na0.5Mn1/2Fe1/2O2, (d) P2-Na0.45Mn1/2Fe1/2O2, (e) "Z"-Na0.24Mn1/2Fe1/2O2 and (f) "Z"-Na0.14Mn1/2Fe1/2O2. Black -273-circles: experimental and red line: calculated. Blue, pink, green and brown lines:57 Fe Mössbauer sites (Lorentzian fits only). Table A-III.Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra of the NaxMn1/2Fe1/2O2 system presented in Figure A-III.31. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 .

Figure A-III. 32 : 9 :

 329 Comparison of the Mössbauer spectra recorded in the P2-based NaxMn1/2Fe1/2O2 system. Table A-III.Mössbauer parameters deduced from the Lorentzian and Distribution fits of the Mössbauer spectrum of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.

Figure A-III. 33 :

 33 (a) Lorentzian and (b) distribution fits of the Mössbauer spectrum of the P2-Na0.66Mn2/3Fe1/3O2 pristine material. (c) Distribution profile corresponding to the distribution fit.

Figure A-III. 34 : 10 :Figure A-IV. 1 :

 34101 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).Figure A-IV.4: Evolution of the discharge capacities for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-

Figure A-IV. 2 :

 2 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).Figure A-IV.4: Evolution of the discharge capacities for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-

Figure A-IV. 3 :

 3 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).Figure A-IV.4: Evolution of the discharge capacities for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-

Figure A-IV. 4 :

 4 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).Figure A-IV.4: Evolution of the discharge capacities for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-

Figure A-IV. 5 :

 5 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).Figure A-IV.4: Evolution of the discharge capacities for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-

Figure A-IV. 6 :

 6 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).Figure A-IV.4: Evolution of the discharge capacities for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-

Figure A-IV. 7 :

 7 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).Figure A-IV.4: Evolution of the discharge capacities for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-

Figure A-IV. 8 :

 8 Figure A-IV.1: Evolution of the galvanostatic curves recorded at C/50 for the O3-based NaxMn1/3Fe2/3O2 (red line) and NaxMn1/2Fe1/2O2 (blue line) systems while cycled up to 4.3 V. The dashed grey line corresponds to the E = 4.0 V voltage value.Figure A-IV.2: Evolution of the discharge capacity for the O3-based (a) NaxMn1/3Fe2/3O2 and (b) NaxMn1/2Fe1/2O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.3: Evolution of the galvanostatic curves recorded at C/20 for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems while cycled up to 4.0 V (black lines) and up to 4.3 V (red lines).Figure A-IV.4: Evolution of the discharge capacities for the P2-based (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2 systems in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges.Figure A-IV.5: Evolution of the discharge capacity for different C-rate values for (a) NaxMn1/2Fe1/2O2 and (b) NaxMn2/3Fe1/3O2.Figure A-IV.6: Domains of observation of the O'3, O3, P3 and "X" phases (O3-type materials) and of the P'2, P2 and "Z" phases (P2-type materials).Figure A-IV.7: Comparison of the XRPD patterns recorded in situ during the charge of corresponding Nacells of (a) "X"-Na0.16Mn1/3Fe2/3O2, (b) "X"-Na0.25Mn1/2Fe1/2O2 and (c) "Z"-Na0.25Mn1/2Fe1/2O2. The zero shifts have been corrected for each pattern.Figure A-IV.8: Evolution of the amon./bmon. or borth./aorth. ratios along with the Mn content in the NaxMn1-yFeyO2 materials.Figure A-IV.9: Evolution of the M-O distances in the MO6 octahedra in P'2 and O'3-Na≈1Mn1-yFeyO2 phases.

Figure A-IV. 9 : 1 : 2 :

 912 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 3 :

 3 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 4 : 3 :

 43 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 5 :

 5 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 6 :

 6 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 7 :

 7 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 8 :

 8 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 10 :

 10 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 13 :

 13 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 14 : 4 : 5 :

 1445 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 15 :

 15 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure B-I. 16 :Figure R. 1 :Figure R. 2 :. 1 :Figure R. 3 :Figure R. 4 :Figure R. 5 :

 16121345 Figure B-I.1 and Table B-I.1: Synthesis conditions of the three studied O'3-NaNiO2 materials. Figure B-I.2: XRPD patterns of the three O'3-NaNiO2 samples: (top) large, (middle) medium and (bottom) small grain sizes. ¤ symbol: NiO traces and * symbol: Na≈0.8NiO2. The Miller indexes correspond to the indexation in the monoclinic cell (S.G.: C2/m). Table B-I.2: Cell parameters and amon./bmon. ratios deduced from the LeBail refinement of the profiles of the different O'3-NaNiO2 samples from the XRPD patterns.Figure B-I.3: Scanning Electron Microscopy micrographs of the (a) large grains, (b) medium grains and (c) small grains samples of the O'3-NaNiO2 material.Figure B-I.4: Observed and Calculated (Rietveld method) XRPD patterns of the "large grains" O'3-NaNiO2 sample. Table B-I.3: Structural parameters and reliability factors calculated from the XRPD pattern of the O'3-NaNiO2 sample (large grains).Figure B-I.5: Galvanostatic cycling curves recorded at C/50 between 1.5 and 3.8 V for the (a) large, (b) medium and (c) small grain sized O'3-NaNiO2 materials. The evolution of the discharge capacity as a function of the cycle number is given in (d) for the medium grains sample. The derivative dE/dx curve highlighting the voltage jumps is given in (e) for the "large grains" sample.Figure B-I.6: GITT cycling curve recorded with steps of 0.005 Na per formula unit (C/50) followed by a 30 minutes relaxation time for a NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na battery ("medium grains" sample).Figure B-I.7: GITT cyclings in the 0.5 < x < 1.0 range recorded with steps of ≈ 0.005 Na per formula unit (C/50) followed by a 60 (a) or 30 (b,c) minutes relaxation time for NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na batteries for the (a) large, (b) medium and (c) small grains samples.Figure B-I.8: Evolution of the XRPD patterns recorded in situ during the charge of a NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cell (medium grains sample). The red XRPD patterns highlight the peculiar compositions.Figure B-I.9: (a) Zoom in the 15.5 -17.3° 2θ region of the XRPD patterns recorded during the in situ experiment carried out on the NaxNiO2 system (medium grains sample). (b) Inversed representation. The red XRPD patterns highlight the peculiar compositions.Figure B-I.10: Evolution of the interslab distances of the different NaxNiO2 phases deduced from the position of the (001)mon. diffraction lines and after correction of the "zero shift".Figure B-I.11: Zoom in the 15.4 -16.6° 2θ region of the XRPD patterns recorded around the 2/5 ≤ x ≤ 1/2 range during the in situ experiment.Figure B-I.12: XRPD patterns of the x = 1, 0.8, 2/3, 1/2, 2/5 and 1/3 recorded in situ during the charge of a NaxNiO2/NaPF6 in PC (1M) + 2 wt % FEC/Na battery. The black dashed arrows highlight the appearance of new diffraction peaks.Figure B-I.13: Evolution of the XRPD patterns in the 15.5 -17.5 2θ range recorded in situ during the charge of NaNiO2/NaPF6 in PC (1M) + 2 wt% FEC/Na cells involving the different samples: (a) "large grains", (b)"medium grains" and (c) "small grains".Figure B-I.14: Evolution of the interslab distances deduced from the XRPD patterns recorded in situ during charge of the NaxNiO2/ NaPF6 in PC (1M) + 2 wt% FEC /Na cells with the (a) "large grains", (b) "medium grains" and (c) "small grains" samples. Table B-I.4: Subcell parameters deduced from the LeBail refinement of the profiles of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. Table B-I.5: Supercells and space groups used to describe the P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2 peculiar compositions (and thus including the extra diffraction peaks).Figure B-I.15: LeBail refinement of the XRPD profiles of (a) P'3-Na2/3NiO2, (b) P'3-Na1/2NiO2 and (c) O'3-Na2/5NiO2. The ¤ symbol indicates the NiO diffraction peak.Figure B-I.16: Comparison of the XRPD patterns of the (top) Na≈0.8NiO2 and (bottom) O'3-NaNiO2 phases. The intensity scale is different for both patterns.

Figure R. 6 :Figure R. 7 :Figure R. 8 :Figure R. 9 :Figure R. 10 :Figure R. 11 :. 2 :. 3 :

 6789101123 Figure R.1 : (a) Structures des phases dites « O3 », « P3 » et « P2 », d'après [36]. Les différents environnements autour des ions Na sont également représentés. (b) Structures distordues (« O'3 », « P'3 » et « P'2 ») dérivant des structures « O3 », « P3 » et « P2 ». Figure R.2 : Diffractogrammes de rayons-X expérimentaux et calculés pour (a) P2-Na0.77Mn2/3Fe1/3O2, (b) P2-Na0.67Mn1/2Fe1/2O2, (c) (O3+O'3)Na0.82Mn1/2Fe1/2O2 et (d) O3-Na0.82Mn1/3Fe2/3O2 phases. Croix rouges : observé, ligne noire : calculé, ligne bleue: différence et barres vertes : Bragg. (a, b, d) : affinement de type Rietveld et (c) : affinement de type LeBail. Tableau R.1 : Paramètres de maile et distances inter-feuillet des phases P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3), Na0.82Mn1/2Fe1/2O2 et O3-Na0.82Mn1/3Fe2/3O2. Figure R.3 : Micrographes (MEB) des phases (a) P2-Na0.67Mn1/2Fe1/2O2 et (b) O3-Na0.82Mn1/3Fe2/3O2. Figure R.4 : Courbes de cyclage galvanostatique (C/50) de batteries enregistrées entre 1.5 et 3.8 V : (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 et (d) O3-Na0.77Mn1/3Fe2/3O2. Un agrandissement autour du point de départ est donné pour chacune des courbes. Figure R.5 : Capacités en décharge extraites des courbes galvanostatiques (Figure R.4) : P2-Na0.66Mn2/3Fe1/3O3 (noir), P2-Na0.62Mn1/2Fe1/2O2 (bleu), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (rouge) et O3-Na0.77Mn1/3Fe2/3O2 (vert).Figure R.6 : (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante. Figure R.7 : Représentation inverse de la Figure R.6. (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante. Figure R.8 : Evolution de (a) la distance inter-feuillet et (b) les paramètres de maille a et b des phases O'3, O3 et P3-NaxMn1-yFeyO2 au cours de la désintercalation électrochimique. (c) Courbe galvanostatique correspondante. Figure R.9 : (a,b) Agrandissement de la région 0.3 ≤ x ≤ 0.7 des diffractogrammes de rayons-X enregistrés in situ (operando) lors de l'expérience menée sur le système de type O3 NaxMn1/3Fe2/3O2. Les lignes rouges mettent en évidence les limites des différents domaines structuraux. Figure R.10 : Représentation schématique de l'évolution du diagramme de phase de NaxMn1-3Fe2/3O2 au cours de la désintercalation électrochimique déduit de l'expérience in situ. Figure R.11 : Diffractogrammes de rayons-X enregistrés in situ pendant une étape potentiostatique (1.5 V) après les (a) première et (b) seconde décharges de l'expérience sur le système NaxMn1/3Fe2/3O2. Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée.Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée. Tableau R.2 : Paramètres Mössbauer correspondant au spectre de O3-Na0.77Mn1/3Fe2/3O2. Tableau R.3 : Formules développées et paramètres Mössbauer correspondant aux affinements des spectres présentés Figure R.13.Les écarts-types sur les valeurs des déplacements isomériques sont égaux à 0.002 mm.s -1 . La population du site Fe (3+z)+ est redistribuée entre les sites Fe 3+ et Fe 4+ selon la formule : P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )). Figure R.14 : Domaines d'observation des phases O'3, O3, P3 et « X » (systèmes de type O3) et des phases P'2, P2 et « Z » (systèmes de type P2) en fonction du taux de Na.Figure R.15 : Evolution des rapports amon./bmon. (phases O'3) et borth./aorth.(phases P'2) en fonction du rapport Mn : Fe. O3-NaFeO2 : données provenant de[35]. O'3-NaMnO2 : données provenant de[44]. Figure R.16 : Evolution des distances M-O des octaèdres MO6 dans les phases P'2 et O'3-Na≈1Mn1-yFeyO2.O'3-NaMnO2 : données provenant de[44].

Figure R. 14 :

 14 Figure R.1 : (a) Structures des phases dites « O3 », « P3 » et « P2 », d'après [36]. Les différents environnements autour des ions Na sont également représentés. (b) Structures distordues (« O'3 », « P'3 » et « P'2 ») dérivant des structures « O3 », « P3 » et « P2 ». Figure R.2 : Diffractogrammes de rayons-X expérimentaux et calculés pour (a) P2-Na0.77Mn2/3Fe1/3O2, (b) P2-Na0.67Mn1/2Fe1/2O2, (c) (O3+O'3)Na0.82Mn1/2Fe1/2O2 et (d) O3-Na0.82Mn1/3Fe2/3O2 phases. Croix rouges : observé, ligne noire : calculé, ligne bleue: différence et barres vertes : Bragg. (a, b, d) : affinement de type Rietveld et (c) : affinement de type LeBail. Tableau R.1 : Paramètres de maile et distances inter-feuillet des phases P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3), Na0.82Mn1/2Fe1/2O2 et O3-Na0.82Mn1/3Fe2/3O2. Figure R.3 : Micrographes (MEB) des phases (a) P2-Na0.67Mn1/2Fe1/2O2 et (b) O3-Na0.82Mn1/3Fe2/3O2. Figure R.4 : Courbes de cyclage galvanostatique (C/50) de batteries enregistrées entre 1.5 et 3.8 V : (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 et (d) O3-Na0.77Mn1/3Fe2/3O2. Un agrandissement autour du point de départ est donné pour chacune des courbes. Figure R.5 : Capacités en décharge extraites des courbes galvanostatiques (Figure R.4) : P2-Na0.66Mn2/3Fe1/3O3 (noir), P2-Na0.62Mn1/2Fe1/2O2 (bleu), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (rouge) et O3-Na0.77Mn1/3Fe2/3O2 (vert).Figure R.6 : (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante. Figure R.7 : Représentation inverse de la Figure R.6. (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante. Figure R.8 : Evolution de (a) la distance inter-feuillet et (b) les paramètres de maille a et b des phases O'3, O3 et P3-NaxMn1-yFeyO2 au cours de la désintercalation électrochimique. (c) Courbe galvanostatique correspondante. Figure R.9 : (a,b) Agrandissement de la région 0.3 ≤ x ≤ 0.7 des diffractogrammes de rayons-X enregistrés in situ (operando) lors de l'expérience menée sur le système de type O3 NaxMn1/3Fe2/3O2. Les lignes rouges mettent en évidence les limites des différents domaines structuraux. Figure R.10 : Représentation schématique de l'évolution du diagramme de phase de NaxMn1-3Fe2/3O2 au cours de la désintercalation électrochimique déduit de l'expérience in situ. Figure R.11 : Diffractogrammes de rayons-X enregistrés in situ pendant une étape potentiostatique (1.5 V) après les (a) première et (b) seconde décharges de l'expérience sur le système NaxMn1/3Fe2/3O2. Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée.Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée. Tableau R.2 : Paramètres Mössbauer correspondant au spectre de O3-Na0.77Mn1/3Fe2/3O2. Tableau R.3 : Formules développées et paramètres Mössbauer correspondant aux affinements des spectres présentés Figure R.13.Les écarts-types sur les valeurs des déplacements isomériques sont égaux à 0.002 mm.s -1 . La population du site Fe (3+z)+ est redistribuée entre les sites Fe 3+ et Fe 4+ selon la formule : P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )). Figure R.14 : Domaines d'observation des phases O'3, O3, P3 et « X » (systèmes de type O3) et des phases P'2, P2 et « Z » (systèmes de type P2) en fonction du taux de Na.Figure R.15 : Evolution des rapports amon./bmon. (phases O'3) et borth./aorth.(phases P'2) en fonction du rapport Mn : Fe. O3-NaFeO2 : données provenant de[35]. O'3-NaMnO2 : données provenant de[44]. Figure R.16 : Evolution des distances M-O des octaèdres MO6 dans les phases P'2 et O'3-Na≈1Mn1-yFeyO2.O'3-NaMnO2 : données provenant de[44].

Figure R. 15 :

 15 Figure R.1 : (a) Structures des phases dites « O3 », « P3 » et « P2 », d'après [36]. Les différents environnements autour des ions Na sont également représentés. (b) Structures distordues (« O'3 », « P'3 » et « P'2 ») dérivant des structures « O3 », « P3 » et « P2 ». Figure R.2 : Diffractogrammes de rayons-X expérimentaux et calculés pour (a) P2-Na0.77Mn2/3Fe1/3O2, (b) P2-Na0.67Mn1/2Fe1/2O2, (c) (O3+O'3)Na0.82Mn1/2Fe1/2O2 et (d) O3-Na0.82Mn1/3Fe2/3O2 phases. Croix rouges : observé, ligne noire : calculé, ligne bleue: différence et barres vertes : Bragg. (a, b, d) : affinement de type Rietveld et (c) : affinement de type LeBail. Tableau R.1 : Paramètres de maile et distances inter-feuillet des phases P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3), Na0.82Mn1/2Fe1/2O2 et O3-Na0.82Mn1/3Fe2/3O2. Figure R.3 : Micrographes (MEB) des phases (a) P2-Na0.67Mn1/2Fe1/2O2 et (b) O3-Na0.82Mn1/3Fe2/3O2. Figure R.4 : Courbes de cyclage galvanostatique (C/50) de batteries enregistrées entre 1.5 et 3.8 V : (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 et (d) O3-Na0.77Mn1/3Fe2/3O2. Un agrandissement autour du point de départ est donné pour chacune des courbes. Figure R.5 : Capacités en décharge extraites des courbes galvanostatiques (Figure R.4) : P2-Na0.66Mn2/3Fe1/3O3 (noir), P2-Na0.62Mn1/2Fe1/2O2 (bleu), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (rouge) et O3-Na0.77Mn1/3Fe2/3O2 (vert).Figure R.6 : (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante. Figure R.7 : Représentation inverse de la Figure R.6. (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante. Figure R.8 : Evolution de (a) la distance inter-feuillet et (b) les paramètres de maille a et b des phases O'3, O3 et P3-NaxMn1-yFeyO2 au cours de la désintercalation électrochimique. (c) Courbe galvanostatique correspondante. Figure R.9 : (a,b) Agrandissement de la région 0.3 ≤ x ≤ 0.7 des diffractogrammes de rayons-X enregistrés in situ (operando) lors de l'expérience menée sur le système de type O3 NaxMn1/3Fe2/3O2. Les lignes rouges mettent en évidence les limites des différents domaines structuraux. Figure R.10 : Représentation schématique de l'évolution du diagramme de phase de NaxMn1-3Fe2/3O2 au cours de la désintercalation électrochimique déduit de l'expérience in situ. Figure R.11 : Diffractogrammes de rayons-X enregistrés in situ pendant une étape potentiostatique (1.5 V) après les (a) première et (b) seconde décharges de l'expérience sur le système NaxMn1/3Fe2/3O2. Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée.Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée. Tableau R.2 : Paramètres Mössbauer correspondant au spectre de O3-Na0.77Mn1/3Fe2/3O2. Tableau R.3 : Formules développées et paramètres Mössbauer correspondant aux affinements des spectres présentés Figure R.13.Les écarts-types sur les valeurs des déplacements isomériques sont égaux à 0.002 mm.s -1 . La population du site Fe (3+z)+ est redistribuée entre les sites Fe 3+ et Fe 4+ selon la formule : P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )). Figure R.14 : Domaines d'observation des phases O'3, O3, P3 et « X » (systèmes de type O3) et des phases P'2, P2 et « Z » (systèmes de type P2) en fonction du taux de Na.Figure R.15 : Evolution des rapports amon./bmon. (phases O'3) et borth./aorth.(phases P'2) en fonction du rapport Mn : Fe. O3-NaFeO2 : données provenant de[35]. O'3-NaMnO2 : données provenant de[44]. Figure R.16 : Evolution des distances M-O des octaèdres MO6 dans les phases P'2 et O'3-Na≈1Mn1-yFeyO2.O'3-NaMnO2 : données provenant de[44].

Figure R. 16 :

 16 Figure R.1 : (a) Structures des phases dites « O3 », « P3 » et « P2 », d'après [36]. Les différents environnements autour des ions Na sont également représentés. (b) Structures distordues (« O'3 », « P'3 » et « P'2 ») dérivant des structures « O3 », « P3 » et « P2 ». Figure R.2 : Diffractogrammes de rayons-X expérimentaux et calculés pour (a) P2-Na0.77Mn2/3Fe1/3O2, (b) P2-Na0.67Mn1/2Fe1/2O2, (c) (O3+O'3)Na0.82Mn1/2Fe1/2O2 et (d) O3-Na0.82Mn1/3Fe2/3O2 phases. Croix rouges : observé, ligne noire : calculé, ligne bleue: différence et barres vertes : Bragg. (a, b, d) : affinement de type Rietveld et (c) : affinement de type LeBail. Tableau R.1 : Paramètres de maile et distances inter-feuillet des phases P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2, (O3+O'3), Na0.82Mn1/2Fe1/2O2 et O3-Na0.82Mn1/3Fe2/3O2. Figure R.3 : Micrographes (MEB) des phases (a) P2-Na0.67Mn1/2Fe1/2O2 et (b) O3-Na0.82Mn1/3Fe2/3O2. Figure R.4 : Courbes de cyclage galvanostatique (C/50) de batteries enregistrées entre 1.5 et 3.8 V : (a) P2-NaxMn0.66Mn1/3Fe2/3O2, (b) P2-Na0.62Mn1/2Fe1/2O2, (c) (O3+O'3)-Na0.77Mn1/2Fe1/2O2 et (d) O3-Na0.77Mn1/3Fe2/3O2. Un agrandissement autour du point de départ est donné pour chacune des courbes. Figure R.5 : Capacités en décharge extraites des courbes galvanostatiques (Figure R.4) : P2-Na0.66Mn2/3Fe1/3O3 (noir), P2-Na0.62Mn1/2Fe1/2O2 (bleu), (O3+O'3)-Na0.77Mn1/2Fe1/2O2 (rouge) et O3-Na0.77Mn1/3Fe2/3O2 (vert).Figure R.6 : (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante. Figure R.7 : Représentation inverse de la Figure R.6. (a) Diffractogrammes de rayons-X enregistrés in situ (operando) pendant la charge d'une cellule NaxMn1/2Fe1/2O2/NaPF6 in PC (1M)/Na. Les diffractogrammes rouges correspondent aux limites des différents domaines structuraux. (b) Courbe galvanostatique correspondante. Figure R.8 : Evolution de (a) la distance inter-feuillet et (b) les paramètres de maille a et b des phases O'3, O3 et P3-NaxMn1-yFeyO2 au cours de la désintercalation électrochimique. (c) Courbe galvanostatique correspondante. Figure R.9 : (a,b) Agrandissement de la région 0.3 ≤ x ≤ 0.7 des diffractogrammes de rayons-X enregistrés in situ (operando) lors de l'expérience menée sur le système de type O3 NaxMn1/3Fe2/3O2. Les lignes rouges mettent en évidence les limites des différents domaines structuraux. Figure R.10 : Représentation schématique de l'évolution du diagramme de phase de NaxMn1-3Fe2/3O2 au cours de la désintercalation électrochimique déduit de l'expérience in situ. Figure R.11 : Diffractogrammes de rayons-X enregistrés in situ pendant une étape potentiostatique (1.5 V) après les (a) première et (b) seconde décharges de l'expérience sur le système NaxMn1/3Fe2/3O2. Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée.Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée. Tableau R.2 : Paramètres Mössbauer correspondant au spectre de O3-Na0.77Mn1/3Fe2/3O2. Tableau R.3 : Formules développées et paramètres Mössbauer correspondant aux affinements des spectres présentés Figure R.13.Les écarts-types sur les valeurs des déplacements isomériques sont égaux à 0.002 mm.s -1 . La population du site Fe (3+z)+ est redistribuée entre les sites Fe 3+ et Fe 4+ selon la formule : P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )). Figure R.14 : Domaines d'observation des phases O'3, O3, P3 et « X » (systèmes de type O3) et des phases P'2, P2 et « Z » (systèmes de type P2) en fonction du taux de Na.Figure R.15 : Evolution des rapports amon./bmon. (phases O'3) et borth./aorth.(phases P'2) en fonction du rapport Mn : Fe. O3-NaFeO2 : données provenant de[35]. O'3-NaMnO2 : données provenant de[44]. Figure R.16 : Evolution des distances M-O des octaèdres MO6 dans les phases P'2 et O'3-Na≈1Mn1-yFeyO2.O'3-NaMnO2 : données provenant de[44].

Figure R. 17 :. 4 :Figure R. 19 :Figure R. 20 : 20 .Figure R. 22 :

 17419202022 Figure R.17 : diffractogrammes observés et calculés (affinement de type Rietveld) de la phase O'3-NaNiO2 (moyens grains). Croix rouges : observé, ligne noire : calculé, ligne bleue : différence et traits verticaux verts : réflexions. Insert : cliché MEB du même échantillon. Tableau R.4 : Paramètres structuraux et facteurs de mérite calculés à partir du diffractogramme de O'3-NaNiO2 (moyens grains).Figure R.18 : (a) courbe galvanostatique et (b) évolution de la capacité en décharge pour une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Régime : C/50.Figure R.19 : Courbe de cyclage en mode GITT enregistrée pour une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Régime : C/50 (pas de 0.005 Na + / unité formulaire), temps de relaxation : 30 minutes.Figure R.20 : Evolution des diffractogrammes de rayons-X enregistré in situ pendant la charge d'une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Les diffractogrammes représentés en rouge correspondent aux composés définis. Figue R.21 : (a,b) Zooms dans le domaine 15,5 -17,3° (2θ Cu kα1) des diffractogrammes présentés Figure R.20. Figure R.22 : Evolution des distances inter-feuillets déduites de la position des pics de diffraction (001)mon. pour les différentes phases NaxNiO2.Figure R.23 : Zoom dans le domaine 15,4 -16,6° (2θ Cu kα1) des diffractogrammes dans le domaine 2/5 ≤ x ≤ 1/2.Figure R.24 : Diffractogrammes correspondant aux composés définis observés pour x = 1, 0.8, 2/3, 1/2, 2/5 et 1/3. Les flèches noires mettent en évidence la présence de pics de diffraction supplémentaires. Figure R.25 : Affinements de type LeBail des profils pour les phases (a) P'3-Na2/3NiO2, (b) P''3-Na1/2NiO2 et (c) O'3-Na2/5NiO2. Le symbole ¤ correspond aux pics de diffractions de NiO. Les indices de Miller noirs et bleus correspondent respectivement aux indexations de la sous-maille et de la sur-maille. Tableau R.5 : Paramètres de maille et groupes d'espaces des super-mailles des composés définis P'3-Na2/3NiO2, P'3-Na1/2NiO2 et O'3-Na2/5NiO2. Les relations entre les paramètres des sur-mailles et des sousmailles sont indiquées en gras.Figure R.26 : Comparaison des diffractogrammes enregistrés lors de l'expérience in situ pour les composés définis (haut) Na≈0.8NiO2 et (bas) O'3-NaNiO2. Les échelles d'intensité des deux diffractogrammes ne sont pas identiques.

Figure R. 24 :Figure R. 25 :. 5 :Figure R. 26 :

 2425526 Figure R.17 : diffractogrammes observés et calculés (affinement de type Rietveld) de la phase O'3-NaNiO2 (moyens grains). Croix rouges : observé, ligne noire : calculé, ligne bleue : différence et traits verticaux verts : réflexions. Insert : cliché MEB du même échantillon. Tableau R.4 : Paramètres structuraux et facteurs de mérite calculés à partir du diffractogramme de O'3-NaNiO2 (moyens grains).Figure R.18 : (a) courbe galvanostatique et (b) évolution de la capacité en décharge pour une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Régime : C/50.Figure R.19 : Courbe de cyclage en mode GITT enregistrée pour une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Régime : C/50 (pas de 0.005 Na + / unité formulaire), temps de relaxation : 30 minutes.Figure R.20 : Evolution des diffractogrammes de rayons-X enregistré in situ pendant la charge d'une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Les diffractogrammes représentés en rouge correspondent aux composés définis. Figue R.21 : (a,b) Zooms dans le domaine 15,5 -17,3° (2θ Cu kα1) des diffractogrammes présentés Figure R.20. Figure R.22 : Evolution des distances inter-feuillets déduites de la position des pics de diffraction (001)mon. pour les différentes phases NaxNiO2.Figure R.23 : Zoom dans le domaine 15,4 -16,6° (2θ Cu kα1) des diffractogrammes dans le domaine 2/5 ≤ x ≤ 1/2.Figure R.24 : Diffractogrammes correspondant aux composés définis observés pour x = 1, 0.8, 2/3, 1/2, 2/5 et 1/3. Les flèches noires mettent en évidence la présence de pics de diffraction supplémentaires. Figure R.25 : Affinements de type LeBail des profils pour les phases (a) P'3-Na2/3NiO2, (b) P''3-Na1/2NiO2 et (c) O'3-Na2/5NiO2. Le symbole ¤ correspond aux pics de diffractions de NiO. Les indices de Miller noirs et bleus correspondent respectivement aux indexations de la sous-maille et de la sur-maille. Tableau R.5 : Paramètres de maille et groupes d'espaces des super-mailles des composés définis P'3-Na2/3NiO2, P'3-Na1/2NiO2 et O'3-Na2/5NiO2. Les relations entre les paramètres des sur-mailles et des sousmailles sont indiquées en gras.Figure R.26 : Comparaison des diffractogrammes enregistrés lors de l'expérience in situ pour les composés définis (haut) Na≈0.8NiO2 et (bas) O'3-NaNiO2. Les échelles d'intensité des deux diffractogrammes ne sont pas identiques.

  , resulting in better electrochemical properties. Recently, Kim et al. and Xu et al. studied the impact of Li substitutions

Table I .7. Table I.7 only

 I

sums up the advanced electrochemical studies carried out on the displayed materials. Several preliminary studies reported the synthesis of the materials or the possibility to reversibly intercalate and deintercalate Na + ions. Hence, Xia et al. and Paulsen et al., studied the structure of several NaxMn1-yNiyO2 materials [74, 80]. Lu and Dahn published an in situ XRPD study of the P2-Na2/3Mn2/3Ni1/3O2 phase diagram and suggested the P2 → O2 phase transiion for xNa < 1/3 in 2001 [72].

Table I .

 I 7a: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple.

	NaxMO2 material	Studied E range	Discharged capacity (C-rate)	Capacity retention 5	References
			NaxFe1-yNiyO2
	O3-NaFe1/2Ni1/2O2	2.0 -3.8 V	112 mAh.g -1 (C/8)	55 % (30 cycles)	[67]
	O3-NaFe0.3Ni0.7O2	2.0 -3.8 V	135 mAh.g -1 (C/8)	74 % (30 cycles)	[67]
		NaxNi1-y-zCoyFezO2
	O3-NaNi1/3Co1/3Fe1/3O2	2.0 -4.2 V	165 mAh.g -1 (C/20)	91 % (20 cycles)	[68]
		NaxNi1-y-zMnyFezO2
	O3-NaNi1/3Mn1/3Fe1/3O2	1.5 -4.0 V	≈ 130 mAh.g -1 (C/2)	77% (150 cycles)	[46]
	O3-NaNi0.3Mn0.3Fe0.4O2	2.0 -3.8 V ≈ 135 mAh.g -1 (C/20)	80 % (50 cycles)	[69]
	O3-NaNi0.2Mn0.2Fe0.6O2	20) 2.0 -3.8 V ≈ 135 mAh.g -1 (C/20)	93 % (10 cycles) 60 % (50 cycles)	[66] [69]
	P2-Na0.67Ni0.15Mn0.65Fe0.2O2	1.5 -4.3 V	≈ 150 mAh.g -1 (C/10) 208 mAh.g -1 (C/20)	93 % (20 cycles) 71 % (50 cycles)	[30] [86]
			≈ 204 mAh.g -1 (C/20)	75 % (40 cycles)	[32]
	P2-Na2/3Mn0.65Fe0.35O2	1.5 -4.3 V ≈ 208 mAh.g -1 (C/20)	67 % (30 cycles)	[86]
	P2-NaxMn1/2Fe1/2O2	1.5 -4.2 V 1.5 -4.3 V	190 mAh.g -1 (C/20) 160 mAh.g -1 (C/10)	74 % (30 cycles) 56 % (40 cycles)	[26, 28] [33]
	O3-NaMn1/2Fe1/2O2	1.5 -4.2 V	≈ 110 mAh.g -1 (C/20)	68 % (30 cycles)	[26]
	O3-NaMn1/3Fe2/3O2	2.0 -3.8 V	≈ 100 mAh.g -1 (C/20)	93 % (10 cycles)	[66]
		NaxMn1-yCoyO2
	P2-Na0.7Mn0.89Co0.11O2	1.5 -3.8 V	138 mAh.g -1 (C/3)	67 % (20 cycles)	[87]
	P2-Na2/3Mn1/2Co1/2O2	1.5 -4.0 V	123 mAh.g -1 (C/8)	69 % (30 cycles)	[88]
	P2-Na0.79Mn0.3Co0.7O2	2.0 -3.8 V	60 mAh.g -1 (C/2)	87 % (60 cycles)	[89]
			-40-

Table I .

 I 7b: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple.

				94 % (20 cycles)
			20)	82 % (20 cycles)	[90]
			≈ 190 mAh.g -1 (C/20)	54 % (10 cycles)
	P2-Na0.45Ni0.22Mn0.66Co0.11O2	2.1 -4.2 V ≈ 140 mAh.g -1 (C/10)	72 % (275 cycles)	[91, 92]
	P2-Na2/3Ni0.15Mn0.65Co0.2O2	2.0 -4.4 V ≈ 140 mAh.g -1 (C/12)	90 % (50 cycles)	[93]
	P2-Na0.7Ni1/9Mn2/9Co2/3O2	2.0 -4.2 V 2.0 -4.5 V	≈ 110 mAh.g -1 (C/20) ≈ 140 mAh.g -1 (C/20)	89 % (90 cycles) 86 % (10 cycles)	[94]
	O3-NaNi1/3Mn1/3Co1/3O2	2.0 -3.75 V	120 mAh.g -1 (1C)	75 % (50 cycles)	[95]
		NaxNi1-y-z-wMnyCozAlwO2
	P2-Na2/3Ni0.15Mn0.65Co0.15Al0.05O2 2.0 -4.4 V ≈ 130 mAh.g -1 (C/12) 95.4 % (50 cycles)	[93]
		NaxNi1-y-zMnyLizO2
	P2-Na0.80Ni0.22Mn0.66Li0.12O2	2.0 -4.4 V	133 mAh.g -1 (C/10)	91 % (50 cycles)	[70]

Table I .

 I

7 highlights some interesting tendencies:

table :

 :

		XRPD		S-XRPD	S-XRPD
		Nax(Mn,Fe)O2	NaxNiO2	ESRF	APS
	Nature	glass	glass	glass	polyimide
	Inner diameter	0.1 mm	0.3 mm	1.0 mm	1.0 mm
	Sealing	flame	flame	glue (epoxy)	glue (epoxy)
	λ	Cu kα1,2		0.399845 Å	0.413913 Å
	2θ range	10 -120°		3-44°	1-60°

Table II . 1 :

 II1 Experimental conditions concerning the XRPD and Synchrotron XRPD experiments carried out in this work.

Experimental: Operando in situ XAS

	All the measurements were carried out on the 17C beam line at National Synchrotron Radiation
	Research Center (NSRRC) in Taiwan, R.O.C. in collaboration with the group of Pr. Bing Joe Hwang of
	National Taiwan University of Science and Technology (NTUST). These measurements were part of the
	ANR project LaNaMox between ICMCB and NTUST.
	Its fit necessitates known reference materials and a
	good description of the structure. Once all parameters are known, it is possible to use Fourier
	transformation on the EXAFS spectra to determine the distances between the absorbing atom and the
	nearest neighbors [108].
	-61-

  ................................................................................... A-I.3.b. Morphology ....................................................................................................................... A-I.3.c. Electrochemistry ................................................................................................................

	-66-

P2-Na0.77Mn2/3 Fe1/3O2 P2-Na0.67Mn1/2 Fe1/2O2 (O3+O'3)Na0.82Mn1/2 Fe1/2O2 O3-Na0.82Mn1/3 Fe2/3O2 Space group

			a) P2-Na 0.77 Mn 2/3 Fe 1/3 O 2						b) P2-Na 0.67 Mn 1/2 Fe 1/2 O 2
	(002)											(002)
	Intensity (A.U.)		(004)	(100) (101) (102)	(103)	(104) (006)	(105)	(106) (110)	(112)	(008)		Intensity (A.U.)		(004)	(100) (101) (102)	(103)	(104) (006)	(105)	(106) (110)	(112) (008)
	10	20	30	40		50		60		70	80	10	20	30	40		50	60	70	80
				2θ (°) Cu kα 1,2								2θ (°) Cu kα 1,2
		c) (O3+O'3)-Na 0.82 Mn 1/2 Fe 1/2 O 2					d) O3-Na 0.82 Mn 1/3 Fe 2/3 O 2
												(003)			(104)
	Intensity (A.U.)											Intensity (A.U.)		(006)	(101) (102)	(105)	(009)	(107)	(108)	(110)	(113)	(1 0 10) (0 0 12)
		O3 phase O'3 phase
	10	20	30	40		50		60		70	80	10	20	30	40		50	60	70	80
				2θ (°) Cu kα 1,2								2θ (°) Cu kα 1,2
				P63/mmc				P63/mmc	R-3m (O3) C2/m (O'3)	R-3m
	a (Å)			2.9392(1)			2.9386(1)	2.9730(3)	5.2170(7)	2.9805(1)
	b (Å)				/					/		/		2.9462(3)	/
	c (Å)			11.1648(6)			11.1884(4)	16.396(4)	5.7515(8)	16.3264(5)
	β (°)				/					/		/		108.24(1)	/
	Interslab distance (Å)		5.5824(6)			5.5942(4)	5.465(4)	5.463(3)		5.4421(5)
	Table A-I.1: Cell parameters and Interslab distances of the P2-Na0.77Mn2/3Fe1/3O2, P2-Na0.67Mn1/2Fe1/2O2,
	(O3+O'3)Na0.82Mn1/2Fe1/2O2 and O3-Na0.82Mn1/3Fe2/3O2 phases.

Table A-I.2. The

  Rietveld refinements of the structures of the different materials will be detailed in

Chapters A-II and A-III. Targeted NaxMn1-yFeyO2 material Na: (Mn + Fe) ratio (ICP-AES) Mn: (Mn + Fe) ratio (ICP-AES) Fe: (Mn + Fe) ratio (ICP-AES) Na:(Mn + Fe) ratio (Rietveld)

	P2-Na0.77Mn2/3Fe1/3O2	0.77(2)	0.64(2)	0.36(2)	0.66(2)
	P2-Na0.67Mn1/2Fe1/2O2	0.66(2)	0.47(2)	0.53(2)	0.62(1)
	O3-Na0.82Mn1/2Fe1/2O2	0.81(2)	0.47(2)	0.53(2)	Undetermined
	O3-Na0.82Mn1/3Fe2/3O2	0.83(2)	0.31(2)	0.69(2)	0.77(1)

Table A-I.2: ICP-AES results for the pristine materials synthesized by self-combustion synthesis. Table A-I.2 shows that the targeted sodium compositions and transition metal contents are confirmed

  by ICP-AES analysis in the range of experimental errors, confirming that the 10 wt% of excess

Table A -

 A

II.2: Structural parameters and reliability factors calculated from the combined refinement of the O3-Na0.77Mn1/3Fe2/3O2 pristine material based on the XRPD and neutron powder diffraction patterns.

  30 31 32 33 34 35 36 37 38 39 40 41 42 43 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Table A -

 A II.3: Structural parameters and reliability factors calculated from the refinement of the structure of the O'3 phase from the synchrotron XRPD pattern.

				2θ Cu kα 1
		10 15 20 25 30 35 40 45 50 55 60 65 70
	Intensity (A. U.)	(001)	*	(002)	(200) (-111) (110) (-201)	(111) (-202)	(201) (-112)	(003)	(-203)	(112) *	(-113)	(-311) (020) (202)
		3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
			2θ (°) λ = 0.399845 Å
	O'3

-Na 0.96 Mn 1/3 Fe 2/3 O 2

  To prepare the O3-Na2/3Mn1/3Fe2/3O2 material we targeted the middle of the voltage jump on the E = f(x) curve (Eeq = 2.8 V, x = 0.67). According to the in situ XRPD study, we expect a pure O3 phase. The calculated and observed Synchrotron XRPD patterns are represented in Figure A-II.14. The corresponding cell and atomic parameters are given in Table A-II.4.

	The O3-Na2/3Mn1/3Fe2/3O2 phase
	The synchrotron XRPD data shows a pure O3 phase whose structure and cell parameters are
	comparable to the starting one. The chex. and ahex. cell parameters are larger (16.545(1) Å vs. 16.3420(2) Å)
	and smaller (2.9589(1) Å vs. 2.9820(1) Å) respectively than those of the pristine material, in agreement
	with the lower Na content (x = 0.67 vs. x = 0.77 initially). Moreover, it is noteworthy that no extra-
	diffraction lines resulting from sodium/vacancy ordering are observed, as it is the case for several
	Na2/3MO2 materials with only one type of transition metal [48, 55, 56].
	Space group : C2/m
	a mon. = 5.3447(5) Å, b mon. = 2.9717(2) Å, c mon. = 5.6858(5) Å, β mon. = 109.48(1)°a mon. /b mon. = 1.80
	Atom	Wyckoff	Coordinates		Occupancy	ADP (Ų)
	Na	2c	0	0	1/2	0.96(2)	0.5(3)
	Mn Fe	2b 2b	0 0	1/2 1/2	0 0	1/3 2/3	0.3(1)
	O	4i	0.227(3)	0	0.202(2)	1	0.5(3)
	M-O distances		4 * 2.02(1) Å		2 * 2.14(2) Å
	Rwp = 11.41%; R B = 2.44% (with excluded regions)
			-101-

O3-Na 0.67 Mn 1/3 Fe 2/3 O 2

	Space group: R-3m
	a hex. = 2.9591(1) Å, c hex. = 16.545(1) Å
	Atom	Wyckoff		Coordinates		Occupancy	ADP (Ų)
	Na	3b	0	0	1/2	0.67(1)	2.4(2)
	Mn Fe	3a 3a	0 0	0 0	0 0	1/3 2/3	0.53(3)
	O	6c	0	0	0.2701(2)	1	0.77(8)
	M-O distances	6 * 2.00(1) Å
	Rwp = 8.40%; R B = 5.91% (with excluded regions)
				-103-

Table A -

 A II.5: Structural parameters and reliability factors calculated from the refinement of the structure of the P3 phase from the synchrotron XRPD pattern.

				2θ Cu kα 1
	10 15 20 25 30 35 40 45 50 55 60 65 70
		(003)
	Intensity (A. U.)	* P3 phase	(006)	(101) (102)	(104)	(105)	(009)	(107)	*	(108)	(110)	(113) (0 0 12) (1 0 10)
		O3 phase
	3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
			2θ (°) λ = 0.399845 Å
	P3-Na 0.61 Mn 1/3 Fe 2/3 O 2 Space group: R-3m
	a hex. = 2.9338(1) Å, c hex. = 16.913(1) Å
	Atom	Wyckoff			Coordinates					Occupancy	ADP (Ų)
	Na	6c	0		0			0.168(1)		0.61(3)	3.0(7)
	Mn Fe	3a 3a	0 0		0 0			0 0			1/3 2/3	0.44(5)
	O	6c	0		0			0.394(1)		1	0.7(2)
	M-O distances	6 * 1.99 (1) Å
	Rwp = 11.82%; R B = 6.35% (with excluded regions)
					-104-

  As discussed in Chapter A-I, the starting point of the curve (x = 0.77) is located on the voltage plateau, in agreement with the fact that two phases are present in the pristine material (O3 and O'3). This plateau is observed in the 0.77 ≤ x ≤ 0.9 Na range upon intercalation and is reversible. Upon deintercalation, a voltage overshoot is observed at x = 0.91, indicating that the intercalated phase (presumably O'3) is highly resistive. After the voltage plateau (x > 0.77), the voltage continuously increases and mark a smooth voltage jump at x ≈ 0.55, corresponding to the change of the active redox couple from Mn 4+ /Mn 3+ to Fe 4+ /Fe 3+ . Then, the polarization decreases and the voltage continuously increases up to E ≈ 3.95 V where a voltage plateau is observed for 0.25 ≤ x ≤ 0.33. After this voltage plateau, the polarization gradually increases up to 4.3 V. Comparing to the GITT cycling curve of the NaxMn1/3Fe2/3O2 system for which the voltage jump occurs at x ≈ 0.67 in good agreement with the change in the redox process, we observe the voltage jump at x ≈ 0.55 instead of x = 0.5 for the NaxMn1/2Fe1/2O2 system. Moreover, the voltage jump is quite smooth instead of marking a sudden jump as for the NaxMn1/3Fe2/3O2 composition. It is impossible to give any explanation on this phenomenon based on the GITT curve only.

		4.2
		4.0
		3.8
		3.6
		3.4
		3.2
	E (V)	2.6 2.8 3.0
		2.4
		2.2
		2.0				(O3+O'3)-Na 0.77 Mn 1/2 Fe 1/2 O 2
		1.8
		1.6
		1.4	a)
		0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1.0
						x in Na x Mn 1/2 Fe 1/2 O 2
		4.2
		4.0
		3.8
		3.6
		3.4
		3.2
	E (V)	2.6 2.8 3.0
		2.4
		2.2
		2.0					O3-Na 0.77 Mn 1/3 Fe 2/3 O 2
		1.8
		1.6
		1.4	b)
		0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1.0
						x in Na x Mn 1/3 Fe 2/3 O 2
							-108-

  3.45+ (Na0.55FeO2) are given in (f).

							Na x Mn 1/3 Fe 2/3 O 2
	a) Mn K-edge						b) Fe K-edge
				x=0.93 x=0.80 x=0.68 x=0.60 x=0.41							x=0.93 x=0.80 x=0.68 x=0.60 x=0.41
	6535	6540	6545	6550	6555	6560	6565	6570	7110	7115	7120	7125	7130	7135	7140	7145
				Energy (eV)							Energy (eV)
							Na x Mn 1/2 Fe 1/2 O 2
	c) Mn K-edge	x=0.91 x=0.83				d) Fe K-edge	x=0.91 x=0.83
				x=0.70 x=0.62 x=0.51 x=0.46						x=0.70 x=0.62 x=0.51 x=0.46
	6535	6540	6545	6550	6555	6560	6565	6570	7110	7115	7120	7125	7130	7135	7140	7145
				Energy (eV)							Energy (eV)
								References
	e) Mn K-edge: references				f) Fe K-edge: references
			Mn 2 O 3							FeO
											Fe 2 O 3
			Li 2 MnO 3							Na 0.55 FeO 2 Na 1 FeO 2
	6535	6540	6545	6550	6555	6560	6565	6570	7110	7115	7120	7125	7130	7135	7140	7145
				Energy (eV)							Energy (eV)
								-120-

Table A

 A

					Velocity (mm.s -1 )
		-4	-3	-2	-1	0	1	2	3	4
								Na 0.77 Mn 1/3 Fe 2/3 O 2
								(pristine material)
		a)
	Absorption (A.U.)	-4	-3	-2	-1	0	1	2 Na 0.96 Mn 1/3 Fe 2/3 O 2 3 Na 0.85 Mn 1/3 Fe 2/3 O 2 Na 0.67 Mn 1/3 Fe 2/3 O 2	4
								Na 0.58 Mn 1/3 Fe 2/3 O 2
								Na 0.38 Mn 1/3 Fe 2/3 O 2
		b)
		Site		δ (mm.s -1 )	FWHM (mm.s -1 )	Δ (mm.s -1 )		P (%)
		Fe 3+ (A)	0.353	0.30		0.88		25
		Fe 3+ (B)	0.354	0.35		0.58		75
	-II.7: Mössbauer parameters corresponding to the spectrum of the O3-Na0.77Mn1/3Fe2/3O2 pristine
	material.
					-122-

Na 0.96 Mn 3+ 0.29 Mn 4+ 0.04 Fe 3+

				Fe 3+ (1) Δ* (mm.s -1 ) δ (mm.s -1 )	P (%)	Fe 3+ (2) Δ* (mm.s -1 ) δ (mm.s -1 )	P (%)				Δ max (mm.s -1 )	%Fe 3+ %Fe 4+
	0.67 Fe 4+ 0 O 2 100	0	0.355	1.00	40 0.365	0.71	60				0.93	100	0
	Na 0.85 Mn 3+ 0.15 Mn 4+ 0.18 Fe 3+ 0.67 Fe 4+ 0 O 2 100	0	0.351	0.81	39 0.360	0.61	61				0.80	100	0
	Na 0.67 Mn 3+ 0 Mn 4+ 0.33 Fe 3+ 0.67 Fe 4+ 0 O 2	100	0	0.341	0.78	41 0.360	0.67	59				0.67	100	0
					Fe 3+			Fe 4+				Fe (3+z)+
	Developed formula	%Fe 3+ %Fe 4+	δ (mm.s -1 )	Δ* (mm.s -1 )	P (%)	δ (mm.s -1 )	Δ* (mm.s -1 )	P (%)	δ (mm.s -1 )	Δ* (mm.s -1 )	P (%)	Δ max (mm.s -1 )	%Fe 3+ %Fe 4+

Repartition between Fe 3+ (%) Fe 4+ (%) Na 0.58 Mn 3+ 0 Mn 4+ 0.33 Fe 3+ 0.58 Fe 4+ 0.09 O 2 87

		13	0.336	0.70	78	0.04	0.19	3	0.175	0.68	19	9	10	0.70	87	13
	Na 0.38 Mn 3+ 0 Mn 4+ 0.33 Fe 3+ 0.38 Fe 4+ 0.29 O 2 57	43	0.321	0.87	57 0.048	0.55	24 0.107	0.77	19	4	15	0.87	61	39

Table A -

 A

II.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra presented in Figure A-II.27b

Table A -

 A II.8, the population of the Fe 4+ site increases as the one of the Fe 3+ site decreases upon Na + deintercalation. The third site shows an intermediate isomer shift between Fe 3+ and Fe 4+ . We associated this site to an intermediate Fe (3+z)+ oxidation state that can result from fast electron hopping between the Fe 3+ and Fe 4+ ions, as already observed in the LixNi0.70Fe0.15Co0.15O2 system[START_REF] Prado | [END_REF] and -126-in the Ni1-yFeyOOHx / Ni1-yFey(OH)2 one, both ex [122] and in situ [123]. This intermediate Fe (3+z)+ oxidation

Repartition between Fe 3+ (%) Fe 4+ (%) Na 0.44 Mn 3+ 0 Mn 4+ 0.50 Fe 3+

		Awaited results from electrochemistry									Mössbauer results (Lorentzian fit)
					Velocity (mm.s -1 ) Fe 3+ (A)				Fe 3+ (B)
	-4	-3 Developed formula -2	-1 %Fe 3+ %Fe 4+ 0	δ	1 Δ	Γ	2	P	δ	3	Δ	4 Γ	P	%Fe 3+ %Fe 4+
								(mm.s -1 )	(mm.s -1 )	(mm.s -1 )	(%)	(mm.s -1 )	(mm.s -1 )	(mm.s -1 )	(%)
		Na 0.95 Mn 3+ 0.45 Mn 4+ 0.05 Fe 3+ 0.50 Fe 4+ 0 O 2 100	0			0.345	0.96	0.37		44 0.344	0.64	0.33	56	100	0
		Na 0.67 Mn 3+ 0.17 Mn 4+ 0.33 Fe 3+ 0.50 Fe 4+ 0 O 2 100	0			0.338	0.86	0.31	Na 0.95 Mn 1/2 Fe 1/2 O 2 46 0.343 0.62	0.29	54	100	0
		Na 0.55 Mn 3+ 0.05 Mn 4+ 0.45 Fe 3+ 0.50 Fe 4+ 0 O 2 100	0			0.339	0.90	0.33		57 0.340	0.62	0.28	43	100	0
	Absorption (A.U.) -131-	Developed formula 0.44 Fe 4+ 0.06 O 2 88 %Fe 3+ %Fe 4+ 12 Developed formula %Fe 3+ %Fe 4+	δ (mm.s -1 ) 0.336 δ (mm.s -1 )	Fe 3+ Δ (mm.s -1 ) 0.94 Fe 3+ Δ* (mm.s -1 )	Na 0.55 Mn 1/2 Fe 1/2 O 2 Na 0.67 Mn 1/2 Fe 1/2 O 2 Fe 4+ (mm.s -1 ) Γ P (%) δ (mm.s -1 ) Δ (mm.s -1 ) (mm.s -1 ) Γ 0.31 37 0.03 0.1 0.24 Mössbauer results (Distribution fit) P (%) δ (mm.s -1 ) Δ (mm.s -1 ) 2 0.321 0.72 Fe 4+ Na 0.44 Mn 1/2 Fe 1/2 O 2 Γ P δ Δ* Γ P δ Δ* (mm.s -1 ) (%) (mm.s -1 ) (mm.s -1 ) (mm.s -1 ) (%) (mm.s -1 ) (mm.s -1 )	Fe (3+z)+ Γ (mm.s -1 ) P (%) 0.24 61 Fe (3+z)+ Γ P (mm.s -1 ) (%)	58	3	%Fe 3+ %Fe 4+ 95 5 %Fe 3+ %Fe 4+
												Na 0.22 Mn 1/2 Fe 1/2 O 2
									d) Na 0.44 Mn 1/2 Fe 1/2 O 2
										Lorentzian fit
					Velocity (mm.s -1 )
			-4	-3	-2	-1	0		1	2	3	4
			0
			1
		Absorption (%)	3 2
			4
			e) Na 0.22 Mn 1/2 Fe 1/2 O 2
			5	Distribution fit
						-130-

Figure A-II.30: Comparison of the Mössbauer spectra recorded for the NaxMn1/2Fe1/2O2 system. Black dots: experimental and red line: calculated.

Repartition between Fe 3+ (%) Fe 4+ (%) Na 0.22 Mn 3+ 0 Mn 4+ 0.50 Fe 3+

	0.22 Fe 4+ 0.28 O 2 44	56	0.35	0.90	0.25	52	0.02	0.64	0.25	18	0.20	0.94	0.25	30	16	14	68	32

Table A

 A

			2θ (°) Cu kα 1
		10 15 20 25 30 35 40 45 50 55 60 65 70
		(002)
	Intensity (A. U.)		(004)	(100) (101)	(102)	(103)	(104) (006)	(105)	(106)	(110)	(112) (008)
		3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
			2θ (°) λ = 0.41391 Å
	Space group: P6 3 /mmc a hex. = 2.9405(1) Å, c hex. = 11.1957(2) Å
	Atom	Wyckoff		Coordinates		Occupancy ADP (Ų)
	Na f	2d	0	0		1/4	0.18(1)	1.8(7)
	Na e	2b	2/3	1/3		1/4	0.44(2)	1.9(4)
	Mn Fe	2a 2a	0 0	0 0		0 0		1			0.29(3)
	O	4f	1/3	2/3		0.093(1) 1			0.7(1)
	Distances:	M-O		Na-O
		6 * 1.99(1) Å	6 * 2.44(1) Å
	Rwp = 15.33%; R B = 8.93%
	-III.1: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern
	of P2-Na0.62Mn1/2Fe1/2O2.
				-136-

Table A -

 A III.2: Structural parameters and reliability factors calculated from the combined refinement of P2-Na0.62Mn1/2Fe1/2O2 from the XRPD and neutron powder diffraction patterns.

  Moreover for x = 0.5 the polarization is quite high because, at this exact composition, there is only Mn 4+

		4.2
		4.0
		3.8
		3.6
		3.4
		3.2
	E (V)	2.6 2.8 3.0		3.8 3.4 3.6					P2-Na 0.62 Mn 1/2 Fe 1/2 O 2
		2.2 2.4	E (V)	3.0 3.2	x = 0.48
		2.0		2.8
		1.8		2.6		x = 0.52
		1.6		125 120 115 110 105 100 95 2.4	90
		1.4				time (h)
		.1		0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1.0
						x in Na x Mn 1/2 Fe 1/2 O 2
							-144-

Table A

 A The synchrotron XRPD pattern is successfully indexed in the Cmcm orthorhombic space group of the P'2 structures. The refined Na content is equal to 1.0(2), in agreement with the one obtained from electrochemical characterizations. The borth./a orth. ratio(1.84) shows the distortion induced by the cooperative Jahn-Teller effect. It is confirmed by the distortion of the MO6 octahedra which possess 4 short

		10 15 20 25 30 35 40 45 50 55 60 65 70 2θ (°) Cu kα 1
		(002)
	M-O distances (1.99(6) Å) and 2 long ones (2.18(1) Å) (Table A-III.3).
	Intensity (A. U.)		*	(004) (020)	(110) (021)	(112) (111) (022)	(023)	(113)	(024) (114) (006)	(025) (115) *	(130)	(131) (026) (116) (132) (200) (202) (133)	(008) (040)
		3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
				2θ (°) λ = 0.39985 Å
	Space group: Cmcm
	a orth. = 2.9367(2) Å, b orth. = 5.4015(5) Å, c orth. = 10.8248(8) Å
	b orth. /a orth. = 1.84
	Atom	Wyckoff		Coordinates		Occupancy ADP (Ų)
	Na e	4c	0	0.683(2)		1/4		1.0(2)	0.7(2)
	Mn Fe	4a 4a	0 0		0 0			0 0		1		0.60(5)
	O	8f	0	0.648(2) 0.901(1)		1		0.5(2)
	Distances : M-O		Na-O
		4 * 1.99(1) Å		4 * 2.38(1) Å
		2 * 2.18(1) Å		2 * 2.42(1) Å
	Rwp = 8.40 %; R B = 7.13 % with excluded regions (graphite)
	-III.3: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern
	of the P'2-Na≈1Mn1/2Fe1/2O2 phase.
					-151-

Table A

 A

			2θ (°) Cu kα 1
		10 15 20 25 30 35 40 45 50 55 60 65 70
		(002)
	Intensity (A. U.)		(004)	(100) (101)	(102)	(103)	(104) (006)	(105)	(106)	(110)	(112)
		3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
			2θ (°) λ = 0.41391 Å
	Space group: P6 3 /mmc
	a hex. = 2.9400(1) Å, c hex. = 11.1812(6) Å
	Atom	Wyckoff		Coordinates			Occupancy ADP (Ų)
	Na f Na e	2d 2b	0 2/3	0 1/3		1/4 1/4		0.20(2) 0.46(2)	2.9(5)
	Mn Fe	2a 2a	0 0		0 0		0 0			1	0.65(4)
	O	4f	1/3	2/3	0.093(1)		1	1.1(1)
	Distances:	M-O		Na-O
		6 * 1.99(1) Å		6 * 2.44(1) Å
	Rwp = 13.29%; R B = 5.73%
	-III.4: Structural parameters and reliability factors calculated from the synchrotron XRPD pattern
	of the P2-Na0.66Mn2/3Fe1/3O2 pristine material.
				-154-

Table A -

 A III.5: Structural parameters and reliability factors calculated from the combined refinement of the P2-Na0.66Mn2/3Fe1/3O2 pristine material from the XRPD and neutron powder diffraction patterns.

  We then studied the influence of the rate on the discharge capacity of the P2-Na0.66Mn2/3Fe1/3O2 material. The experiment consisted in different series of 3 cycles, realized with the following rate values:The low discharge capacity reached at the 19 th cycle at C/20 is due to the low amount of Na + ions intercalated during the previous charge carried out at 2C.

		4.2		Influence of the rate
		4.0
		3.8
	3.4 3.6 C/20, C/10, C/5, C/5, C, 2C and again at C/20. The corresponding evolution of the discharge capacity is
	3.2 shown in Figure A-III.19.
	E (V)	2.6 2.8 3.0
		2.4
		2.2
		1.8 2.0				P2-Na 0.66 Mn 2/3 Fe 1/3 O 2
		1.6
		1.4	a)
		0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1.0
						x in Na x Mn 2/3 Fe 1/3 O 2
		4.2
		4.0
		3.8
		3.6
		3.4
		3.2
	E (V)	2.6 2.8 3.0
		2.4
		2.2
		2.0			P2-Na 0.62 Mn 1/2 Fe 1/2 O 2
		1.8
		1.6
		1.4	b)
			1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1.0
						x in Na x Mn 1/2 Fe 1/2 O 2
							-159-

Figure A-III.19: Evolution of the discharge capacity of the NaxMn2/3Fe1/3O2 system for several rate values.

As for the P2-NaxMn1/2Fe1/2O2 system, increasing the rate to C/10 or C/5 does not induce an important capacity loss, and 84% of the initial discharge capacity is still accessible at C/5. On the other hand, cycling at higher rate values leads to an important capacity loss as only 56 %, 28 % and 16 % of the initial discharge capacity are reached at C/2, C and 2C. When the material is cycled back at C/20, 92% of the initial discharge capacity is reached after one cycle. This indicates that the material does not undergo any damage upon cycling at high rate. The observed capacity loss is therefore only due to kinetic effects.

  The comparison of this in situ experiment with the one carried out on NaxMn1/2Fe1/2O2 shows that both systems exhibit similar behavior. The only difference is the occurrence of the intermediate P'2i phase between the P'2f fully intercalated and P2 ones.

				(hkl) P'2f : reflections of the fully-intercalated P'2 phase
				(hkl) P'2i : reflections of the intermediate P'2 phase
				(hkl) P2 : reflections of the P2 phase
		a) The indexation of the XRPD diagrams presented in Figures A-III	b)
																0.1
																0.20	0.2
	P'2 i P2	(002) P2 (002) P'2i		(004) P2 (004) P'2i			(100) P2 (110) P'2i		(022) P'2i	(102) P2 (112) P'2i 0.74	0.94 0.68 0.76	0.9 0.8 0.7 0.6 0.5 0.4 0.3	x in Na x Mn 2/3 Fe 1/3 O 2
	P'2 f	(002) P'2f	(020) P'2f	(004) P'2f	(110) P'2f	(022) P'2f		(112) P'2f	0.96	1.0
		16	17	18 31	32	33		34	35	36	37	38	39	40	3	2
					2θ (°) Cu kα 1,2							E (V)
		P'2f (002)		(hkl) P'2f : reflections of the fully-intercalated P'2 phase (hkl) P'2i : reflections of the intermediate P'2 phase (hkl) P2 : reflections of the P2 phase
							P'2f
	(002) P'2i a) P'2 f		(004) P'2i	P'2f (020)	(004)	(110) P'2i	(110) P'2f		(022) P'2f	P'2i (022)	(112) P'2f	(112) P'2i b)	0.96 0.94	0.9 1.0
	(002) P2 P'2 i P2		(004) P2					(100) P2					0.74 (102) P2	0.68 0.76	0.3 0.4 0.5 0.6 0.7 0.8	x in Na x Mn 2/3 Fe 1/3 O 2
																0.20	0.2
																0.1
		16	17	18 31	32	33		34	35	36	37	38	39	40	4	3	2
					2θ (°) Cu kα 1,2							E (V)
									-162-

Table A

 A

	(002)
	Intensity (A. U.)	*	(020) (004)	(110) (021)	(112) (111) (022)	(023)	(113)	(024) (114)	(006)	(025) (115) *	(130)	(200) (026) (131) (132) (116)
	10 15 20 25 30 35 40 45 50 55 60 65 70
			2θ (°) Cu kα 1,2
	Space group: Cmcm
	a orth.
	-III.6: Structural parameters and reliability factors calculated from the XRPD diagram of the P'2-
	Na0.96Mn2/3Fe1/3O2 phase.

Operando in situ x-ray absorption near edge spectroscopy study of the NaxMn1/2Fe1/2O2 system

		4.2
		4.0
		3.8
		3.6
		3.4
		3.2
	E (V)	2.6 2.8 3.0
		2.4
		2.2
		2.0
		1.8
		1.6	Na x Mn 1/2 Fe 1/2 O 2
		1.4	Na x Mn 2/3 Fe 1/3 O 2
		0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1.0
							1-y Fe y O 2

A-III.3.a.

Table A -

 A III.7: Mössbauer parameters deduced from the Lorentzian and Distribution fits of the Mössbauer spectrum of the P2-Na0.62Mn1/2Fe1/2O2 pristine material.

			a) Lorentzian fit
	Site	δ (mm.s -1 )	FWHM (mm.s -1 )	Δ (mm.s -1 )	P (%)
	Fe 3+ (A)	0.356	0.35	0.67	100
			b

) Distribution fit Site δ (mm.s -1 ) FWHM (mm.s -1 ) Δ* (mm.s -1 ) P (%)

	Fe 3+ (1)	0.356 (fixed)	0.25 (fixed)	0.70	100
			-173-

Table A -

 A

				Velocity (mm.s -1 )
	-4	-3	-2	-1	0	1	2	3	4
							P'2-Na ≈1 Mn 1/2 Fe 1/2 O 2
							P2-Na 0.62 Mn 1/2 Fe 1/2 O
	Absorption (A.U.)						"Z"-Na 0.24 Mn 1/2 Fe 1/2 O P2-Na 0.45 Mn 1/2 Fe 1/2 O P2-Na 0.50 Mn 1/2 Fe 1/2 O

III.8: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra of the NaxMn1/2Fe1/2O2 system presented in Figure A-III.31. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

-176-Figure A-III.32: Comparison of the Mössbauer spectra recorded in the P2-based NaxMn1/2Fe1/2O2 system. Black circles: experimental and red line: calculated. "Z"-Na 0.14 Mn 1/2 Fe 1/2 O -177-As shown in Figures A-III.31 and A-III.32, all spectra exhibit a quadrupole doublet whose FWHM

Table A -

 A III.10: Developed formulas, awaited Fe n+ populations and Mössbauer parameters corresponding to the fit of the spectra of the NaxMn2/3Fe1/3O2 system presented in Figure A-III.34. The standard deviations on the isomer shift values are equal to 0.002 mm.s -1 . The population of the Fe (3+z)+ is distributed into the Fe 3+ and Fe 4+ sites by the formula: P(Fe 3+ ) = (δ(Fe 3+z )-δ(Fe 4+ )) / (δ(Fe 3+ )-δ(Fe 4+ )).

	Awaited results from electrochemistry							Mössbauer results (Distribution fit)
					Fe 3+				Fe 4+					Fe (3+z)+
	Developed formula	%Fe 3+ %Fe 4+	δ	Δ*	Γ	P	δ	Δ*	Γ	P	δ	Δ*	Γ	P	Repartition between	%Fe 3+ %Fe 4+
				(mm.s -1 )	(mm.s -1 )	(mm.s -1 )	(%)	(mm.s -1 )	(mm.s -1 )	(mm.s -1 )	(%)	(mm.s -1 )	(mm.s -1 )	(mm.s -1 )	(%)	Fe 3+ (%) Fe 4+ (%)
	Na 0.96 Mn 3+ 0.62 Mn 4+ 0.04 Fe 3+ 0 Fe 4+ 0 O 2	100	0	0.351	1.31	0.30 100										100	0
	Na 0.26 Mn 3+ 0 Mn 4+ 0.67 Fe 3+ 0.26 Fe 4+ 0.07 O 2 79	21	0.35	0.79	0.25 57 -0.05	0.47	0.25	9 0.17	0.92	0.25 34	19	15	76	24

Table B -

 B I.2. As one can see all materials exhibit very similar cell parameters and identical amon./bmon. ratios.

	(001)		Large grains	(-201)	(002) (200)	(-111) (110)	(-202)
	Intensity (A.U.)		Medium grains
			Small grains
	15	20	25	30	35		40	45	50	55	60	65
					2θ (°) Cu kα 1,2

Table B -I.5.

 B

	Material	amon. (Å)	bmon. (Å)	cmon. (Å)	βmon. (°)
	P'3-Na2/3NiO2	4.970(5)	2.862(3)	5.742(4)	105.9(1)
	P''3-Na1/2NiO2	4.919(6)	2.832(3)	5.816(7)	105.6(1)
	O''3-Na2/5NiO2	4.941(3)	2.809(2)	5.858(6)	106.52(7)

Table B -

 B I.

Pureté, morphologie et électrochimie des matériaux de départ Diffraction des rayons-X

  Depuis que l'électricité est produite puis acheminée vers les foyers et installations publiques, nous vivons plus longtemps, en meilleure santé et avons un accès direct à l'information et aux gens. Aujourd'hui, notre mode de vie nomade nécessite que l'on soit accompagné de nos appareils de communication. Pour rendre cela possible, il a fallu non seulement miniaturiser les composants électroniques constituant nos appareils mais également les doter d'une source d'énergie portable : les batteries 21 (Nickel-Cadmium, Nickel-hydrure métallique). Cependant, les besoins d'énergie croissants d'appareils toujours plus performants ont nécessité le développement d'une nouvelle technologie capable de délivrer de hautes densités d'énergie : la technologie Li-ion. Les oxydes lamellaires de formule AxMO2 (A = Li ou Na, M = métal de transition et x ≤ 1) sont des matériaux connus et étudiés pour leurs propriétés physiques depuis les années 1950 [1-9]. Devant la nécessité de développer une nouvelle technologie de batteries, beaucoup de systèmes AxMO2 ont été étudiés à nouveau, pour leurs propriétés de (dés)intercalation réversible des ions alcalins (A + ). Parmi ces études, la découverte de l'activité électrochimique de LiCoO2 en batteries Li par l'équipe de Goodenough en 1980 [10] allait se révéler marquante et la première batterie Li-ion fut commercialisée en 1991 par Sony©. Faisant suite à la découverte de Goodenough, une majeure partie des recherches se focalisèrent sur les matériaux pour batteries Li-ion, la technologie Na-ion ne pouvant tenir la comparaison pour des applications à haute densité d'énergie. En effet, le sodium possède une masse molaire plus de trois fois supérieure à celle du lithium (22,99 g.mol -1 vs. 6,941 g.mol -1 ) et est également plus volumineux (les rayons ioniques des espèces Na + est Li + sont respectivement égales à 1.02 Å et 0.76 Å), impliquant des densités d'énergies volumiques et massiques faibles pour la technologie Na-ion. De plus, le potentiel du couple redox Na + /Na, supérieur de 0,3 V à celui du lithium (E° (Na+/Na) = -2, 71 V vs. ENH 22 et E° (Li+/Li) = -3,01 V vs. ENH [11]), entraine une perte d'énergie. Depuis les années 1990, les matériaux d'électrode positive de la famille des LiMO2 ont gagné en sécurité et en complexité. De nos jours, des matériaux de type Li(Ni, Co, Les diffractogrammes de rayons-X des différentes phases sont donnés sur la Figure R.2. Les paramètres de maille et distances inter-feuillets sont donnés dans le Tableau R.1.

	10 R.1.b. Figure R.2 : Diffractogrammes de rayons-X expérimentaux et calculés pour (a) P2-Na0.77Mn2/3Fe1/3O2, (b) 20 30 40 50 60 70 80 a) P2-Na 0.77 Mn 2/3 Fe 1/3 O 2 (002) (004) (100) (101) (102) (103) (104) (006) (105) (106) (110) (112) (008) 2θ (°) Cu kα 1,2 Intensity (A.U.) 10 20 30 40 50 60 70 80 b) P2-Na 0.67 Mn 1/2 Fe 1/2 O 2 (002) (004) (100) (101) (102) (103) (104) (106) (110) (112) (008) (006) (105) 2θ (°) Cu kα 1,2 Intensity (A.U.) 10 20 30 40 50 60 70 80 d) O3-Na 0.82 Mn 1/3 Fe 2/3 O 2 (003) (104) (105) (009) (006) (102) (101) (107) (108)
	P2-Na0.67Mn1/2Fe1/2O2, (c) (O3+O'3)Na0.82Mn1/2Fe1/2O2 et (d) O3-Na0.82Mn1/3Fe2/3O2 phases. Croix rouges :
	observé, ligne noire : calculé, ligne bleue: différence et barres vertes : Bragg. (a, b, d) : affinement de type
	Rietveld et (c) : affinement de type LeBail.
	Al)O2 [12-15] et Li(Ni, Mn, Co)O2 [16, 17] équipent les nouveaux véhicules électriques. D'autres matériaux
	de structures dites « spinelle » (LiMn2O4) et « olivine » (LiFePO4) sont également de potentiels candidats
	au remplacement des LiMO2, pour des raisons de sureté accrue et de toxicité moindre [18-21].
	Cependant, le monde des années 2010 doit toujours faire faces à de nombreux problèmes
	énergétiques. Si les pays développés ont un accès quotidien à l'énergie, ce n'est pas le cas des pays

  Comme nous le détaillerons plus tard, plusieurs changements structuraux sont observés au cours de la charge. La phase intercalée présente une distorsion monoclinique et une structure O'3. La désintercalation conduit à l'apparition d'une phase de type O3 (structure du matériau de départ) à travers un domaine biphasé pour 0.85 ≤ x < 0.94. Pour x < 0.62, une phase de type P3 apparaît. Elle possède une Il est remarquable que la phase O3 ne disparaisse pas entièrement pendant la charge. A défaut de disparaître, la position des pics (00l)O3 montre une diminution importante de la distance inter-feuillet. Ce résultat inattendu est reproductible et réversible si la cellule est déchargée. Afin de vérifier si ce phénomène n'était pas induit par le mode « operando », une expérience similaire a été réalisée à l'équilibre et a montré les mêmes résultats. Indubitablement pour x < 0.62 il y a coexistence de deux systèmes qui sont désintercalés simultanément, comme nous le verrons plus tard.A partir des paramètres de maille déduits des diffractogrammes il est possible d'estimer les distances inter-feuillet. Les évolutions de ces distances ainsi que des paramètres de maille sont données

				(003) O3
		(003) P3
									After discharge back to
									1.5 V
	0.0 distance inter-feuillet supérieure à celle de la phase O3 comme le montrent les positions des pics de a) b)
	1 diffraction (003)P3 et (003)O3, ce qui s'explique par la géométrie prismatique des polyèdres NaO6 0.16 "X"
	(006) O3 (006) P3 (contrairement à la géométrie octaédrique dans la phase O3). Cette modification structurale est confirmée (101) O3 (012) O3 (104) O3 0.39 0.56 0.62 O3 par la disparition du pic (104)P3 dont l'intensité est très faible sur les diffractogrammes des phases de type x in Na x Mn 1/3 Fe 2/3 O 2 (101) P3 (012) P3 P3 P3 comparée aux phases de type O3.
									0.85
	O'3			(001) O'3	(002) O'3	(-201) O'3	(-111) O'3 (200) O'3 (110) O'3	(-202) O'3 (111) O'3	0.96	0.94
	15	16	17	18 31 32 33 34 35 36 37	40 41 42 43
					2θ (°) Cu kα 1,2		E (V)
		(003) O3	(001) O'3		(002) O'3
	O'3	a) (003) P3				(-111) O'3 (110) O'3 (200) O'3 (-201) O'3	(-202) O'3	(111) O'3	b) 0.96	0.94	0.9 1.0
					(006) O3	(101) O3	(012) O3	(104) O3	0.85	0.8
	O3 P3				(006) P3		(101) P3	(012) P3	0.62	0.39 0.56	0.3 0.4 0.5 0.6 0.7	x in Na x Mn 1/3 Fe 2/3 O 2
	"X"								0.16	0.2
									0.1
	15		16	17	18 31 32 33 34 35 36 37	40 41 42 43	4	3	2
					2θ (°) Cu kα 1,2		E (V)
							-237-

'3-Na 0.96 Mn 1/3 Fe 2/3 O 2 (

  La présence simultanée de phases présentant des empilements O3 et P3 lors de la désintercalation électrochimique est difficile à envisager. Afin de l'expliquer, nous pouvons supposer des fluctuations de compositions dans le matériau initial, indétectables par diffraction des rayons-X. Ces fluctuations peuvent être dues à (i) la coexistence de particules avec des rapports Mn / Fe légèrement différents ou (ii) la coexistence de particules avec et sans lacunes de Mn. La littérature montre que la stabilité relative des empilements O3 et P3 est directement corrélée à la covalence des liaisons dans les feuillets MO2 et au taux d'intercalation[36]. Suivant cette hypothèse, une partie de la phase O3 serait désintercalée à via un mécanisme de type solution solide pendant que l'autre serait transformée en P3. Il est impossible de conclure sur ce point sans réaliser davantage d'expériences. Afin d'étudier la réversibilité des différentes transitions structurelles la cellule in situ a été à nouveau déchargée à 1.5 V et un diffractrogramme de rayons-X a été enregistré sous potentiel constant et avec les mêmes paramètres d'acquisition que pour l'expérience in situ. Les diffractogrammes collectés après la première et seconde décharge sont comparés Figure R.11. Etonnamment, la distorsion monoclinique n'est pas observée après la seconde décharge. Ceci est expliqué par le plus faible taux d'intercalation atteint après la seconde décharge (x ≈ 0.8). La fraction d'ions Mn 3+ ne représente plus que 13 % des ions M n+ ce qui est insuffisant pour induire un effet Jahn-Teller coopératif. La grande différence entre les taux d'intercalation atteints après la première et la seconde décharge implique que le matériau Diffractogrammes de rayons-X enregistrés in situ pendant une étape potentiostatique (1.5 V) après les (a) première et (b) seconde décharges de l'expérience sur le système NaxMn1/3Fe2/3O2.

	2 a subit des transitions structurelles irréversibles pendant la charge, qui peuvent être dues à nos conditions P3* + O3* 2/3 O de cyclage. La migration du fer dans l'espace inter-feuillet, déjà considérée pour NaxFeO2 [35] est une 1/3 Fe explication envisageable. O3* appears P3 + O3 30 31 32 33 34 35 36 37 38 39 40 41 42 43
		a) First discharge to 1.5 V -OC2/m)
		(002)
	Intensity (A.U.)	(-201) b) Second discharge to 1.5 V -O3-Na ≈0.8 Mn 1/3 Fe 2/3 O 2 (R-3m) (-111) (200) (110) (101) (012) (006)	(-202)	(111) (104)
	Figure R.11 : 30 31 32 33 34 35 36 37 38 39 40 41 42 43 2θ (°) Cu kα 1,2
		-242--243-

Etude des mécanismes Redox pendant la désintercalation électrochimique

  La courbe galvanostatique de O3-Na0.77Mn1/3Fe2/3O2 (Figure R.4d) montre un saut de potentiel marqué à x ≈ 2/3, ce qui correspond au taux de fer dans le matériau et donne une première idée des domaines d'activité des couples redox Fe 4+ /Fe 3+ (haut potentiel, x < 2/3) et Mn 4+ /Mn 3+ (bas potentiel, x > 2/3). Afin de confirmer ces attributions, deux techniques spectroscopiques ont été utilisés in situ pendant la désintercalation électrochimique : la spectroscopie d'absorption des rayons-X et la spectroscopie Mössbauer du57 Fe.

	Operando in situ X-ray Absorption Near Edge Spectroscopy (XANES)
	Les limites de temps imposées par l'utilisation d'une ligne synchrotron 23 nous ont conduits à
	mener l'expérience in situ (operando). L'évolution des spectres XANES enregistrés aux seuils K du fer et du
	manganèse pour le système de type O3-NaxMn1/3Fe2/3O2 est donnée sur la Figure R.12.
	a) Mn K-edge
	Absorption (a.u.)			x=0.93 x=0.80 x=0.68 x=0.60 x=0.41							x=0.93 x=0.80 x=0.68 x=0.60 x=0.41
	6535	6540	6545	6550	6555	6560	6565	6570	7110	7115	7120	7125	7130	7135	7140	7145
				Energy (eV)
	Figure R.12. Spectres XANES enregistrés aux seuils K du Mn et de Fe in situ (operando) pendant la charge
	d'une cellule NaxMn1-yFeyO2//Na. La cellule a été préalablement déchargée.
	Dans le domaine 2/3 ≤ x < 1, un décalage important du maximum d'absorption au seuil K du
	manganèse vers de plus hautes énergies est observé. Ce décalage est associé à la réaction redox Mn 3+ →
	Mn 4+ comme l'a confirmé la comparaison avec les composés de référence. Dans le même domaine de
	composition aucun décalage notable du maximum d'absorption au seuil K du fer n'est observé. Ainsi, seul
	le couple Mn 4+ /Mn 3+ est impliqué à bas potentiel.
	Pour x < 0.67, aucun décalage notable du maximum d'absorption au seuil K du manganèse n'est
	observé. Simultanément, un léger décalage du maximum d'absorption au seuil K du fer vers les énergies
	plus élevées est observé. Des références que nous avions préparées (O3-NaFeO2 et Na0.55FeO2) ont montré
	la même tendance lorsque le degré d'oxydation du fer augmente. Il est ainsi fortement suggéré que le
	procédé redox Fe 3+ → Fe 4+ soit impliqué à haut potentiel. La spectroscopie Mössbauer a donc été utilisée
	pour confirmer cette attribution.

23

En collaboration avec l'équipe du Pr. Hwang, NTUST/NSRRC, Taiwan, R.O.C. Beamline (NSRRC): 17C.

  Nous avons ensuite réalisé l'étude in situ. Les spectres des phases NaxMn1/3Fe2/3O2 ont été enregistrés pour des valeurs d'intercalation sélectionnées : x = 0.96, 0.85, 0.67, 0.58 et 0.38. Ces spectres ont été enregistrés pendant la charge de la cellule faisant suite à une décharge préalable. Les spectres enregistrés à potentiel constant sont donnés Figure R.13b. Comme nous pouvons le voir, il n'y a pas de décalage dans la position des pics dans le domaine 0.96 ≥ x ≥ 0.67. Au contraire, un décalage significatif vers les vitesses les plus basses est observé pour les spectres correspondant aux compositions x = 0.58 et x = 0.38. Ce décalage indique une évolution de l'état d'oxydation des ions Fe 3+ . Comme pour le spectre du matériau initial, tous les spectres enregistrés in situ se présentent sous la forme d'un doublet quadripolaire dont l'asymétrie et la largeur à mi-hauteur augmentent lors de la désintercalation électrochimique.Un premier affinement de type Lorentzien a été réalisé afin de déterminer le nombre de sites présents pour chaque composition (Tableau R.3). Dans le domaine 0.67 ≤ x < 1, deux sites Fe 3+ (δ ≈ 0.34 -0.37 mm.s -1 ) sont nécessaires pour décrire les spectres. Les déplacements isomériques associés n'évoluant pas de façon notable dans le domaine 0.67 ≤ x < 1 confirment que les ions Fe 3+ ne participent pas au processus redox à bas potentiel et que seuls les ions Mn 3+ sont oxydés. Pour x < 0.67, on observe l'apparition des sites Fe 4+ (δ ≈ 0 mm.s -1 ) et Fe (3+z)+ (δ ≈ 0.10 -0.18 mm.s -1 ) ce qui confirme l'oxydation des ions Fe 3+ à haut potentiel. .s -1 et 0.71 mm.s -1 pour les sites Fe 3+ (1) et Fe 3+ (2) respectivement). La plus haute valeur de l'éclatement quadripolaire pour le site Fe 3+ (1) indique qu'il est davantage affecté par l'effet Jahn-Teller coopératif des ions Mn 3+ environnants. De plus, quand la structure évolue vers un empilement de type O3 (x = 0.85 puis x = 0.67), la valeur de l'éclatement quadripolaire du site Fe 3+ (1) diminue continuellement alors que l'éclatement quadripolaire du site Fe 3+ (2) reste constant. Nous pouvons donc conclure que le site Fe 3+ (1) correspond à des ions Fe 3+ principalement entourés d'ions Mn n+ (incluant une distribution d'environnements) alors que le site Fe 3+ (2) correspond à des ions Fe 3+ principalement entourés d'autres ions Fe 3+ . Les populations des deux sites donnent un rapport Fe 3+ (1) : Fe 3+ (2) égal à 40 : 60 qui est maintenu dans le domaine 0.96 ≥ x ≥ 0.67. Dans ce même domaine, les déplacements isomériques diminuent suivant la désintercalation électrochimique, ce qui est en accord avec l'augmentation de l'état d'oxydation moyen des ions Mn n+ environnants.Dans le domaine x < 0.67, tous les ions Mn 3+ ont été oxydés, d'après les mesures d'absorption des rayons-X, et le procédé redox actif est maintenant Fe 3+ → Fe 4+ . Trois sites sont maintenant nécessaires pour pouvoir décrire les spectres. Le premier site est caractérisé par un déplacement isomérique égal à 0.336 -0.321 mm.s -1 et correspond à des ions Fe 3+ à haut spin en environnement octaédrique. Le deuxième site montre un déplacement isomérique proche de 0 mm.s -1 , caractéristique d'ions Fe 4+ en environnement octaédrique. L'ion Fe 4+ a déjà été observé dans des oxydes lamellaires aux états haut-spin[START_REF] Prado | [END_REF] et bas spin[122, 123]. L'état de spin du Fe 4+ dans notre matériau n'a, en revanche, pas encore été déterminé. Si l'existence ces ions Fe 3+ et Fe 4+ était prévisible, la présence d'un troisième site d'état d'oxydation intermédiaire Fe (3+z)+ l'était moins. Ce troisième site possède un déplacement isomérique de valeur intermédiaire entre celles des sites Fe 3+ et Fe 4+ . Une origine possible de cet état d'oxydation moyen est l'existence d'un mécanisme de « Fast Electron Hopping » entre les espèces Fe 3+ et Fe 4+ , comme cela a déjà été observé dans les systèmes LixNi0.70Fe0.15Co0.15O2[START_REF] Prado | [END_REF] et Ni1-yFeyOOHx / Ni1-yFey(OH)2, ex situ[122] et in situ[123]. La population du site Fe (3+z)+ peut être répartie entre les espèces Fe 3+ et Fe 4+ si l'on considère la somme des populations Fe 3+ et Fe 4+ égale à 1. Cette répartition est donnée dans le Tableau R.3.

	éclatements quadripolaires des deux sites correspondant à la phase O'3 (x = 0.96) sont différents (Δ* =
	Site Fe 3+ (A) Fe 3+ (B) Absorption (A.U.) Un important élargissement des pics est observé au cours de la désintercalation de x = 0.96 à x = δ (mm.s -1 ) FWHM (mm.s -1 ) Δ (mm.s -1 ) P (%) 0.353 0.30 0.88 25 0.354 0.35 0.58 75 -4 -3 -2 -1 0 1 2 3 4 -4 -3 -2 -1 0 1 2 3 4 Velocity (mm.s -1 ) Na 0.96 Mn 1/3 Fe 2/3 O 2 Na 0.85 Mn 1/3 Fe 2/3 O 2 Na 0.67 Mn 1/3 Fe 2/3 O 2 Na 0.58 Mn 1/3 Fe 2/3 O 2 Na 0.38 Mn 1/3 Fe 2/3 O 2 Na 0.77 Mn 1/3 Fe 2/3 O 2 (pristine material) a) b) 0.38 ce qui est en accord avec l'apparition de nouveaux sites Fe n+ . Cela suggère également une augmentation du désordre dans le matériau au cours de la désintercalation. Afin de prendre en compte ce phénomène nous avons réalisé un second type d'affinement, dit en distribution, se basant sur des valeurs de déplacement isomériques fixées d'après les affinements Lorentziens. Les largeurs à mi-hauteur ont été fixées à 0.20 mm.s -1 (x = 0.96 et x = 0.85), 0.25 mm.s -1 (x = 0.67) et 0.30 mm.s -1 (x = 0.58 et x = 0.38) afin de prendre en compte l'augmentation du désordre dans le matériau au cours de la désintercalation. Grâce à ces affinements en distribution, nous avons pu déterminer l'éclatement quadripolaire moyen (Δ*) et la population des différents sites. Ces résultats sont donnés dans le Tableau R.3 avec les formules développées des matériaux et les populations attendues pour les différents sites. 1.00 mmOn peut observer une bonne concordance entre les compositions déduites des spectres Les résultats peuvent être séparés en deux groupes selon le procédé redox actif : Mn 3+ → Mn 4+ (x Mössbauer (Na0.58Mn1/3Fe2/3O2 et Na0.40Mn1/3Fe2/3O2) et celles déduites de l'électrochimie ≥ 2/3) et Fe 3+ → Fe 4+ (x < 2/3). Les spectres correspondant aux compositions x = 0.96, 0.85 et 0.67 sont (Na0.58Mn1/3Fe2/3O2 et Na0.38Mn1/3Fe2/3O2, respectivement). Parallèlement, l'éclatement quadripolaire similaires et peuvent être affinés en utilisant deux sites Fe 3+ , comme pour le matériau initial. Ces sites sont appelés Fe 3+ (1) et Fe 3+ (2) afin d'éviter toute confusion avec les sites déduits de l'affinement Lorentzien. moyen augmente lors de la désintercalation, notamment pour le site Fe 4+ (Δ* = 0.19 mm.s -1 et 0.55 mm.s -
	Les signaux associés à ces sites correspondent à des doublets quadripolaires qui montrent des
	déplacements isomériques similaires (δ = 0.355 mm.s -1 et 0.365 mm.s -1 pour la composition x = 0.96). Les
	-245--246-

. NaNiO2 et le diagramme de phases de NaxNiO2 (1/3 ≤ x ≤ 1) R.2.a. Contexte de l'étude

  1-y Fe y O 2 Comme l'on peut le voir l'évolution des rapports entre les paramètres de maille est linéaire pour nous résultats expérimentaux. De plus, l'empilement (O'3 ou P'2) ne semble pas avoir d'impact sur la distorsion à la vue des rapports amon./bmon. (O'3) et borth./aorth. (P'2) qui sont égaux (1.84) pour les deux polytypes Na≈1Mn1/2Fe1/2O2. Afin de vérifier cette hypothèse, nous avons également étudié l'évolution des En 2013, Vassiliaras et al. ont publié une étude concernant la cyclabilité sur le long terme de O'3-NaNiO2 [34]. Malgré une capacité de première charge égale à 150 mAh.g -1 pour des batteries Na cyclées entre 1,25 et 3,75 V, la réversibilité du matériau est grandement limitée par la formation d'une phase intermédiaire au cours de la première décharge, qui empêche la réversibilité vers O'3-NaNiO2. Cette phase intermédiaire ainsi que les différentes transitions de phases furent observées in situ par Han et al. en 2014 [134].

	système NaxMn2/3Fe1/3O2 (0.1 ≤ x ≤ 0.74). L'augmentation du rapport Mn : Fe prévient ici l'apparition de la phase peu cristallisée, notée « Z », jusqu'à 4.3 V pour le système NaxMn2/3Fe1/3O2. Dans les phases de type P2 et O3, la formation des phases « X » et « Z » en charge se produit via R.2Les premières recherches portant sur O'3-NaNiO2 datent de 1954 et sont attribuées à Dyer et
	Intermediate phases la création de fautes d'empilement. Dans les systèmes de type O3 les fautes d'empilement sont "X" al [2]. Depuis, O'3-NaNiO2 a principalement été étudié pour ses propriétés magnétiques [43, 124-132], distances M-O (polyèdres MO6) sur la Figure R.16 : simultanément créées dans les phases O3 et P3. Ces fautes sont hypothétiquement l'apparition de plans physiques [133] et structurales [2, 43]. 2.45 d'octaèdres NaO6 dans la phase P3 ou l'apparition de plans O1 dans la phase O3. Dans les systèmes de type P2, la phase dite « Z » se forme également via l'apparition de plans d'octaèdres NaO6 dans la phase 2.40 La première étude montrant la possibilité de désintercaler réversiblement les ions sodium de O'3-
	Intermediate phases NaNiO2 fut menée par Braconnier et al. en 1982 [38]. Cette étude révèle que la (dés)intercalation Intermediate phases Intermediate 2.35 P2. phases Influence du rapport Mn : Fe sur l'état intercalé Comme nous l'avons discuté avec la Figure R.14, l'effet Jahn-Teller coopératif des ions Mn 3+ 2.05 2.10 2.15 2.20 2.25 2.30 électrochimique se produit suivant une succession de mécanismes biphasés entre plusieurs composés M-O distances (Å) définis : P'3-Na0.91NiO2, P''3-Na0.84NiO2, O''3-Na0.81NiO2 and O'''3-Na0.79NiO2.
	2.00
	1.95
	1.90
	O'3-Na 0.96 Mn 1/3 Fe 2/3 O 2	O'3-Na 0.95 Mn 1/2 Fe 1/2 O 2	P'2-Na ≈1 Mn 1/2 Fe 1/2 O 2	P'2-Na 0.96 Mn 2/3 Fe 1/3 O 2	O'3-NaMnO 2
	Figure R.16 : Evolution des distances M-O des octaèdres MO6 dans les phases P'2 et O'3-Na≈1Mn1-yFeyO2.
	O'3-NaMnO2 : données provenant de [44].
	La Figure R.16 confirme bien que la distorsion des octaèdres MO6 est identique pour les phases
	O'3-Na≈1Mn1/2Fe1/2O2 (distances M-O égales à 4 x 1.99 Å et 2 x 2.19 Å) et P'2-Na≈1Mn1/2Fe1/2O2 (distances
	M-O égales à 4 x 1.99 Å et 2 x 2.18 Å). On observe également que les octaèdres MO6 sont davantage
	distordus lorsque la quantité d'ions Mn 3+ augmente (distances M-O égales à 4 x 2.02 Å et 2 x 2.14 Å pour
	O'3-Na Na≈1Mn1/3Fe2/3O2 vs. 4 x 1.94 Å et 2 x 2.39 Å pour O'3-NaMnO2).
	Figure R.15 : Evolution des rapports amon./bmon. (phases O'3) et borth./aorth. (phases P'2) en fonction du
	rapport Mn : Fe. O3-NaFeO2 : données provenant de [35]. O'3-NaMnO2 : données provenant de [44].
		-249--250--251-

conduit à l'apparition d'une phase distordue (O'3 ou P'2) pour les plus hauts taux d'intercalation. De plus, augmenter le rapport Mn : Fe conduit à l'observation de ces phases distordues sur un domaine en composition plus étendu. Afin d'étudier l'évolution de l'effet Jahn-Teller coopératif avec le rapport Mn : Fe, nous avons tout d'abord étudié l'évolution des rapports amon./bmon. (phases O'3) et borth./aorth. (phases P'2). Cette évolution est donnée Figure R.15. Afin d'en faciliter l'interprétation, nous avons considéré tous les ions Mn n+ au degré d'oxydation +III. Nos travaux sur le système NaxNiO2 firent suite à ceux de Vassiliaras et al., notre but étant d'étudier le diagramme de phases de NaxNiO2 par diffraction des rayons-X in situ. Par comparaison avec d'autres systèmes NaxMO2 étudiés à l'ICMCB et dans la littérature, nous nous attendions à observer des ordres sodium -lacunes pour les différents composés définis [48, 55, 56, 64]. Les premiers travaux de synthèse et de caractérisation sur ce système furent réalisés par T. Phraewphiphat au cours de deux stages doctoraux réalisés à l'ICMCB en 2013 et 2014.

R.

2.b. Synthèse de O'3-NaNiO2 dit « moyens grains »

	O'3-NaNiO 2 Space group : C2/m
	a mon. = 5.3087(7) Å, b mon. = 2.8453(3) Å, c mon. = 5.5695(7) Å, β mon. = 110.41(1)°a mon. /b mon. = 1.87
	Atom	Wyckoff		Coordinates		Occupancy	ADP (Ų)
	Na	2c	0	0	1/2	0.99(3)	0.6(4)
	Ni	2b	0	1/2	0	1	0.8(3)
	O	4i	0.224(2)	0	0.192(2)	1	0.5(5)
	Ni-O distances		4 * 1.93(1) Å		2 * 2.11(1) Å
	Rwp = 12.51%; R B = 4.09%
	Tableau R.4 : Paramètres structuraux et facteurs de mérite calculés à partir du diffractogramme de O'3-O'3-NaNiO2 a été préparé suivant le mode opératoire décrit par Braconnier et al. [38]. Ce protocole consiste à mélanger et broyer les oxydes Na2O et NiO (préparé par décomposition thermique de Ni(NO3)2 NaNiO2 (moyens grains).
	.6 H2O) dans un mortier sous atmosphère inerte. Le mélange est ensuite placé dans une nacelle en or, Le diffractogramme obtenu est correctement indexé dans le groupe d'espace C2/m des structures
	introduite dans un four tubulaire et chauffée à 650°C pendant 15h sous oxygène. Le matériau est ensuite de type O'3. Les paramètres de maille sont similaires à la littérature et donnent un rapport amon./bmon. égal
	trempé à l'air et directement placé sous vide avant d'être introduit en boite à gants. La différence majeure à 1,87 qui est dû à l'effet Jahn-Teller coopératif des ions Ni 3+ . Cet effet est confirmé par l'existence de deux
	avec les conditions de synthèse décrites par Braconnier et al. [38] est le non-ajout d'excès de sodium au liaisons longues (2 x 2.11 Å) et de quatre liaisons courtes (4 x 1.93 Å) dans les octaèdres NiO6 (Tableau
	cours de la synthèse, qui avait pour effet d'augmenter la taille des grains et d'introduire des limites de R.4).
	diffusion ionique dans le matériau. Les pics de diffraction sont bien définis impliquant un matériau bien cristallisé. Ceci a été confirmé
	par microscopie électronique à balayage (insert de la Figure R.17) qui fait état d'une taille de cristallites
	comprise entre 250 et 650 nm.
				-253-

La pureté de O'3-NaNiO2 ainsi obtenu a été confirmé par diffraction des rayons-X (Figure R.17).

-252-Figure R.17 : diffractogrammes observés et calculés (affinement de type Rietveld) de la phase O'3-NaNiO2 (moyens grains). Croix rouges : observé, ligne noire : calculé, ligne bleue : différence et traits verticaux verts : réflexions. Insert : cliché MEB du même échantillon.

  a été étudié in situ lors de la charge d'une batterie NaxNiO2//Na. L'expérience s'est déroulée en mode GITT afin de pouvoir mieux caractériser de probables phases ordonnées. Les diffractogrammes de rayons-X issus de l'expérience sont donnés sur la Figure R.20. Dans la littérature, la phase Na≈0.80NiO2 n'a été observée in situ qu'en décharge[134], certainement à cause du mode operando choisi par les auteurs.Les distances inter-feuillet déduites de la position des pics de diffraction (001)mon. sont données Figure

	de la désintercalation. R.22.
							3.2
		4.2
		4.0					3.1
		3.8					3.0
		3.6
	E (V)	3.2 3.4					2.9	0.50 0.55 0.60 0.65 0.70
		3.0			1/3
						2/5
		2.8					1/2	0.55
		2.6								2/3
		2.4
		0.0	0.1	0.2	0.3	0.4	0.5		0.6	0.7	0.8	0.9	1.0
						x in Na x NiO 2
	Les diffractogrammes correspondant aux composés définis (x = 1 ; ≈ 0,8 ; 2/3 ; 1/2 ; 2/5 et 1/3 (fin de
	l'expérience)) sont tracés en rouge. Par rapport à la littérature un nouveau domaine monophasé est
	observé pour x ≈ 0.80. Par la suite nous nous réfèrerons à la phase correspondante en tant que
							-255-

« Na≈0.80NiO2 ». Son existence est mise en évidence sur les zooms des pics de diffraction (001)mon. présentés sur la Figure R.21, et qui permettent de suivre l'évolution de ces mêmes pics pour chaque phase au cours Figure R.20 : Evolution des diffractogrammes de rayons-X enregistré in situ pendant la charge d'une batterie NaxNiO2 (moyens grains) / NaPF6 in PC (1M) + 2 wt% FEC / Na. Les diffractogrammes représentés en rouge correspondent aux composés définis.

  Les flèches noires mettent en évidence la présence de pics de diffraction supplémentaires.Dans les oxydes lamellaires NaxMO2, un tel phénomène est généralement associé à l'existence d'ordres Na + / lacunes entre les feuillets MO2[48,55,56,64]. Inclure ces pics de diffraction supplémentaires dans un affinement de type LeBail nécessite la détermination de nouveaux paramètres de maille pour la sur-maille, le plus souvent se basant sur ceux de la sous-maille. La sur-maille et la sousmaille ne partagent pas toujours la même symétrie ni le même groupe d'espace.

		Entre les diffractogrammes #18 (x = 1/2) et #20, la désintercalation à partir de la phase P''3-
	Na1/2NiO2 est le phénomène prédominant et la distance inter-feuillet augmente. Entre les
	diffractogrammes #20 et #21, les deux phénomènes se compensent et aucun déplacement du pic (001)mon.
	n'est observé. L'élargissement du pic (001)mon. visible sur le diffractogramme #21 implique l'augmentation
	du nombre de fautes d'empilement. Ce phénomène prédomine jusqu'au diffractogramme #22, entrainant
	une diminution de la distance inter-feuillet. La coexistence des feuillets d'octaèdres et de prismes NaO6
	est à l'origine de l'élargissement du pic (001)mon. dans le domaine 2/5 < x < 1/2. Pour x ≤ 2/5
	(diffractogramme #22), tous les ions sodium sont dans une coordination octaédrique et la distance inter-
	feuillet augmente de façon continue jusqu'à x = 1/3, confirmant le mécanisme de type « solution solide ».
		Si l'on regarde de plus près les diffractogrammes correspondant aux phases définies dans le
	domaine 17 -30 °, on peut observer l'apparition réversible de pics de diffraction supplémentaires. Cette
	observation est facilitée sur la Figure R.24.
	Na + deintercalation	increases Interslab (IS) Interslab (IS) increases IS decreases Constant IS					x = 1/2 (P''3) x = 2/5 (O''3)	18 22 20 24	XRPD number
								16
		15.4	15.6	15.8	16.0	16.2	16.4	16.6
					2θ (°) Cu kα 1
	Figure R.24 : Diffractogrammes correspondant aux composés définis observés pour x = 1, 0.8, 2/3, 1/2,
	2/5 et 1/3.
					-259-

  Comme il est rappelé sur la Figure R.26, le diagramme de diffraction de la phase Na≈0.8NiO2 ne montre aucun pic de diffraction supplémentaire dans le domaine 15 -35 ° (2θ Cu kα1). Cependant, plusieurs pics de diffraction dont l'origine semble être une séparation de pics existants de la symétrie monoclinique sont observés. Une symétrie triclinique est donc attendue pour la phase Na≈0.8NiO2.

	Material	Space Group	asup. (Å)		Supercell parameters bsup. (Å) csup. (Å)		βsup. (°)	asub./bsub.
	P'3-Na2/3NiO2	P21/a	4.9715(4) = asub.	8.589(1) = 3 x bsub.	5.7391(5) = csub.		105.84(1) = βsub.	1.74
	¤ (-202) (111) Tableau R.5 : Paramètres de maille et groupes d'espaces des super-mailles des composés définis P'3-(002) P''3-Na1/2NiO2 P21/m 4.918(1) = asub. 5.6633(7) = 2 x bsub. 5.8155(8) = csub. 105.52(1) 1.74 = βsub. (-201) (110) (200) (-111) O''3-Na2/5NiO2 C2/m 4.941(3) = asub. 14.046(8) = 5 x bsub. 5.856(5) = csub. 106.53(8) = βsub. 1.76 (003) (201) Na2/3NiO2, P'3-Na1/2NiO2 et O'3-Na2/5NiO2. Les relations entre les paramètres des sur-mailles et des sous-(-112) mailles sont indiquées en gras.
	La phase Na≈0.8NiO2
					(002) Na ≈0.8 NiO 2	(-201) (110)	(200)	(-111)	(-202) (111) ¤	(201)	(-112)	(003)
	30			35				40					45
		(100)	(-111)	(040)	(041) 2θ (°) Cu kα 1 (002) O'3-NaNiO 2	(-201)	(110)	(200)	(-111)	(-202)	(111) ¤	(201) (-112)	(003)
			(-201) (002)		(200) (110)	(-111)		(-202)
	30			35				40					45
					2θ (°) Cu kα 1
						-262-

Malheureusement, toute tentative d'indexation de ce diffractogramme a échoué, en partie à cause de l'élargissement des pics de diffraction. Une indexation basée sur les paramètres de maille monocliniques reportés dans

[134]

n'a également pas donné de résultats plus satisfaisants. Figure R.26 : Comparaison des diffractogrammes enregistrés lors de l'expérience in situ pour les composés définis (haut) Na≈0.8NiO2 et (bas) O'3-NaNiO2. Les échelles d'intensité des deux diffractogrammes ne sont pas identiques.

  et O3 NaxMn1-yFeyO2 sont sorties. Si les résultats de ces études portant sur les phases de type P2 sont en accord avec nos travaux, nos matériaux de type O3 se sont révélés différents. Cela est probablement dû à (i) un taux de sodium inférieur dans nos matériaux par rapport à la littérature (x = 0.77 vs. 1.0) et/ou (ii) à la plus haute température de synthèse employée.Les caractérisations électrochimiques menées sur les matériaux du système NaxMn1-yFeyO2 ont montré que tous étaient capables de (dés)intercaler réversiblement les ions Na + entre 1.5 et 3.8 -4.3 V. appuyée par des mesures de spectroscopie Mössbauer du57 Fe qui ont montré un désordre croissant dans les phases les plus désintercalées.De même, les matériaux de type P2 possèdent une structure distordue pour les états les plus intercalés. La désintercalation électrochimique est rapidement accompagnée par l'apparition d'une phase P2 observée sur un vaste domaine en composition. Une désintercalation plus poussée (jusqu'à 4.3 V) conduit à l'apparition d'une nouvelle phase peu cristallisée dont l'origine et la structure sont incertaines.Les expériences de diffraction des rayons-X menées in situ permettent d'optimiser les conditions de cyclage pour chaque matériau. Concernant de futures applications, la prochaine étape serait l'optimisation des rapports Mn : Fe dans les phases P2 ainsi que la substitution partielle par d'autres métaux de transition (Al, Ni, Co,…). Cette approche a déjà été envisagée dans la littérature.La seconde partie de ce manuscrit concerne la phase O'3-NaNiO2 et le diagramme de phase NaxNiO2. En jouant sur l'ajout -ou non-d'un excès de sodium et sur la température de synthèse, nous avons pu obtenir des échantillons avec différentes tailles de cristallites (« gros », « moyen » et « petits »).

	La désintercalation est accompagnée par les procédés redox suivants : Mn 3+ → Mn 4+ (bas
	potentiel) et Fe 3+ → Fe 4+ (haut potentiel). Parmi les matériaux de composition NaxMn1/2Fe1/2O2, la
	transition entre les procédés redox semble être distincte pour la phase de type P2, tandis que les ions Fe 3+
	et Mn 3+ pourraient être oxydés simultanément pour un domaine restreint pour la phase de type O3.
	Au cours du cyclage, les systèmes NaxMn1-yFeyO2 subissent plusieurs transitions structurales,
	comme l'ont montré des expériences de diffraction des rayons-X menées in situ pendant la charge. Tous
	les matériaux présentent une structure distordue à bas potentiel (1.5 V) / haut taux d'intercalation, induite transition entre les phases P'3-Na1/2NiO2 et O'3-Na2/5NiO2 avec la formation d'une phase de structure
	par l'effet Jahn-Teller coopératif des ions Mn 3+ . Lors de la charge, les matériaux de type O3 subissent intermédiaire P'3/O'3. Les diffractogrammes des composés définis x = 2/3, 1/2, 2/5 et 1/3 ont montré des
	plusieurs transitions (O'3 → O3 → P3 → « X ») dont les domaines d'observations sont dépendants du pics de sur-structures, caractéristiques d'ordres longue distance sodium / lacunes. Ces structures ont été
	rapport Mn : Fe. A la fin de la charge (4.3 V), l'apparition d'une phase de faible cristallinité, notée « X », a davantage étudiées grâce à des mesures de diffraction de rayons-X synchrotron menées à l'ESRF. Cette
	été observée et reliée à la perte de capacité induite par des cyclages à haut potentiel. Davantage de étude est complétée par les travaux de Dr. S. Kumara Swamy (DFT et RMN du 23 Na).
	mesures seront nécessaires pour étudier l'origine de cette phase désintercalée qui pourrait se trouver
	dans la création de fautes d'empilements dans les espaces inter-feuillets. Cette hypothèse est davantage
	-264-

Les matériaux de type P2 se sont montrés les plus performants en terme de capacité, de rétention de capacité et de conductivité ionique. Pour les matériaux de types P2 et O3, accroître le rapport Mn : Fe permet de modifier l'électrochimie. Dans les matériaux de type O3, un plus haut taux de Mn permet d'accroître la rétention de capacité. Dans les matériaux de type P2 un plus haut taux de Mn permet d'accroître la capacité en décharge mais également de cycler le matériau à un plus haut régime. L'électrochimie de ces matériaux s'est révélée différente dans le domaine 2/3 ≤ x ≤ 1 et la diffraction des rayons-X menée in situ a révélé que trois phases étaient impliquées : O'3-NaNiO2, Na≈0.8NiO2 et P'3-Na2/3NiO2. De par la taille importante des cristallites dans la phase dite « gros grains » (0.50 -1.50 µm), les trois phases sont observées simultanément alors que seules deux phases le sont dans les échantillons dits « moyens grains » et « petits grains ». Une symétrie triclinique est attendue pour la phase Na≈0.8NiO2. Cependant, l'élargissement important des pics de diffraction empêche toute indexation du diffractogramme de rayons-X. L'étude par diffraction des rayons-X menée in situ sur l'échantillon dit « moyens grains » a confirmé les transitions entre plusieurs composés définis de structures P'3 et O'3 reportés par Braconnier et al. en 1982. Ces transitions P'3 ↔ O'3 sont facilitées car elles n'impliquent que des glissements des feuillets MO2. Cependant l'étude in situ a montré des mécanismes complexes, notamment lors de la

Table of Figures / Tables Chapter I: The Na x MO 2 layered oxides and the Na-ion battery technology

 of

Table I . 1 :

 I1 Usual space groups and atomic positions for the O3, P3 and P2 structure types. Projections of the distorted structures in the (amon.,cmon.) and (amon.,bmon.) planes (O'3, P'3) or in the (borth.,corth.) and (aorth.,borth.) ones (P'2).

	Figure I.4: Representation of the ground electronic states and lift of degeneracy of 3d orbitals for the (a)
	HS 3d 4 and (c) LS 3d 7 configuration states. A schematic representation of the corresponding MO6 octahedra
	is also given (b).
	Figure I.5:

Table I . 2 :

 I2 Usual space groups and atomic positions for the P'2, P'3 and O'3 distorted structure types.

Table I . 3 :

 I3 Relations between the hexagonal cell parameters and the orthorhombic (P2 / P'2 structures) or monoclinic (O3 / O'3 and P3 / P'3) ones for a non-distorted example.

Table I . 6 :

 I6 Electrochemical properties of different NaxMO2 materials. All voltages ranges are expressed versus the Na + /Na redox couple. TableI.7a: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple. TableI.7b: Electrochemical performances of different NaxMO2 with mixed compositions on the M site. All voltages ranges are expressed versus the Na + /Na redox couple.

	Chapter II: Experimental techniques
	-266-

Table II . 1 :

 II1 Experimental conditions concerning the XRPD and Synchrotron XRPD experiments carried out in this work.

SHE: Standard Hydrogen Electrode

Due to the sodium content of the starting P2 materials, the capacity retention is compared to the 2 nd cycle.

Due to the sodium content of the starting P2 materials, the capacity retention is compared to the 2 nd cycle.

Rwp = 9.50%; R B = 7.55% (with excluded regions)

In collaboration with Pr. Hwang's research team, NTUST/NSRRC, Taiwan, R.O.C. Beamline (NSRRC): 17C.

In collaboration with Dr. M. Suchomel, Argonne Photon Source, Argonne National Laboratory, IL, USA. Beamline: 11BM.

* 2.33(2) Å 2 * 2.40(1) Å Rwp = 14.36 %; R B = 9.37 % with excluded regions (graphite)

Contrairement au terme « battery » en anglais, le mot « batterie » implique un système réversible et donc rechargeable, contrairement aux piles, qui ne le sont pas.

pour x = 0.58 et x = 0.38, respectivement). Cela indique une fois de plus une augmentation du désordre dans le matériau lors de la désintercalation, et corrobore les résultats obtenus par diffraction des rayons-X qui montraient la coexistence de deux phases : P3 (majoritaire) et O3 (minoritaire).

Acknowledgments

Remerciements

MO2 layers and different polytypes for sodium layered oxides NaxMO2 are possible, depending on the Na/M ratio, the synthesis temperature and the nature of the transition metal(s). These polytypes show different oxygen layers stacking sequences, and are easily described using a denomination specific to layered oxides [36]. It consists in a letter corresponding to the alkali geometric site (Octahedral of Prismatic) followed by the number of MO2 layers needed to describe the structure in the hexagonal cell. A representation of the three possible structure types (O3, P3 and P2) is given in Figure I.3. -24-Figure I.3: Representation of the O3, P3 and P3 structure types. The Na + environment in the different

Les phases ordonnées P'3-Na2/3NiO2, P''3-Na1/2NiO2 et O''3-Na2/5NiO2

Afin d'étudier les structures des phases P'3-Na2/3NiO2, P''3-Na1/2NiO2 et O''3-Na2/5NiO2, nous avons conduit des mesures de diffraction des rayons-X synchrotron haute résolution à l'ESRF 24 (Figure R.25). La type d'empilement des différentes phases est déterminée par les intensités relatives des pics de diffraction (111)mon. et (-202)mon. par rapport aux pics (201)mon. et (-112)mon. dans la sous-maille. Les diffractogrammes associés aux phases de type O'3 montrent des pics de diffraction (111)mon. et (-202)mon. très intenses par rapport aux pics (201)mon. et (-112)mon.. Le phénomène inverse est observé sur les diffractogrammes des phases P'3. Ainsi les diffractogrammes présentés Figure R.25 nous permettent bien de confirmer les structures des phases P'2-Na2/3NiO2, P''3-Na1/2NiO2 et O''3-Na2/5NiO2. Le meilleur rapport signal / bruit obtenu grâce aux mesures synchrotron permettent une meilleure distinction des pics de sur-structure que nous avons essayé d'inclure dans une sur-maille. Pour cela, nous avons d'abord indexé la sous-maille en utilisant une symétrie monoclinique (C2/m). Plusieurs sur-mailles dont les paramètres étaient multiples de ceux de la sous-maille ont ensuite été considérées pour inclure les pics de sur-structure dans la symétrie P-1. Une fois les meilleurs paramètres de maille identifiés (i.e. les paramètres les plus petits permettant d'inclure tous les pics de diffraction de la sur-structure), nous avons identifié les groupes d'espaces possibles en se basant sur les conditions de réflexion et en considérant une symétrie monoclinique. Pour chaque matériau, un seul groupe d'espace est possible. Les résultats des affinements de profils de type LeBail pour les super-mailles sont montrés sur la Figure R.25. Les groupes d'espaces et paramètres de maille des super-mailles sont reportés dans le Tableau R.5. Les relations entre les paramètres des sous-mailles et des sur-mailles y sont également données.

Chapter II: Experimental techniques

Table of contents A-II.1.c. In situ XRPD study during Na deintercalation

To follow the structural changes that the material undergoes during Na + deintercalation, we carried out an operando in situ XRPD study during the charge of a NaxMn1/3Fe2/3O2//Na battery. Data were collected during the first charge following a preliminary discharge of the cell that lead to the Na0.96Mn1/3Fe2/3O2 composition as the starting point. In order to be close to the fully intercalated phase, the galvanostatic discharge was followed by a potentiostatic intercalation at 1.5 V until the current was close to 0 mA. After recording the pattern of the electrode material at 1.5 V, the battery was charged at C/80. The acquisition conditions were optimized to record an XRPD pattern every 0.013 Na + / formula unit: the selected angular ranges were 13-20° and 30-43°, the step size 0.02° and the acquisition time ≈ 4s / step.

Selected parts of the resulting XRPD patterns are shown in

Ex situ 57 Fe Mössbauer spectroscopy study of the NaxMn1/2Fe1/2O2 system

No Mössbauer spectrum was recorder for the pristine material as it involves two different phases (mixture of O3 and O'3). Several compositions were prepared by the potentiostatic route on pellets consisting of Carbon Black and Active Material. The targeted compositions were x = 0.95 (E = 1.5 V, ≈ 100 % Mn 3+ , O'3 structure), x = 0.67 (E = 2.56 V, O3 structure), x = 0.55 (middle of the voltage jump (E = 2.97 V), ≈ 100 % Mn 4+ ), x = 0.44 (E = 3.7 V) and x = 0.22 (E = 4.0 V). The spectra corresponding to these compositions are shown in Figure A-II. 29 and are compared altogether in Figure A-II.30. All spectra exhibit a quadrupole doublet. As for the study carried out on the NaxMn1/3Fe2/3O2 system, the spectra can be separated into two groups depending if Fe 3+ ions are involved or not in the oxidation processes. The preliminary fit using a Lorentzian profile shows that Fe 3+ ions are not involved in the redox process for 0.5 ≤ x < 1.0 ( Figures A-II.29a-c) and are partially oxidized for x < 0. 55 (Figures A-II.29d-e).

The spectrum of the almost fully intercalated phase (Figure A-II.29a) exhibits a higher FWHM than the spectra recorded for x = 0.67 and x = 0.55. This is a consequence of the reduction of the Mn 4+ ions, which induce the cooperative Jahn-Teller effect responsible of the monoclinic distortion in O'3-Na0.95Mn1/2Fe1/2O2.

The spectra recorded for the x = 0.44 and x = 0.22 materials exhibit an increasing broadening upon deintercalation. An increasing dissymmetry is also observed on the low-velocity side of the spectra, induced by the appearance of Fe 4+ ions. These two phenomenons indicate an increase of the disorder in the material, in agreement with the operando in situ XRPD experiment (increasing number of stacking faults to form the "X" phase and presence of an intermediate phase).

All spectra were fitted by a Lorentzian of distribution fit. In the Mn 3+ → Mn 4+ activity range, the spectra corresponding to the x = 0.95, 0.67 and 0.55 composition require two sites to be fitted. The associated isomeric shifts are comprised between 0.338 and 0.345 mm.s -1 and therefore correspond to Fe 3+ ions in an octahedral FeO6 environment. These sites are labeled Fe 3+ (A) and Fe 3+ (B) in Table A-II.9. If the quadrupole splitting values associated to the two sites are quite similar from x = 0.95 to x = 0.55 (ΔFe3+(A) = 0.86 -0.96 mm.s -1 and ΔFe3+(B) = 0.62-0.64 mm.s -1 ), the FWHM values are higher for the x = 0.95 material (ΓFe3+(A) = 0.37 mm.s -1 and ΓFe3+(B) = 0.33 mm.s -1 ) than for the x = 0.67 and x = 0.55 ones (ΓFe3+(A) ≈ 0.32 mm.s - 1 and ΓFe3+(B) ≈ 0.28 mm.s -1 ). As previously explained this broadening is the consequence of the cooperative Jahn-Teller effect induced by the important amount of Mn 3+ ions (≈ 45 % of the total transition metal ions amount).

The spectra recorded when the Fe 3+ → Fe 4+ redox process is involved, for x = 0.44 and 0.22, exhibit an increasing FWHM, implying an increase of the disorder. The spectra were fitted by a Lorentzian fit (x =

A-II.4. Conclusion on the O3-based NaxMn1-yFeyO2 systems

In this chapter were further investigated the electrochemical and structural properties of the O3based NaxMn1-yFeyO2 materials.

As mentioned in Chapter A-I, the O3-based systems exhibit worst electrochemical properties than the P2-based systems (poorer conductivity, inferior discharge capacity…). However, the electrochemical properties can be improved by increasing the Mn / Fe ratio from 1/2 to 1/1. This increase allows maintaining good discharge capacity in the 1.5 -4.0 V range as 91 % of the second cycle discharge capacity are still reached for the NaxMn1/2Fe1/2O2 system vs. 74 % for the NaxMn1/3Fe2/3O2 one, after 29 cycles.

In situ XRPD during the charge of Na-cells showed that the O3-based materials undergo a series of structural transitions: O'3 → O3 → P3 → "X" from the fully intercalated state to the deintercalated ones (up to 4.3 V). However, several residual phases of unknown origin are observed simultaneously to the O3 and P3 domains. We suggested that these residual phases could result from (i) the coexistence of particles with slightly different Mn / Fe ratios or (ii) the existence of particles with or without Mn vacancies.

Thanks to X-ray absorption spectroscopy and Mössbauer spectroscopy, we confirmed that the Mn 3+ → Mn 4+ redox process is active at low voltage and that the Fe 3+ → Fe 4+ one is active at high voltage, upon Na + deintercalation.

A-III.2.c. In situ studies of the NaxMn2/3Fe1/3O2 phase diagram

The structural behavior of the material upon cycling was studied by in situ XRPD: first during the full charge of the battery, from 1.5 V to 4.3 V in operando mode, and then upon discharge from the pristine material, in the GITT mode.

Operando in situ study during the Na deintercalation

The experimental conditions of the operando in situ experiment were optimized in order to record XRPD patterns in the 13 -20° and 30 -43° 2θ ranges every 0.01 Na + per formula unit. The evolution of the XRPD patterns along with the complete charge of the battery is shown in The experiment starts from the intercalated state of the material whose corresponding formula is Na0.96Mn2/3Fe1/3O2. This phase can be indexed in the orthorhombic system (Cmcm space group, P'2 structure). The orthorhombic distortion is clearly emphasized by the splitting of the (102)P2 diffraction line into the (022)P'2 and (112)P'2 ones. The P'2-NaxMn2/3Fe1/3O2 structure is observed alone for a narrow Na range: 0.94 < x ≤ 0.96.

For x ≤ 0.94, a new set of diffraction lines appears at 16.3° and 38.1 °. These diffraction peaks correspond to the (002)P'2 and (022)P'2 reflections of a newly formed P'2 phase. To differentiate the two P'2 phases, they will be referred to as the "fully-intercalated P'2f phase" and as the "intermediate P'2i phase". The biphasic domain between the two P'2 phases is observed for 0.76 < x ≤ 0.96. Then, the intermediate P'2i phase is observed alone in a very short range: 0.74 ≤ x ≤ 0.76.

A-III.2.d. Ex situ X-ray powder diffraction study of P'2-Na0.96Mn2/3Fe1/3O2

A sample of the intercalated P'2 phase was prepared by the potentiostatic method. Once recovered and washed, the powder was analyzed by XRPD. The experimental and calculated (Rietveld Due to the limitations of laboratory XRPD (signal/noise ratio, Fe fluorescence under the Cu kα radiation…), it was not possible to refine as many atomic parameters as synchrotron XRPD data allows to.

Therefore we fixed the sodium content to 0.96 from the electrochemical curve, and we fixed reasonable ADP values for the Na, Mn, Fe and O atoms (1.0, 0.5, 0.5 and 0.8 Ų, respectively).

Nonetheless, the XRPD pattern of the intercalated P'2 phase is successfully indexed in the orthorhombic symmetry (Cmcm space group). The borth./aorth. ratio is equal to 1.88 and shows that the cooperative Jahn Teller distortion is higher than in the P2-Na≈1Mn1/2Fe1/2O2 phase (borth./aorth. = 1.84). The cooperative Jahn Teller effect is confirmed by the distortion of the MO6 octahedra which exhibits 4 short M-O distances (2.01(1) Å) and 2 long ones (2.25(2) Å).

As observed in the P'2-Na≈1Mn1/2Fe1/2O2 phase, only the Nae site which shares edges with the surrounding MO6 octahedron is occupied in order to minimize the Na + -Na + repulsions.

A-III.4. Conclusion on the P2-based NaxMn1-yFeyO2 systems

In this chapter were further investigated the electrochemical and structural properties of the P2based NaxMn1-yFeyO2 materials.

As mentioned in Chapter A-I, the P2-based systems exhibit the best electrochemical properties among the P2/O3 based NaxMn1-yFeyO2 systems. Batteries cycled in the 1.5 -4.0 V range showed interesting second discharge capacities of 140 mAh.g -1 (P2-based NaxMn1/2Fe1/2O2 system) and 152 mAh.g - 1 (P2-based NaxMn2/3Fe1/3O2 system). The associated capacity retentions at the 50 th cycle showed interesting values of 85 % (P2-based NaxMn1/2Fe1/2O2 system) and 82 % (P2-based NaxMn2/3Fe1/3O2 system).

In situ XRPD during the charge of Na-cells showed that the P2-based materials undergo three structural transitions: P'2 → P2 → "Z" from the fully intercalated state to the deintercalated ones (up to 4.3 V). Contrarily to the O3-based materials, no residual phases were observed.

Thanks to X-ray absorption spectroscopy and Mössbauer spectroscopy, we showed that the Mn 3+ → Mn 4+ redox process is active at low voltage and that the Fe 3+ → Fe 4+ one is active at high voltage, upon Na + deintercalation. The same observation was made concerning the O3-based systems. -186-This last chapter on the NaxMn1-yFeyO2 (y = 1/3, 1/2 and 2/3) presents a discussion on the impact of the Mn / Fe ratio on the O3 and P2 materials, based on the results presented in chapters A-I to A-III.

Chapter A-IV: Influence of the Mn / Fe ratio on the electrochemical and structural properties

Table of contents

The evolution of the electrochemical properties is investigated first and then the evolution of the structural properties is discussed.

A-IV.1. Effect on the electrochemical properties

In Chapter A-I, we already studied the impact of the Mn content on the discharge capacities of the NaxMn1-yFeyO2 materials, when cycled between 1.5 and 3.8 V in Na cells. The conclusions of this study are reminded below:

(1) In P2 materials, increasing the Mn content leads to better second discharge capacities.

(2) In O3 materials, increasing the Mn content decreases the second discharge capacity but leads to better capacity retention.

(3) The comparison between the P2 and O3 NaxMn1/2Fe1/2O2 materials shows that the P2 material exhibit higher discharge capacity and better capacity retention.

In Chapters A-II and A-III, we investigated the impact of the upper cut-off voltage on the galvanostatic curves of the different materials. We now compare these results for different Mn / Fe ratios, first on the O3 systems and then on the P2 systems. The main influence of the higher Mn / Fe ratio (from 1 / 2 to 1 / 1) is to delay the sudden voltage jump associated to the change of active redox couple. Furthermore, one can see that increasing the Mn / Fe ratio allows deintercalating more Na + ions when the cut-off voltage is increased from 4.0 V to 4.3 V (+ 0.02 Na + ions per formula unit in the O3-based NaxMn1/3Fe2/3O2 system vs. +0.14 Na + ions per formula unit in the O3-based NaxMn1/2Fe1/2O2 one). This leads to higher discharge capacities when cycling the O3-based NaxMn1/3Fe2/3O2 material up to 4.0 or 4.3 V compared to the cycling in the 1.5 -3.8 V range, as evidenced in Figure A-IV.2. The higher Mn / Fe ratio also induce the second voltage plateau to occur at higher voltage (≈ 4.0 V vs. ≈ 3.9 V for O3-based NaxMn1/3Fe2/3O2). As a consequence, the capacity retention of the batteries cycled in the 1.5 -4.0 V is higher for the O3-based NaxMn1/2Fe1/2O2 system (91 % after 29 cycles) than for the NaxMn1/3Fe2/3O2 one (74 % after 29 cycles).

A-IV.1.a. Impact on the O3 systems

Concerning the P2-type materials, increasing the Mn / Fe ratio from 1 / 1 to 2 / 1 leads to the observation of the P'2 phase(s) on a wider x range. A second P'2 domain is also observed for the NaxMn2/3Fe1/3O2 system and delays the apparition of the P2-type phase (x = 74 vs. x = 0.95 in the NaxMn1/2Fe1/2O2 system). Because of that, the P2-type phase is observed on a wider domain in the NaxMn1/2Fe1/2O2 system (0.26 ≤ x ≤ 0.95) than in the NaxMn2/3Fe1/3O2 one (0.1 ≤ x ≤ 0.74). Contrarily to the O3 based materials, increasing the Mn content prevent the appearance of a pure "Z" phase up to 4.3 V for the P2 based NaxMn2/3Fe1/3O2 system while it appears at x = 0.25 in the P2-based NaxMn1/2Fe1/2O2 one.

In both systems the formation of the "X" or "Z" phases in charge is achieved through the apparition of stacking faults. In the O3-based systems stacking faults are occurring simultaneously for the P3 and O3 phases and presumably consist in the appearance of octahedral surroundings for some NaO6 ions from the P3 phase or in the appearance of O1 planes among the O3 phase. In the P2-based materials, the "Z" phase also appears through the apparition of stacking faults (NaO6 octahedra planes) in the P2 phase.

As both "X" and "Z" phases show octahedral surroundings of the Na + ions and appear for comparable sodium contents (0.16 ≤ x ≤ 0.25), one can expect them to show similar interlayer distance.

This is confirmed in

B-I.1. O'3-NaNiO2 in the literature

The first synthesis of O'3-NaNiO2 by solid state reaction of Na2O and NiO is attributed to Dyer et al. in 1954 [2]. O'3-NaNiO2 (monoclinic) was mostly studied for its magnetic [43,[124][125][126][127][128][129][130][131][132] and physical [133] properties or for its reversible transition towards O3-NaNiO2 (rhombohedric) for T > 220°C [2,43].

The electrochemical properties of O'3-NaNiO2 as a positive electrode in a Na battery were only studied in 1982 by Braconnier et al. [38] who highlighted the existence of several ordered phases within border of biphasic domains: P'3-Na0.91NiO2, P''3-Na0.84NiO2, O''3-Na0.81NiO2 and O'''3-Na0.79NiO2. In 2013, Vassiliaras et al. reported a study on the cyclability of O'3-NaNiO2 [34]. Despite the interesting initial charge capacity of ≈ 150 mAh.g -1 when cycled between 1.25 and 3.75 V, the reversibility is limited by the formation of an intermediate phase in discharge that seems to prevent the formation of the original O'3-NaNiO2 phase. Therefore, the subsequent discharge capacity decreases to 120 mAh.g -1 . The different structural transitions and the formation of the intermediate phase in discharge were observed in situ by Han et al. in 2014 who confirmed the existence of peculiar compositions, separated by biphasic domains [134].

Following the work of Vassiliaras and her collaborators' [34], we decided to reinvestigate the NaxNiO2 phase diagram by in situ XRPD during the charge of a corresponding battery. Several sodium / vacancy orderings were expected, by comparison to other NaxMO2 systems studied at the ICMCB and in the literature [48,55,56,64,135]. The synthesis and optimization of the materials as well as the first electrochemical characterizations were carried out by T. Phraewphiphat during two Ph.D. training periods in our laboratory.

B-I.2. Synthesis of the O'3-NaNiO2 pristine materials

Several synthesis routes are reported for the synthesis of O'3-NaNiO2 such as classic solid state [2,34,38,43,124,125,127,128,131,133,134], molten hydroxide method [129,130] or single crystal growth [132]. In the present work, we followed the protocol described by Braconnier et al. [38] in 1982, as the synthesis duration (less than 24 hours) allows us to prepare the material rapidly and to obtain it in powderform, which is more adapted for electrochemical cycling. The protocol consists in mixing and grinding Na2O and NiO (prepared from Ni(NO3)2 .6 H2O) altogether in a mortar under Ar atmosphere. 10 wt% excess of Na are added in order to compensate the high volatility of Na oxides. The mixture is then placed into a gold boat introduced in a furnace and heated at 650 °C during 15 hours under O2 atmosphere (heating ramp: +2 °C.min -1 ). After the heat treatment, the gold boat is quenched under air and directly placed under vacuum before entering the glovebox (Ar atmosphere).

Then, we tried several synthesis conditions by varying the excess Na amount and the duration of the heat treatment. After XRPD characterization of the resulting materials, three of them were selected.

The corresponding conditions are resumed in

B-I.5.b. Influence of particle size on the deintercalation processes

Consecutively to the GITT study in the 2/3 ≤ x ≤ 1 range for the large, medium and small grain sized materials, we carried out the same experiment in situ, recording a XRPD pattern at the end of each relaxation period. The sodium step was originally 0.025 Na + ions per formula unit. However some parasitic current due to the electrochemical cell slightly shifted the galvanostatic curves. 13 the "large grains" and "medium grains" samples show a pure O'3-NaNiO2 phase in the pristine material. On the other hand, the "small grains" sample exhibits a small portion of Na≈0.8NiO2 in the starting material which is the origin of the extra diffraction peak observed on the XRPD pattern recorded after the synthesis (Figure B-I.2). Upon slight Na + deintercalation (x ≈ 0.97), the O'3-NaNiO2 and the Na≈0.8NiO2 phases are observed simultaneously for all materials. Further deintercalation leads to the apparition of the P'3-Na2/3NiO2 phase in the "large grains" samples and the three phases are observed simultaneously down to x ≈ 0.7. Then, for x = 2/3, only the P'3-Na2/3NiO2 phase and a small part of the O'3-NaNiO2 phase are observed. We note that there is no variation of the interslab distances for any of the three phases in the 2/3 ≤ x ≤ 0.945 range for the "large grains" sample.

The behavior of the "medium grains" and "small grains" samples is identical to the one described during the full charge of the battery on the "medium grains" material: the O'3-NaNiO2 and Na≈0.8NiO2 phases are observed for the higher sodium contents (0.835 ≤ x < 0.96 and 0.835 ≤ x ≤ 1.0 for the "medium grains" and "small grains" samples respectively). While no variation of interslab distance of the O'3-NaNiO2 phase is observed, the Na≈0.8NiO2 phase shows a progressive increase of its interslab parameter typical of a solid solution (Figure B-I.14). The solid solution behavior of the Na≈0.8NiO2 phase is observed alone in a narrow range (0.80 ≤ x < 0.835) for both samples. Further deintercalation leads to the appearance of the P'3-Na2/3NiO2 phase which exhibits a constant interslab distance while the one of the Na≈0.8NiO2 phase continuously increases. For x = 2/3, only the P'3-Na2/3NiO2 phase is observed for the "medium grains" and "small grains" samples.

General Conclusion and perspective work

The present work is a study of the structural and electrochemical properties of NaxMn1-yFeyO2 and NaxNiO2 materials as positive electrodes for Na-ion batteries.

The first part concerned the preparation by a self-combustion type synthesis of four materials in the NaxMn1-yFeyO2 system: the P2-Na0.66Mn0.66Mn1/3Fe2/3O2, P2-Na0.62Mn1/2Fe1/2O2, (O3+O'3)-Na0.77Mn1/2Fe1/2O2 and O3-Na0.77Mn1/3Fe2/3O2 ones. Experimentally, we showed that a high Mn / Fe ratio stabilizes P2 structures while a low Mn / Fe ratio stabilizes O3 ones. In parallel to this thesis, several studies were released on P2 and O3-NaxMn1-yFeyO2 materials. If the P2 phases are similar to the one we obtained, our O3-type materials are definitely different, probably because of (i) the lower initial Na content (x = 0.77) compared to the literature (x = 1.0) and/or (ii) the higher synthesis temperature.

The electrochemical characterizations carried out on the NaxMn1-yFeyO2 materials showed that all materials are capable of reversibly (de)intercalate Na + ions in Na cells in the 1.5 -3.8 V, 1.5 -4.0 V and 1.5 -4.3 V ranges. Among our materials, the most interesting electrochemical properties were obtained for the P2 materials which show higher discharge capacities and capacity retentions. The lower polarizations observed on the galvanostatic curves of the P2 materials imply a higher ionic conductivity and explain why they can handle cycling at higher rate values. For both O3 and P2 materials increasing the Mn / Fe ratio has a tremendous effect on the electrochemical properties. Concerning O3 materials, it increases the capacity retention on the long-term cycling of the batteries. Among P2 phases, increasing the Mn content slightly increases the available discharge capacity but also allows cycling at higher rate values.

The sodium deintercalation process is accompanied by the Mn 3+ → Mn 4+ (low voltage region) and Fe 3+ → Fe 4+ (high voltage region) redox processes. Among the NaxMn1/2Fe1/2O2 systems, the transition from a redox process to another seems to occur distinctively in the P2 material while both Mn 3+ and Fe 3+ ions could be oxidized in a short range in the O3 one.

Upon cycling, all systems undergo several structural transitions that were investigated by in situ X-ray powder diffraction during Na deintercalation from the fully intercalated state and up to 4.3 V. The results highlighted the cooperative Jahn-Teller effect of the Mn 3+ ions for the most intercalated states.

Upon deintercalation, the O3-type systems go through several phase transitions (O'3 → O3 → P3 → "X") whose existence domain is strongly correlated to the Mn / Fe ratio. At the end of the charge the apparition of a poorly ordered phase, noted "X", was evidenced and is correlated to the capacity loss observed when cycling at high voltage. Further experiments are required to investigate the origin of the deintercalated phase which could be explained by stacking defaults between the layers (altering of NaO6 prisms and octahedrons). This hypothesis is reinforced by the 57 Fe Mössbauer spectroscopy experiments which highlighted an important disorder in the materials for low Na contents.

Similarly, the P2-type systems show an orthorhombic distortion for the most intercalated states of both systems. Na + deintercalation from x ≈ 1 quickly lead to the apparition of the P2 phase which is observed on a wide sodium content range. Further deintercalation lead to the observation of a poorly ordered phase for the most deintercalated states of the materials. The origin and structure of this new phase are still uncertain. The in situ X-ray powder diffraction results allow us to optimize the voltage range, based on the stability domain of the different materials. Concerning potential applications, the next step would be the optimization of the Mn : Fe ratio in P2 phases and the partial substitution by other transition metals such as Al, Ni, Co… as it was already started in the literature.

The second part of this work reports the preparation of O'3-NaNiO2 materials of very reasonable purity by solid state synthesis. By adding -or not-an excess sodium amount and varying the synthesis temperature, we were able to prepare O'3-NaNiO2 with different grain sizes, labelling the corresponding samples as "large grains", "medium grains" and "small grains". The electrochemical study of these samples revealed different behaviors in the 2/3 ≤ x ≤ 1 range and in situ XRPD carried out during the relaxation of corresponding batteries revealed the existence of three phases: O'3-NaNiO2 (the pristine one), "Na≈0.8NiO2" and P'3-Na2/3NiO2. Due to the important particle size (0.50 -1.50 µm) in the "large grain sample", all three phases are observed simultaneously while only two phases are observed at the same time in the "medium grains" and "small grains samples". The "Na≈0.8NiO2" phase is characterized by a splitting of the monoclinic diffraction peaks of the pristine material suggesting a triclinic symmetry. The important broadening of the peaks prevented any description of the structure from the XRPD patterns.

The in situ XRPD carried out during the relaxation of a battery assembled from the "medium grains" samples in the 1/3 ≤ x ≤ 1 range confirmed the phase transitions between several O'3 and P'3 structures first mentioned by Braconnier et al. in 1982 [38]. These transitions are facilitated as they only require MO2 slabs gliding. The in situ study revealed a complex behavior, especially between the P'3-Na1/2NiO2 and the O'3-Na2/5NiO2 phases with the formation of an O'3/P'3 intermediate phase. The XRPD patterns of the x = 2/3, 1/2, 2/5 and 1/3 peculiar compositions show extra-diffraction lines, which are characteristic of long-range Na/vacancy orderings. Due to the few number of peaks available the study of the Na/vacancy orderings is difficult to carry out on laboratory XRPD patterns. For that purpose, synchrotron XRPD patterns were recorded at the ESRF to facilitate the resolution of the structures of P'3-Na2/3NiO2, P'3-Na1/2NiO2 and O'3-Na2/5NiO2. This work is completed by DFT and 23 Na NMR studies carried out by Dr. S Kumara Swamy at ICMCB.

Résumé étendu

Table des matières

R.1. Le(s) système(s) NaxMnyFe1-yO2 R.1.a. Synthèse des matériaux

Les matériaux NaxMn1-yFeyO2 ont été synthétisés par une voie de type auto-combustion qui consiste en une réaction redox entre une (des) espèce(s) oxydante(s) (généralement des nitrates de métaux de transition ou d'alcalins) et un combustible tel que la glycine qui joue également le rôle d'agent complexant [START_REF] Djurdjevic | Transition Met[END_REF].Ce type de synthèse est caractérisée par la très haute température de flamme rapidement atteinte, généralement supérieure à 1000°C [109], et par l'obtention d'un précurseur de petite taille et / ou peu cristallisé [111]. Nous justifions l'utilisation de cette voie de synthèse par notre volonté d'obtenir des précurseurs avec une bonne distribution entre les espèces fer et manganèse.

Suivant le protocole présenté ci-dessus, nous avons préparé les matériaux NaxMn1-yFeyO2 en dissolvant des nitrates de manganèse, fer et sodium (Alfa Aesar Mn(NO3)2.4H2O (97% pureté), Fe(NO3)3.9H2O (98%) and NaNO3 (99%) respectivement) dans de l'eau distillée. Un excès massique de 10 % de NaNO3 a été ajouté afin de prendre en compte la volatilité du sodium lors du traitement thermique à suivre. Après dissolution totale des nitrates, de la glycine est ajoutée selon un rapport nitrate / glycine égal à 8 / 1. Le large excès de nitrate permet de diminuer la température et la violence de la réaction. La Les diffractogrammes de rayons-X montrent des phases pures et bien cristallisées. Les affinements des structures (LeBail ou Rietveld) conduisent à des paramètres de maille proches de la littérature [26].

Comme attendu des différents empilements, les phases P2 ont une distance inter-feuillet supérieure à celle des phases O3. Cela est dû à la grande taille des sites prismatiques NaO6.