Pauline Fey

Valeri Parravic

Daniela Bănaru

Re Dierking

Benoit Galzin

Tarik Lebreton

Nicholas V C Meziane

Mayalen Polunin

Yves Zubia

Letourneur

Multi-trophic markers illuminate the understanding of the functioning of a remote, low coral cover Marquesan coral reef food web


Diego Urbina Salazar

Emmanuelle Vaudour

Nicolas Baghdadi

Eric Ceschia

Dominique Arrouays

Combined use of Sentinel-2 images and Sentinel-1-derived moisture maps for soil organic carbon content mapping in croplands, South-western France

diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.


Baharak Pentecôte
email: baharak.pentecote@gmail.com

Vanina Mollo

Irène Gaillard

Intervening in a social crisis context. How to create the conditions for a dialogue about work?

A social crisis context added to financial difficulties

, including: negative financial results leading to the lay-off of the previous director and the arrival of a new one; disagreements between the new director and the medical team (physicians and midwives) on several strategic decisions leading to strikes, and the resignation of several doctors and of two presidents of the Hospital Medical Committee. All these elements contributed to a climate of distrust and feelings of insecurity among the staff, which led to a breakdown in dialogue between the director and the medical practitioners, which progressively extended to the entire staff, leading to organizational malfunctions (such as a department's shut down) and a deterioration of the social climate.

Understanding the determinants of the crisis

. Based on the ergonomic analysis of work, our objective was to understand the origins of social tensions and create the conditions to bring real work at the centre of debates and decisions. Our approach is part of a systemic and holistic vision that studies the reciprocal influences between organization and activity and develops participatory and reflective methodologies aimed at Intervening in a social crisis context. How to create the conditions for a dialogue about work?

supporting a continuous process of interactions in management practices [START_REF] Gaillard | Organisation du travail[END_REF]. In this paper, we will describe the main actions and regulations carried out by ergonomists to bring work to the heart of the concerns of governance and social dialogue, in this social crisis context that has strongly impacted our own maneuverability.

The questionnaire as a means to bring work into discussions

3.1. An ergonomic pre-diagnosis rejected without any chance to dialogue An initial pre-diagnosis phase, based on a documentary study, open observations and 38 interviews with all the stakeholders of the institution, made it possible to build a history of the social crisis, and highlighted a deleterious management style of the director, specifically characterized by a lack of listening and dialogue with the employees, as well as strong differences with regard to the criteria for the quality of work [START_REF] Clot | Le prix du travail bien fait[END_REF] and the actions to be undertaken to improve the financial situation.

The pre-diagnosis was strongly rejected by our client who, calling our neutrality into question, showed a kind of mistrust towards us. The results were considered illegitimate, since they were based on "subjective" data, and we did not have the opportunity to compare our respective analyses in a constructive exchange. We then measured how much the opposition practices we were facing were modeled on existing forms of relationships in the institution. The expression of divergent points of view about work was not allowed, leading either to organizational silence [START_REF] Morrison | Organizational Silence: a barrier to change and development in a pluralistic world[END_REF][START_REF] Rocha | Work debate spaces: a tool for developing a participatory safety management[END_REF][START_REF] Rocha | Contributions and conditions of the structured debates on work on safety construction[END_REF] or to conflicting relational modes. We too experienced this social crisis that impacted the course of our intervention.

An organization for dialogue about work: setting up a space for dialogue and conducting a

questionnaire on working conditions While we were planning to develop a diagnosis based on the analysis of employees' activities, we had to adapt our methodology to maintain the link with our client, who was considering stopping our work. On the one hand, the setting up of a joint Steering COmmittee (SCO) representing all hospital actors, which was responsible for the methodology and the follow-up of the approach, enabled us to maintain an equidistant relationship with all the stakeholders. It constituted of an experimental discussion space governed by operating rules that the ergonomists didn't hesitate to remind of, when necessary, namely: no one holds the truth; understanding listening (without interrupting or judging); one has the right to disagree (the clarification and discussion of differences is encouraged); we are responsible for what we say and what we don't say. Although the first exchanges were very aggressive, a form of constructive conflict [START_REF] Follett | Creative experience[END_REF][START_REF] Mollo | Cultiver la diversité pour développer l'agentivité. Le rôle de la réflexivité dans la démarche ergonomique[END_REF] gradually emerged, with each member having the opportunity to express himself or herself freely and to debate with the others to overcome disagreements and develop a common response to the issues raised whenever possible. On the other hand, we designed a questionnaire to allow employees to express their views on their working conditions anonymously, and to generate statistical data that would guarantee the balanced representation of the results and preserve our neutrality. Developed by ergonomists Intervening in a social crisis context. How to create the conditions for a dialogue about work? based on existing surveys (Saphora Job of the CCECQA 1 and SUMER of the DARES 2 ), the questionnaire was discussed, adjusted, completed, and validated collectively within the SCO.

The questionnaire included 82 questions distributed in 9 headings: "Work Organization and Content", "Social Relations", "Professional Development and Employment", "Local Management", "Acknowledgement", "Salary", "Top Management and bodies of the Hospital", "Human Values", "Global Satisfaction". Following our pre-diagnosis, we also included questions directly related to the hospital. Our open observations showed poor hygiene and security conditions as well as a lack of adapted workplace and equipment. We thus wanted to confirm these matters with the questionnaire. We also wanted to question the employees about whether they felt they worked in a peaceful and trusting climate. This is because our pre-diagnosis had revealed a climate of distrust and confusion. Besides, we wanted to learn about employees' perceptions of the hospital's future and of their own future in the hospital. As the pre-diagnosis had brought the deleterious management of the director to light, we decided to duplicate the questions about local management with the same questions related to top management. For example, one of the questions under the "Local Management" heading concerned the manager's behavior with his staff. The same question was repeated in the "Top Management and bodies of the Hospital" heading regarding the director's behavior with the hospital staff. As some of the members of the hospital's board had expressed some suspicion about the staff's knowledge of the financial situation of the hospital, we needed to check this statement and we also included a question regarding the staff's perception of the board's strategy and decision-making. The questionnaire was distributed among the staff for a 33-day period.

The 57% response rate ensured the reliability of the results, which confirmed our pre-diagnosis. In particular, the management style of the director emerged very significantly as a source of dissatisfaction due to the lack of listening and consideration (65% of the respondents), the lack of recognition and involvement (54%), and the lack of information and communication (64%) [START_REF] Pentecôte | Intervenir en situation de crise sociale : des ajustements nécessaires pour amener le travail au coeur des discussions. Actes du 56ème Congrès de la SELF, Vulnérabilités et risques émergents : penser et agir ensemble pour transformer durablement[END_REF]. Unlike what was assumed by some of the board members, 62% of the employees were aware of the financial difficulties of the hospital and 76% were worried about the hospital's future. Despite some minor opposition, this diagnosis was received by our client as a necessary call to action and an opportunity to reflect upon the actions to be taken to overcome the social crisis. The questionnaire was thus the tipping point for our action, on two levels. On the one hand, the conditions of dialogue created to build it (parity and based on operating rules) enabled the different members of the SCO to experience and observe that a constructive dialogue was possible. On the other hand, we took advantage of this new perspective of our client to initiate a dialogue based on the results of the questionnaire between the different actors of the institution.

Organizing the questionnaire feedback to experiment with spaces for dialogue about work within the institution

Beyond the SCO, the dialogue about work was extended within the hospital by the organization of feedback sessions. Representatives of our client were invited as observers, but our deepest intention was to create the conditions for them to hear what the employees had to say about their work and the conditions of its realization in the hospital. Each session took place in two stages: first, a presentation of the results of the questionnaire by the ergonomists, then a collective discussion. 14 feedback sessions were first organized for all the staff, targeting an interdepartmental dialogue after the presentation of the global results of the questionnaire. In a second step, 12 feedback sessions were organized within each department where the global and the department's results were presented, which allowed the employees to compare their department's results with the global of the hospital. We set up a framework for exchange to bring the real work and the conditions of its realization into the heart of the discussions, had never been possible until then. We wanted to highlight the links between work organization and managerial practices on the one hand, and the activity, the employees' health, and the quality of care on the other, by mentioning concrete work situations. We never limited the discussion time to allow everyone (employees and the client's representatives) to feel comfortable enough to say what they wanted to say.

For many of our client's representatives, these feedback sessions were an opportunity to physically come to the hospital for the first time, which was quite symbolic and showed the desire to go to the places where the work was being done. Employees, for their part, appreciated the fact that governance representatives came to them, as some of them, who had been working for the hospital for more than 10 years, had never met a single person from governance until then. Moreover, these sessions enabled our client's representatives to hear the point of view of field employees and to engage in a dialogue with them, which had never happened before. They made it possible to make the work relatable and understandable.

Participation in several inter-and intra-departmental sessions brought our client to the realization that his assumptions were far from the realities of the work and helped him understand that the social crisis was in fact a crisis of work, which was crystallizing in the concrete conditions of the activity. The representatives were thus able to measure the impact of certain decisions, actions or behaviors on activity and social relations, as well as the commitment and need for accomplishment of employees who were just looking for doing high quality work.

In the maternity department, a midwife reported that in a room where a patient was in labor, the needed equipment was malfunctioning. She knew that her colleagues were very occupied and didn't want to disturb them. She thus had to look for a functioning equipment elsewhere in the department, leaving the patient alone for a while. She reported that accompanying the patients is part of her work and that she felt that she didn't do a good job because of the missing equipment. By allowing those of the members who were present at the feedback sessions to understand the importance of taking care of real work in managerial practices, we also rebuilt trust with our client, with whom we were able to establish a constructive dialogue.

At the end of the feedback sessions, a summary of the priority areas for improvement, both in general and by was presented, discussed, and validated by the SCO and then given to our client, with the recommendation to implement 3 rapid actions per department to improve working conditions. It was indeed urgent to send signals to the employees showing that they had been heard.

4.

A necessary first step in bringing work into discussion, to be continued… When starting this research-intervention, our objective was to produce an inventory of the situation in the institution based on the analysis of work and activity and identify the determinants of the social crisis. This initial work was meant to lead to the sharing and discussion of the results by creating spaces for debate [START_REF] Rocha | Du silence organisationnel au débat structuré sur le travail : les effets sur la sécurité et l'organisation[END_REF] within each department and then, in a transversal way, between departments. Through a participatory and systemic approach, our objective was to achieve a shared diagnosis and the co-construction of action plans that would allow for the development of activity and staff health, as well as the quality and safety of care. Our ambition was also to support the implementation of work management through action training to emphasize a processual and dynamic vision of the organization [START_REF] De Terssac | Autonomie dans le travail[END_REF][START_REF] Weick | Making sense of the organization[END_REF][START_REF] Cordelier | L'organisation en mouvement : action, temporalité et processus[END_REF][START_REF] Lorino | L'activité collective, processus organisant. Un processus discursif fondé sur le langage pragmastiste des habitudes[END_REF]. Of course, the hospital in which our intervention took place, like many others, is impacted by major structural changes of the French healthcare system, among which are staff shortage and limited resources which have seriously deteriorated work conditions for the past several years. What exacerbated the difficulties of the hospital was the deleterious management of the director and his support among members of the board which deteriorated the social relations. The employees, especially the medical professionals, tried to alert the board about the behaviors of the director but they were ignored. Even workers' representatives were unable to have a peaceful dialogue about work conditions with the director and the board. Given the magnitude of the social crisis that strongly impacted our approach and the dialogue with our client, we always sought not to lose sight of the real work. Although we didn't have the opportunity to analyze the activity as we had considered, we worked to create the conditions for a calm social dialogue based on real work in a form that we had not imagined, by regularly making

In the palliative care department, a fact that had affected all the department's employees was relayed about the director's management. In a meeting concerning the department's organization, the nurses said that more of them were needed to enable work under good conditions. As an example, they stated that they could not leave the department at lunchtime because that would mean leaving just one nurse in the department who, if ever a patient fell from his bed, could not take care of him alone to put him back into his bed. The only answer they obtained from the director was that the patient could stay on the ground for 30 minutes, waiting for the second nurse to come back from lunchtime and help his/her colleague. All the employees that had heard the director's answer were shocked, leaving some of them in tears. methodological adjustments to ensure that our approach was always fitting the pace of our client. As the qualitative data of our pre-diagnosis was simply not accepted, we decided to generate quantitative data that could not be fully rejected. The questionnaire forced us to get out of our comfort zone but was the best strategy to continue our intervention and to encourage employees to share their point of view about their work conditions. For us, the ergonomists, the diagnosis resulting from the questionnaire was the best way to encourage our client's representatives to meet the employees in the departments, where real work was accomplished daily. In a form of iterative process, the feedback sessions were then spaces where real work could be debated to produce new qualitative data. These elements are the basis of the pedagogical approach that constitutes ergonomics intervention [START_REF] Dugué | L'intervention ergonomique comme acte pédagogique[END_REF]. They describe a situated engineering of the ergonomic intervention and show the importance of an approach based on an experiential pedagogy, where the participants are actors in the understanding of their work system and experiment new forms of collective action. Such an approach is part and parcel of an awareness-raising process by leading the various stakeholders of the institution to "access a global awareness of all the elements, personal and structural, that contribute or have contributed to their difficulties" (Vallerie & Le Bossé, 2006, p. 90), and thus contributes to opening up the spectrum of opportunities for action, i.e., to the development of their power to act [START_REF] Bossé | soutenir de développement du pouvoir d'agir des personnes et des collectivités[END_REF]. Our objective of co-constructing spaces for debate on work was partially achieved since we succeeded in putting real work under discussion, encouraging the confrontation of divergent points of view and aiming for work conditions transformations. On the other hand, we were not able to deepen our work by establishing this type of debate in the existing organizational structure in a perennial way, and by organizing subsidiarity [START_REF] Mollo | Pratiques réflexives et développement des individus, des collectifs et des organisations[END_REF][START_REF] Rocha | Du silence organisationnel au débat structuré sur le travail : les effets sur la sécurité et l'organisation[END_REF]. Nevertheless, we know that our research-intervention had effects since the governance of the institution did consider and act on the main determinants from the diagnosis and feedback sessions, adopting a new posture learned during the action.

Keywords

Ergonomic intervention, work management, social crisis, social dialogue, spaces for debate.

Figure 1 :

 1 Figure 1: example of the incidence of lack of equipment on an employee's perception of quality of work

© The 2023 Organizational Design And Management Congress(ODAM 2023)

.travail-emploi.gouv.fr/enquete-source/la-surveillance-medicale-des-expositions-des-salaries-aux-risquesprofessionnels-2


est destinée au dépôt

Prediction of cheese-making properties of bulk milk

according to farming practices.

Lucille Rey-Cadilhac, Claire Laurent, M Gelé, S Léger, Anne Ferlay

To cite this version:

Lucille Rey-Cadilhac, Claire Laurent, M Gelé, S Léger, Anne Ferlay.

  Prediction of cheese-making properties of bulk milk according to farming practices L. Rey-Cadilhac 1 , C. Laurent 1 , M. Gelé 2 , C. Laithier 2 , S. Léger 3 and A. Ferlay 1 1 Université d'Auvergne, INRAE, VetAgro Sup, UMR1213 Herbivores, 63122 St-Genes-Champanelle, France, 2 Institut de l'Elevage, 149 rue de Bercy, 75595 Paris Cedex12, France, 3 Université Clermont Auvergne, Laboratoire de Mathématiques Blaise Pascal, UMR6620-CNRS, 63178 Aubière Cedex, France; lucille.rey@vetagro-sup.fr somatic cells. Surveys focused on feed management, herd characteristics and conditions of milking and milk storage on

Prediction of cheese-making properties of bulk milk according to farming practices.. 72nd Annual meeting of European Federation of Animal Science, Swiss Organizing Committee of EAAP, Aug 2021, Davos, Switzerland. 10.3920/978-90-8686-918-3. hal-04220940 J.J. Liu 1 , M.P. Ellies-Oury 1,2 and J.F. Hocquette 1 1 INRAE, UMR1213, 63122 Theix, France, 2 Bordeaux Sciences Agro, 1 cours du Général de Gaulle, 33175 Gradignan, France; jingjing.liu@inrae.fr consuming extensive animal products. Hence, they are more open to eat plant-based substitutes and probably cell-based interest about cell-based meat, China is regarded as a potential market by Western private companies to develop celltype of meat substitutes including cell-based meat in China.


V A Sugiawati

Vacandio

Perrin-Pellegrino

A Galeyeva

A P Kurbatov

Djenizian

Sputtered porous Li-fe-p-o film cathodes prepared by Radio frequency Sputtering for Li-ion Microbatteries

the increasing demands from micro-power applications call for the development of the electrode materials for Li-ion microbatteries using thin-film technology. Porous Olivine-type LiFePO 4 (Lfp) and nASicon-type Li 3 fe 2 (po 4 ) 3 have been successfully fabricated by radio frequency (Rf) sputtering and post-annealing treatments of LFP thin films. The microstructures of the LFP films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the LFP films were evaluated by cyclic voltammetry and galvanostatic charge-discharge measurements. The deposited and annealed thin film electrodes were tested as cathodes for Li-ion microbatteries. It was found that the electrochemical performance of the deposited films depends strongly on the annealing temperature. The films annealed at 500 °C showed an operating voltage of the porous LFP film about 3.45 V vs. Li/Li + with an areal capacity of 17.9 µAh cm -2 µm -1 at C/5 rate after 100 cycles. porous nASicon-type Li 3 fe 2 (po 4 ) 3 obtained after annealing at 700 °C delivers the most stable capacity of 22.1 µAh cm -2 µm -1 over 100 cycles at C/5 rate, with an operating voltage of 2.8 V vs. Li/Li + . the post-annealing treatment of sputtered LFP at 700 °C showed a drastic increase in the electrochemical reactivity of the thin film cathodes vs. Li + , leading to areal capacity ~9 times higher than as-deposited film (~27 vs. ~3 µAh cm -2 µm -1 ) at C/10 rate.

Li-ion microbatteries have emerged a new direction for powering the miniaturized modern devices, for instance RFID tags, implantable medical devices, microsensors, and smart cards. In order to advance towards the fabrication of all-solid-state thin film microbatteries, numerous studies have been reported to find innovative cathode and anode materials. Most of reports have been largely devoted to anode materials such as self-organized TiO 2 nanotubes 1,2 , silicon nanowires [START_REF] Laïk | Silicon nanowires as negative electrode for lithium-ion microbatteries[END_REF] , Cu 2 Sb 4 , aluminum nanorods [START_REF] Oltean | A Li-Ion Microbattery with 3D Electrodes of Different Geometries[END_REF] , carbon nanotubes [START_REF] Sharifi | Hierarchical self-assembled structures based on nitrogen-doped carbon nanotubes as advanced negative electrodes for Li-ion batteries and 3D microbatteries[END_REF][START_REF] Sugiawati | Electrodeposition of polymer electrolyte into carbon nanotube tissues for high performance flexible Li-ion microbatteries[END_REF] , and LiNiVO 4 [START_REF] Reddy | Effect of Substrate Temperature on Morphology and Electrochemical Performance of Radio Frequency Magnetron Sputtered Lithium Nickel Vanadate Films Used as Negative Electrodes for Lithium Microbatteries[END_REF] . Besides the anode materials, exploiting the cathode materials are very crucial to realize the fabrication of full cell Li-ion microbatteries. Iron-based phosphate especially olivine-type LiFePO 4 (LFP) becomes a popular cathode as it is known to be cheap, abundant, low toxic, and thermally stable [START_REF] Padhi | Phospho olivines as Positive-Electrode Materials for Rechargeable Lithium Batteries[END_REF] . The strong Fe-O covalent bonds in LFP cathodes has such a special characteristic compared to layered LiCoO 2 -type materials [START_REF] Ni | Polyanion-Type Electrode Materials for Sodium-Ion Batteries[END_REF] . Indeed, this covalent bond greatly improve the stability of O in the lattice, thus increasing the reliability of the materials.

In the field of thin-film microbatteries, study the properties of the pure active layers deposited onto the current collectors is essential since neither binder nor conductive additive are utilized [START_REF] Li | Highly oriented LiFePO 4 thin film electrodes via chemical solution deposition[END_REF][START_REF] Sugiawati | Porous NASICON-Type Li 3 Fe 2 (PO 4 ) 3 Thin Film Deposited by RF Sputtering as Cathode Material for Li-Ion Microbatteries[END_REF][START_REF] Fujimoto | Fabrication of solid-state thin-film batteries using LiMnPO 4 thin films deposited by pulsed laser deposition[END_REF] . By using the thin film cathodes, the intrinsic drawbacks such as a low electronic conductivity and low Li + diffusion mobility can also be suppressed because the thickness of the cathode material is considerably reduced [START_REF] Sugiawati | Sputter-Deposited Amorphous LiCuPO 4 Thin Film as Cathode Material for Li-ion Microbatteries[END_REF][START_REF] Zhu | Preparation and Characteristics of LiFePO 4 Thin Film by Radio Frequency Magnetron Sputtering for Lithium Microbatteries[END_REF][START_REF] Bouwman | Influence of Diffusion Plane Orientation on Electrochemical Properties of Thin Film LiCoO 2 Electrodes[END_REF] . Much studies have reported the growth of thin-film electrodes by various techniques such as pulsed laser deposition (PLD) [START_REF] Iriyama | Preparation of LiFePO 4 Thin Films by Pulsed Laser Deposition and Their Electrochemical Properties[END_REF][START_REF] Yada | Electrochemical properties of LiFePO 4 thin films prepared by pulsed laser deposition[END_REF][START_REF] Lu | Pulsed Laser Deposition and Electrochemical Characterization of LiFePO 4 -Ag Composite Thin Films[END_REF][START_REF] Sun | Needle-like LiFePO 4 thin films prepared by an off-axis pulsed laser deposition technique[END_REF][START_REF] Palomares | LiFePO 4 thin films grown by pulsed laser deposition: Effect of the substrate on the film structure and morphology[END_REF][START_REF] Deng | Electrochemical performance of LiNi 1/3 Co 1/3 Mn 1/3 O 2 thin film electrodes prepared by pulsed laser deposition[END_REF] , sputtering [START_REF] Xie | Li-ion diffusion kinetics in LiFePO 4 thin film prepared by radio frequency magnetron sputtering[END_REF][START_REF] Chiu | Optimization of Synthesis Process for Carbon-Mixed LiFePO 4 Composite Thin-Film Cathodes Deposited by Bias Sputtering[END_REF] and sol-gel [START_REF] Rho | Preparation of Li 4 Ti 5 O 12 and LiCoO 2 thin film electrodes from precursors obtained by sol-gel method[END_REF][START_REF] Kim | Fabrication of LiCoO 2 thin films by sol-gel method and characterisation as positive electrodes for Li/LiCoO 2 cells[END_REF][START_REF] Park | Preparation of LiMn 2 O 4 thin films by a sol-gel method[END_REF] . Among these different approaches, radio frequency (RF) sputtering technique is considered to be the most versatile way to fabricate thin-film cathodes [START_REF] Bouwman | Influence of Diffusion Plane Orientation on Electrochemical Properties of Thin Film LiCoO 2 Electrodes[END_REF][START_REF] Bates | Preferred Orientation of Polycrystalline LiCoO 2 Films[END_REF] because the sputtering parameters are easily controlled to obtain a good quality film, such as sputtering power, argon pressure, and substrate temperature during deposition.

More recently, RF sputtering have attracted substantial attention in the fabrication of the flexible and transparent thin-film batteries. For example, Lee et al. [START_REF] Lee | Scalable fabrication of flexible thin-film batteries for smart lens applications[END_REF] reported a flexible battery applied on contact lens using LFP cathode material deposited on the flexible polyimide substrate by RF sputtering, the thin film reached 63.8% of the theoretical capacity without carbon coating and the cell showed stable performance under wet conditions. Also, Oukassi et al. [START_REF] Oukassi | Transparent Thin Film Solid-State Lithium Ion Batteries[END_REF] deposited transparent thin film batteries layers using RF sputtering, a discharge capacity of 0.15 mAh at C/2 rate with an average capacity loss of solely 0.15% per cycle can be obtained.

Due to a strong research interest focused on searching for lithium transition metal phosphates as cathode materials, NASICON type-Li 3 Fe 2 (PO 4 ) 3 has been reported of having a high lithium mobility and can intercalate up to two moles of lithium within the structure [START_REF] Cabana | Effect of ball-milling and lithium insertion on the lithium mobility and structure of Li 3 Fe 2 (PO 4 ) 3[END_REF] . Besides a theoretical capacity of 128 mAh g -1 32 , Li 3 Fe 2 (PO 4 ) 3 cathode is currently attracting considerable interest due to several advantages such as low toxicity, low cost, good ionic conductivity, and large natural abundance [START_REF] Yang | Effect of VO43-substitution for PO43-on electrochemical properties of the Li 3 Fe 2 (PO 4 ) 3 cathode materials[END_REF] . Furthermore, the structure of the NASICON type-Li 3 Fe 2 (PO 4 ) 3 is more stable than that of olivine-type LiFePO 4 [START_REF] Salah | Local structure and redox energies of lithium phosphates with olivine-and Nasicon-like structures[END_REF] and its synthesis is easier as it can be prepared directly in air. NASICON type-Li 3 Fe 2 (PO 4 ) 3 have been commonly synthesized via various methods such as solid-state reactions [START_REF] Sun | Characterization of Nasicon-type Li 3 Fe 2-2x Ti x Mn x (PO 4 ) 3/C cathode materials[END_REF] , hydrothermal [START_REF] Yang | Hydrothermal synthesis of lithium iron phosphate cathodes[END_REF] , sol-gel combustion [START_REF] Karami | Synthesis, characterization and application of Li 3 Fe 2 (PO 4 ) 3 nanoparticles as cathode of lithium-ion rechargeable batteries[END_REF] and ultrasonic spray pyrolysis [START_REF] Ivanov-Schitz | Li 3 Fe 2 (PO 4 ) 3 solid electrolyte prepared by ultrasonic spray pyrolysis[END_REF] . However, there are only limited reports regarding the Li 3 Fe 2 (PO 4 ) 3 film deposited by RF Sputtering [START_REF] Sugiawati | Porous NASICON-Type Li 3 Fe 2 (PO 4 ) 3 Thin Film Deposited by RF Sputtering as Cathode Material for Li-Ion Microbatteries[END_REF] . In the present work, we propose to study the effect of annealing temperature on RF sputtered LFP thin-films in terms of morphology, composition, structure, and electrochemical properties. We show that the thermal treatment performed at 700 °C in air leads to the formation of porous Li 3 Fe 2 (PO 4 ) 3 showing the best electrochemical performance and therefore being a good candidate as a cathode for Li-ion microbatteries.

Results and Discussion

Structural and chemical characterization. The schematic representation of the sputtering system is illustrated in Fig. 1. The sputtering process can be briefly described as follows: an inert argon gas is introduced in the vacuum chamber and the ionization process leads to the formation of a plasma. Then, the energized ions hitting the LFP target (cathode) eject out adatoms that are deposited on the substrate to form a thin film. Various parameters such as the nature of the substrate, the sputtering power, the argon pressure, the duration, and the deposition temperature have significant influences on the growth rate and features of the deposited film [START_REF] Sugiawati | Sputter-Deposited Amorphous LiCuPO 4 Thin Film as Cathode Material for Li-ion Microbatteries[END_REF] .

In this work, a sputtering power of 3 W cm -2 and argon pressure of 7 mTorr during 12 hours of deposition was employed to obtain smooth and dense layers as well as a better adhesion between the films and the substrates. Owing to a low deposition rate, 12 hours of deposition is required to obtain LFP films with a sufficient thickness for the targeted application. The XRD pattern of the commercial LFP target and as-deposited film are plotted in Fig. 2a. Obviously, the initial target has well-defined peaks corresponding to the Olivine LiFePO 4 (JCPDS File No. 040-1499). However, after deposition at room temperature, only Ti peaks can be identified suggesting that the material is amorphous. The amorphous nature of the thin films deposited without heating treatment, either substrate heating during deposition or post-annealing have been reported in previous studies [START_REF] Sugiawati | Porous NASICON-Type Li 3 Fe 2 (PO 4 ) 3 Thin Film Deposited by RF Sputtering as Cathode Material for Li-Ion Microbatteries[END_REF][START_REF] Sugiawati | Sputter-Deposited Amorphous LiCuPO 4 Thin Film as Cathode Material for Li-ion Microbatteries[END_REF] . Thus, the thermal treatment step is essential because the crystalline materials are known for their better electrochemical reactivities versus Li ions [START_REF] Tintignac | High performance sputtered LiCoO 2 thin films obtained at a moderate annealing treatment combined to a bias effect[END_REF] .

Figure 2b,c display the SEM images of the thin films deposited at 3 W cm -2 W during 12 hours. As-deposited film shows a dense layer with a thickness of approximately 1.6 µm that corresponds to a growth rate of 2.2 nm min -1 . EDX analysis after deposition (Fig. 2d) revealed a Fe:P atomic ratio of 14.33(1): 14.58 (1), which is in agreement with the LFP formula. To further study in detail the effects of the annealing temperature, the as-deposited LFP films were annealed at 400 °C, 500 °C, 600 °C, and 700 °C, respectively in air atmosphere for one hour. In agreement with the previous studies, as-deposited films show poor crystallinity. As the films are annealed, the adsorbed atom on the surface of the films are activated and rearranged to form ordered crystal structure [START_REF] Chiu | Structural evolution and electrochemical performance of LiFePO 4/C thin films deposited by ionized magnetron sputtering[END_REF] . The XRD patterns for the LFP films are gathered in Fig. 3 for analyzing the effects of the thermal treatment at various temperatures on their crystal structure. At first glance, the typical peaks ascribable to crystalline LFP and Li 3 Fe 2 (PO 4 ) 3 phases can be detected at elevated temperatures. The amorphous nature of LFP is evidenced for the film annealed at 400 °C since only Ti peaks are visible. This result confirms that annealing temperature higher than 400 °C is required to crystallize LFP thin film [START_REF] Fujimoto | Fabrication of solid-state thin-film batteries using LiMnPO 4 thin films deposited by pulsed laser deposition[END_REF] . As the temperature was increased to 500 °C, several characteristic peaks of 2θ suited at 17.21°, 20.82°, 25.65°, 29.87° and 32.36° marked as symbol (o) are attributed to the (0 2 0), (0 1 1), (0 2 1), (1 2 1) and (0 3 1) planes of LFP phase. Besides the presence of LFP peaks, two small Li 3 Fe 2 (PO 4 ) 3 peaks with low intensities marked as symbol (*) are also detected at 2θ of 24.4° and 35.8° suggesting that the decomposition of LiFePO 4 phase has also started. Nevertheless, crystalline LFP seems to be the most predominant phase at 500 °C. This is probably due to a slow heating rate that is applied during annealing treatment. As reported elsewhere [START_REF] Sauvage | Origin of electrochemical reactivity enhancement of post-annealed LiFePO 4 thin films: Preparation of heterosite-type FePO4[END_REF] , the heating rate plays an important role in decelerating a second phase formation. It is important to note that in our work the films were heated at 2 °C min -1 to avoid the fast formation of Li 3 Fe 2 (PO 4 ) 3 phase due to the LFP sensibility to air atmosphere. Thus, the LFP phase can be clearly detected at 500 °C after annealing in air atmosphere. Presumably, Li 3 Fe 2 (PO 4 ) 3 phase might be quickly obtained when the heating rate is faster than 2 °C min -1 in air. When the annealing temperature further raised to 600 °C, more Li 3 Fe 2 (PO 4 ) 3 (JCPDS file no. 047-0107) peaks have appeared. The annealed films at 600 °C are assumed to be composed of mixed LFP and Li 3 Fe 2 (PO 4 ) 3 phases. In a good agreement with the previous reports [START_REF] Iriyama | Preparation of LiFePO 4 Thin Films by Pulsed Laser Deposition and Their Electrochemical Properties[END_REF][START_REF] Yada | Electrochemical properties of LiFePO 4 thin films prepared by pulsed laser deposition[END_REF][START_REF] Chiu | Optimization of Synthesis Process for Carbon-Mixed LiFePO 4 Composite Thin-Film Cathodes Deposited by Bias Sputtering[END_REF][START_REF] Sauvage | Origin of electrochemical reactivity enhancement of post-annealed LiFePO 4 thin films: Preparation of heterosite-type FePO4[END_REF] , the optimum annealing temperature for the crystallization of LFP was 500 °C. As expected, by increasing the annealing temperature up to 700 °C, almost all phases are transformed to Li 3 Fe 2 (PO 4 ) 3 due to the oxidation of Fe 2+ by oxygen from air according to Eq. ( 1) [START_REF] Sugiawati | Porous NASICON-Type Li 3 Fe 2 (PO 4 ) 3 Thin Film Deposited by RF Sputtering as Cathode Material for Li-Ion Microbatteries[END_REF] .

+ → + 12LiFePO 3O 4Li Fe (PO ) 2Fe O (1) 4 2 3 2 4 3 2 3
Another LFP phase with very low intensity at 2θ = 20.82° is detected as minor phase. However, the peak intensity appears to be weakening at this temperature. As previously reported [START_REF] Hamelet | The effects of moderate thermal treatments under air on LiFePO 4 -based nano powders[END_REF] , encouraging results on the electrochemically active Li 3 Fe 2 (PO 4 ) 3 phase that obtained after annealing at 700 °C have been studied in the form of composite electrodes carrying polymer binder and carbon additive. NASICON-type Li 3 Fe 2 (PO 4 ) 3 can be considered as an interesting cathode material for Li-ion batteries by hosting about 2 additional Li + (Fe 3+ /Fe 2+ redox couple) with great reversibility at a voltage plateau of around 2.8 V [START_REF] Xie | Li-ion diffusion kinetics in LiFePO 4 thin film prepared by radio frequency magnetron sputtering[END_REF][START_REF] Chiu | Optimization of Synthesis Process for Carbon-Mixed LiFePO 4 Composite Thin-Film Cathodes Deposited by Bias Sputtering[END_REF][START_REF] Rho | Preparation of Li 4 Ti 5 O 12 and LiCoO 2 thin film electrodes from precursors obtained by sol-gel method[END_REF][START_REF] Kim | Fabrication of LiCoO 2 thin films by sol-gel method and characterisation as positive electrodes for Li/LiCoO 2 cells[END_REF][START_REF] Park | Preparation of LiMn 2 O 4 thin films by a sol-gel method[END_REF] . However most reports on this material focus on composite Li 3 Fe 2 (PO 4 ) 3 cathodes prepared by slurry coatings instead of thin films.

In-depth structural studies have been also carried out by in-situ XRD experiments. The purpose of this particular structural analysis is to follow the evolution of the formed phases at elevated temperature after deposition time of 3 hours. The different XRD patterns given in Fig. 4 were acquired during annealing process between 400 °C and 700 °C using steps of 20 °C. Starting from 400 °C, a low intensity peak corresponding to LFP appeared at 2θ = 35.90°. In fact, Li 3 Fe 2 (PO 4 ) 3 starts to crystallize at 420 °C which is shown by the presence of a small peak at 2θ = 35.36° with a low crystallinity. Both Li 3 Fe 2 (PO 4 ) 3 and LFP peaks can be clearly observed in the temperature range between 560 °C and 640 °C, mainly the stronger peak intensity located at 2θ = 20.82° for LFP phase and 2θ = 24.14° for Li 3 Fe 2 (PO 4 ) 3 phase. Then, the intensities of both peaks are getting weaker and even disappeared when annealing temperatures are higher than 640 °C or lower than 560 °C. This temperature range is considered to be less preferred for the Li ion intercalation/de-intercalation in the cathode materials. At the temperature below 560 °C, the presence of LFP phase is more pronounced, on the contrary when the annealing temperature is higher than 640 °C the appearance of Li 3 Fe 2 (PO 4 ) 3 phase becomes predominant. Similar results on the LFP powders were observed by Hamelet et al. [START_REF] Hamelet | The effects of moderate thermal treatments under air on LiFePO 4 -based nano powders[END_REF] and Delacourt et al. [START_REF] Delacourt | The existence of a temperature-driven solid solution in Li x FePO 4 for 0 ≤ x ≤ 1[END_REF] , demonstrating the significant decomposition of the LFP phase occurred on thermal treatment at temperatures greater than ~ 500 °C and the progressive sharpening peaks for the Li 3 Fe 2 (PO 4 ) 3 can be observed afterwards. Bünting et al. [START_REF] Bünting | Influence of titanium nitride interlayer on the morphology, structure and electrochemical performance of magnetron-sputtered lithium iron phosphate thin films[END_REF] reported that the Ti interdiffusion occured during the crystallization process of the LFP thin film, leading to the LiTi 2 (PO 4 ) 3 (LTP) phase formation. From the XRD pattern, the reflection peaks at 2θ = 20.82° and 2θ = 24.4° which overlap with the reflection peaks of LFP and Li 3 Fe 2 (PO 4 ) 3 are characteristics for LTP phase [START_REF] Yu | LiTi 2 (PO 4 ) 3/C Anode Material with a Spindle-Like Morphology for Batteries with High Rate Capability and Improved Cycle Life[END_REF] .

As the electrochemical performance of electrodes are often driven by their morphology, the examination of thin-films was performed by SEM. Figure 5 shows the surface of the annealed thin films. Apparently, the roughness increases with increasing of the annealing temperature.

According to the SEM examinations, LFP-400 is composed of small grains and exhibits a rough surface due to an inhomogeneous size distribution of particles (Fig. 5a,b). As the temperature is raised to 500 °C, the surface is characterized by the presence of large pores with various diameters (Fig. 5c,d), suggesting the formation of crystalline LFP phase [START_REF] Sauvage | Origin of electrochemical reactivity enhancement of post-annealed LiFePO 4 thin films: Preparation of heterosite-type FePO4[END_REF][START_REF] Guan | Synthesis of porous nano/micro structured LiFePO 4/C cathode materials for lithium-ion batteries by spray-drying method[END_REF] . As the temperature reaches 600 °C, the microstructured deposit is highlighted by appearance of grain boundaries with various grain sizes. After annealing at 700 °C, the surface becomes coarse and highly porous, which is consistent with the formation of the NASICON-type Li 3 Fe 2 (PO 4 ) 3 phase 12 . From the above results, it is interesting to note that the texture of LFP thin films shows some cracks except for the sample annealed at the highest temperature. electrochemical characterization. Cyclic voltammetry (CV) experiments were performed to evaluate the influence of the annealing process on the reactivity of LFP films with Li + . Figure 6 shows the voltammograms obtained from the first cycle. No redox peak can be identified for LFP-0 (Fig. 6a) confirming that amorphous LFP is not electrochemically active. A similar behavior is observed for LFP-400 (Fig. 6b) suggesting that amorphous LFP is predominant despite the detection of a small peak by in-situ XRD which is attributed to the crystalline LFP phase. The LFP-500 film showed a well-defined peak pair and reversible redox peaks at 3.65 V and 3.33 V vs. Li/ Li + corresponding to the anodic and cathodic peaks, respectively (Fig. 6c). These peaks are typical for the oxidation and reduction reactions of olivine-type LiFePO 4 material with Li + according to Eqs (2) and (3) [START_REF] Wu | Electrochemical Behavior of LiFePO 4 Thin Film Prepared by RF Magnetron Sputtering in Li 2 SO 4 Aqueous Electrolyte[END_REF] . The low potential difference between the oxidation and reduction peaks (∆Ep) about 0.32 V vs. Li/Li + indicates that the film reveals a good electrochemical reversibility for Li + intercalation/de-intercalation. In addition, a broad peak pair with very low absolute current densities can also be observed at 2.79 V for the oxidation peak and 2.81 V for the reduction peak. These peaks correspond to the reaction of Li ions with the Li 3 Fe 2 (PO 4 ) 3 phase.

- - → + - + - Oxidation: LiFePO xLi xe xFePO (1 x)LiFePO (2)
As the annealing temperature increases from 500 °C to 600 °C, a small oxidation peak at 3.48 V and a reduction peak at 3.42 V which are attributed to the two-phase transformation of the (Fe 3+ /Fe 2+ ) redox couple due to the reversible intercalation of Li ions in the LFP crystal structure (Fig. 6d) are progressively vanished. This result is in good agreement with the XRD data showing that the LFP phase is clearly observable at 600 °C while the complete transformation into Li 3 Fe 2 (PO 4 ) 3 phase has yet to be occurred. In addition, a pair of anodic and cathodic peaks at around 2.29 V and 2.26 V vs. Li/Li + could be attributed to the formation of the iron tavorite phase LiFePO 4 (OH) [START_REF] Sugiawati | Porous NASICON-Type Li 3 Fe 2 (PO 4 ) 3 Thin Film Deposited by RF Sputtering as Cathode Material for Li-Ion Microbatteries[END_REF][START_REF] Wang | Nature of LiFePO 4 aging process: Roles of impurity phases[END_REF][START_REF] Asl | Phosphorous acid route synthesis of iron tavorite phases, LiFePO 4 (OH) x F 1-x [0 ≤ x ≤ 1] and comparative study of their electrochemical activities[END_REF][START_REF] Marx | The structure of tavorite LiFePO 4 (OH) from diffraction and GGA + U studies and its preliminary electrochemical characterization[END_REF] according to Eq. ( 4)

+ → + 2LiFePO 2H O 2LiFePO (OH) H (4) 4 2 4 2
Thin film annealed at 700 °C (Fig. 6e) reveals a peak pair, a reduction peak at 2.77 V and an oxidation peak at 2.82 V which are attributed to the reversible intercalation reactions of Li + ions into Li 3 Fe 2 (PO 4 ) 3 as described by Eq. ( 5) [START_REF] Sugiawati | Porous NASICON-Type Li 3 Fe 2 (PO 4 ) 3 Thin Film Deposited by RF Sputtering as Cathode Material for Li-Ion Microbatteries[END_REF] . The cathodic and anodic peaks are symmetric and have similar current density values, indicating the excellent degree of reversibility. In a good agreement with the XRD analysis, due to the interdiffusion between the Ti and the deposited LFP thin film, the additional cathodic peak at 2.38 V and anodic peak at 2.42 V are observable at 600 °C and 700 °C which are characteristics for the LiTi 2 (PO 4 ) 3 [START_REF] Yu | LiTi 2 (PO 4 ) 3/C Anode Material with a Spindle-Like Morphology for Batteries with High Rate Capability and Improved Cycle Life[END_REF] phase, according to Eq. ( 6) Preliminary CV results highlight that LFP thin films performances are strongly related to their structure and morphology. Indeed, the capacities of thin films prepared under different conditions varied significantly. Figure 7 shows the typical charge-discharge profiles of the five cathode thin films in the potential range 2-4 V at a current rate of C/10. In accordance with the CV curves, no voltage plateau can be observed for LFP-0 and LFP-400, delivering very low capacity values (<10 µAh cm -2 µm -1 ). More remarkably, a couple of defined charge-discharge plateaus at 3.3 and 3.5 V are clearly seen at 500 °C corresponding to the reversible intercalation of lithium ions in crystallized LiFePO 4 . These charge-discharge plateaus are fully consistent with the peaks of the CV curves. In many previous reports, crystalline LFP films can be obtained after annealing under inert atmosphere. In this work, the presence of the LFP phases can be detected after annealing treatment in air atmosphere. This result suggests that the phase transformation is slower, probably due to the low heating rate applied during the annealing treatment as previously mentioned. The capacities values for the 1 st , 2 nd , and 3 rd cycles are 39 µAh cm -2 µm -1 , 37 µAh cm -2 µm -1 and 37 µAh cm -2 µm -1 with the corresponding coulombic efficiencies of 88%, 90% and 88%, respectively. The slight decrease of the coulombic efficiency is probably due to the small amount of Li 3 Fe 2 (PO 4 ) 3 phase that has been evidenced by XRD analysis.

= + + - + Li Fe (PO ) Li Li Fe (PO ) e (5)
= + + + - Li Ti (PO ) LiTi (PO ) 2Li 2e (6)
For LFP-600, the voltage plateau around 2.8 V is ascribed to the reaction implying the Li 3 Fe 2 (PO 4 ) 3 phase. The presence of a short plateau at 3.5 V can be attributed to the low amount of crystalline LFP. The capacities of the LFP film annealed at 600 °C for the 1 st , 2 nd , and 3 rd cycles are 27 µAh cm -2 µm -1 , 20 µAh cm -2 µm -1 and 18 µAh cm -2 µm -1 and the coulombic efficiencies are 57%, 80% and 84%, respectively. The low coulombic efficiency obtained in the 1 st cycle could be explained by the mixed phases. In addition, the LFP film annealed at 700 °C revealed a well-defined plateau around 2.4 V which indicates the Li ions insertion into the LiTi 2 (PO 4 ) 3 lattice structure and another plateau appeared at 2.8 Vcorresponds to redox reactions involving the Li 3 Fe 2 (PO 4 ) 3 phase [START_REF] Masquelier | New Cathode Materials for Rechargeable Lithium Batteries: The 3-D Framework Structures Li 3 Fe 2 (XO 4 ) 3 (X = P, As)[END_REF][START_REF] Padhi | Mapping of Transition Metal Redox Energies in Phosphates with NASICON Structure by Lithium Intercalation[END_REF][START_REF] Padhi | Effect of Structure on the Fe 3+ /Fe 2+ Redox Couple in Iron Phosphates[END_REF] . The capacities of the film for the 1 st , 2 nd , and 3 rd cycles are 31 µAh cm -2 µm -1 , 28 µAh cm -2 µm -1 and 27 µAh cm -2 µm -1 , while the associated coulombic efficiencies can reach 83%, 90% and 92%, respectively. Beyond the influence of the chemical and structural composition, the enhanced electrochemical properties of LFP-500 and LFP-700 can be explained by the porosity of the both layers. Actually, it has been reported that the use of porous electrodes can improve the electrochemical performance of batteries owing to the larger electrode/ electrolyte interface [START_REF] Legrand | Structural and textural characterization of LiFePO 4 thin films prepared by pulsed laser deposition on Si substrates[END_REF][START_REF] Sauvage | Effect of texture on the electrochemical properties of LiFePO 4 thin films[END_REF] . In the present case, the porous nature of the LFP-500 and LFP-700 films is supposed to promote the penetration of the electrolyte providing more reaction electrochemical actives sites for the lithium ions intercalation/de-intercalation owing to larger accessible surface of the thin films. This is beneficial to improve the Li ion exchange between the LFP film electrode and electrolyte because the pores serve as channels for fast lithium supply [START_REF] Zhou | A porous LiFePO 4 and carbon nanotube composite[END_REF] .

In order to have a better insight into the potential use of annealed LFP layer as cathode materials, rate capability and long-term cycling tests were carried out. Figure 8a confirms that LFP-400 film provides the lowest capacity values attaining only 2 µAh cm -2 µm -1 at the 50 th cycle. LFP-500 film exhibits the highest discharge capacities up to the 90 th cycle but this cathode is subjected to a continuous capacity loss with a drop after the 80 th cycle. The capacities obtained at the 1 st , 2 nd , and 100 th cycle are 36 µAh cm -2 µm -1 , 35 µAh cm -2 µm -1 , and 18 µAh cm -2 µm -1 , respectively. Thus, only half of the initial capacity is retained after 100 cycles. It can be noticed that similar behavior regarding the capacity fading has been reported for the annealed LiNi 1/3 Co 1/3 Mn 1/3 O 2 thin films at 500 °C22 . Such a low cycling stability may be ascribed to the poor adhesion strength between the thin film and the substrate that are combined to the presence of cracks, leading to the detachment of the layer from the current collector and the subsequent loss of electrical contact. For the LFP-600 film, the first discharge capacity is relatively high (29 µAh cm -2 µm -1 ) but severely drops to reach only 8 µAh cm -2 µm -1 after the 50 th cycle. This behavior could be attributed to the presence of cracks and mixed unstable LiFePO 4 and Li 3 Fe 2 (PO 4 ) 3 phases. Finally, LFP-700 film shows the best cycling stability. The capacities obtained for the LFP-700 were found to be 32 µAh cm -2 µm -1 for the first cycle and 22 µAh cm -2 µm -1 for the 100 th cycle corresponding to a capacity retention of around 70%. The good storage performance and the stability of the LFP-700 film could be mainly attributed to feature properties of the Li 3 Fe 2 (PO 4 ) 3 thin film. Compared to LFP-700 sample, the sharp capacity dropping of LFP-400, LFP-500 and LFP-600 in the first few cycles can be imputed to the cracks that are responsible for the poor mechanical properties. For more details, the areal capacity values and the capacity retention at the 50 th and 100 th cycles are summarized in Table 1.

As a further examination, we also studied the rate capability of the thin films annealed at 500 °C and 700 °C because they showed the most interesting electrochemical properties (Fig. 8b). LFP-500 delivers stable capacity values of 35 µAh cm -2 µm -1 at C/10 rate, 25 µAh cm -2 µm -1 at C/5 rate, and 13 µAh cm -2 µm -1 at 1C rate. Although the initial C/10 and C/5 discharge capacity are superior compared to LFP-700 film, the LFP-500 shows relatively larger degradation in capacity with further increasing discharge current. Indeed, significant capacity losses of 28% and 48% are observed for subsequent tests at C/5 and 1C rate, respectively. The LFP-700 film cathode delivers capacity values of 25 µAh cm -2 µm -1 at C/10 rate, 22 µAh cm -2 µm -1 at C/5 rate, and 19 µAh cm -2 µm -1 at 1C rate. The capacity slightly decreased of only 11% from C/10 to C/5 rate and decreased of about 15.5% from C/5 to 1C rate. More remarkably, the discharge capacity values of about 22 µAh cm -2 µm -1 and 25 µAh cm -2 µm -1 at C/5 and C/10 show that the full capacity is completely recovered even after fast cycling tests. Therefore, it is found that the highest annealing temperature treatment (700 °C) is able to strongly improve the electrochemical stability of LFP films electrodes, especially in the rapid charge-discharge regimes. After few initial cycles, LFP-700 film reveals high reversibility and prominent cycling stability. The better performance of LFP-700 film is also attributed to the presence of the LTP phase as a good ionic conductor [START_REF] Zając | Towards control over redox behaviour and ionic conductivity in LiTi 2 (PO 4 ) 3 fast lithiumion conductor[END_REF] .

To sum up, the amorphous and partially crystalline LFP phases may not be stable during Li-ion intercalation/ de-intercalation, yielding in a fast capacity fading [START_REF] Deng | Electrochemical performance of LiNi 1/3 Co 1/3 Mn 1/3 O 2 thin film electrodes prepared by pulsed laser deposition[END_REF] . Thus, through this study, we highlight the important role of the post annealing treatment mainly for the intercalation cathodes. This treatment is responsible for the film texturation, thus it could help minimizing ionic limitation by enhancing the contact area between electrolyte and the film surface contact, as well as could enhance the electrochemical activity [START_REF] Sauvage | Effect of texture on the electrochemical properties of LiFePO 4 thin films[END_REF][START_REF] Nanjundaswamy | Synthesis, redox potential evaluation and electrochemical characteristics of NASICON-related-3D framework compounds[END_REF][START_REF] Andersson | Lithium insertion into rhombohedral Li 3 Fe 2 (PO 4 ) 3[END_REF][START_REF] Morcrette | On the way to the optimization of Li 3 Fe 2 (PO 4 ) 3 positive electrode materials[END_REF] .

conclusion

In summary, we have successfully prepared porous thin film cathodes by RF sputtering technique and subsequent annealing treatment in air atmosphere. The electrochemical performance of the thin films depends strongly on the annealing conditions. Different morphological and structural properties were obtained by varying the temperature treatment, leading to a significant influence on the cell performances. We report that annealing at 500 °C is required to obtain porous olivine type-LiFePO 4 film even if the electrochemical tests revealed a drop of capacities after the 80 th cycle. Complete transformation from porous olivine type-LiFePO 4 to porous NASICON-type Li 3 Fe 2 (PO 4 ) 3 occurring at 700 °C led to a remarkable stability of the electrode with good electrochemical performance even at fast kinetics.

Methods

Preparation of LFP thin films. Thin films were deposited on Ti foil substrate by radio frequency sputtering in a Plassys MP 300 apparatus at room temperature. In the present work, radio-frequency (RF) sputtering is utilized to deposit LFP layers from a commercial target. The target was LiFePO 4 (LFP) purchased from Neyco, purity 99.9%. Prior to their insertion in the deposition chamber, Ti foils were cleaned by ultrasonication in acetone, 2-propanol, and methanol for 10 minutes each. Pre-sputtering of the targets before deposition was employed to remove the native oxide layer. Before deposition, vacuum was applied into the sputtering chamber until the pressure was around 3 × 10 -6 mbarr. Sputtering was performed in a pure argon atmosphere. The argon pressure was set to 7 mTorr and the applied RF sputtering power was fixed to 75 W (3 W cm -2 ). Deposition time was adjusted for 12 hours. The post-annealing treatment was carried out at various temperatures (400 °C, 500 °C, 600 °C, and 700 °C) for one hour with a heating rate of 2 °C min -1 (Furnace: NABERTHERM Controller B 180). The as-deposited thin film was labelled as LFP-0 and post-annealed thin films at 400 °C, 500 °C, 600 °C and 700 °C were labelled as LFP-400, LFP-500, LFP-600, and LFP-700, respectively.

Materials characterization.

The crystalline structure of the initial LiFePO 4 target and as-deposited film were analyzed by X-ray diffraction in a D5000 BRUKER-SIEMENS diffractometer with Cu-Kα radiation (wavelength = 1. 5406 Å) over 2θ range of 10-70°. The accelerating voltage and current were 40 kV and 30 mA, respectively and a scan speed of 0.04° per second was utilized. The in-situ X-ray diffraction measurement was also performed on an X'Pert diffractometer with Cu-Kα radiation. As-deposited LFP film was mounted on an adapted furnace and annealed from 400 °C to 700 °C with an interval of 20 °C. The data were collected every 300 s with scan-step size 0.04°. The diffractogramms were analyzed using JCPDS-ICDD (Joint Committee on Powder Diffraction Standards-International Center for Diffraction Data). Morphological properties of the thin films were characterized by Scanning Electron Microscopy (SEM) using a field-emission scanning electron microscope (Ultra-55 Carl Zeiss).

electrochemical measurements. All cells were assembled in an argon-filled glove box (MBraun, Germany) with H 2 O and O 2 contents were less than 0.5 ppm. The electrochemical properties of the LFP thin films (LFP-0, LFP-400, LFP-500, LFP-600, and LFP-700) were evaluated by cyclic voltammetry (CV) and chronopotentiometry using a VMP3 potentiostat (Bio Logic, France). For the electrochemical tests, two-electrode Swagelok cells were assembled using the LFP thin films as the working electrode while metallic lithium foils served as both the counter and the reference electrodes. It is important to specify that the electrodes were not mixed with any additive and binder. The working and counter electrodes were separated by a Whatman glass microfiber soaked in the liquid organic electrolyte composed of 1 mol L -1 of LiPF 6 in ethylene carbonate (EC) -diethyl carbonate (DEC) (1:1 in w/w). The area of the LFP films was 0.49 cm 2 and the average thickness of the film was ca. 1.6 µm, measured from cross section SEM images. The CV measurement was performed in the potential range between 2 and 4 V at a scan rate of 0.1 mV s -1 and galvanostatic cycling with potential limitation (GCPL) was performed in the potential range in the same potential window at multiple C-rates (C/10, C/5, C/2 and 1C). The charge or discharge rate denoted as C/n means that the battery is fully charged or discharged up to its total storage capacity in n hours, whilst C-rate of the LFP films were calculated by estimating the weight of active material in the thin film from the film thickness and the density of 3.6 g cm -3 .

Figure 1 .

 1 Figure 1. Schematic representation of a RF sputtering system.

Figure 2 .

 2 Figure 2. XRD patterns of the commercial LFP target and as-deposited LFP film (a), SEM images of asdeposited LFP film from the top view (b), and cross-sectional view (c) and EDX analysis of the as-deposited LFP film (d).

Figure 3 .

 3 Figure 3. XRD patterns of LFP thin films annealed at various temperatures in air for one hour.

Figure 4 .

 4 Figure 4. In-situ XRD patterns (λ = 1.54 Å) of as-deposited LFP film during thermal annealing performed between 400 and 700 °C by step of 20 °C.

Figure 5 .

 5 Figure 5. SEM images the annealed films at different temperatures LFP-400 (a,b), LFP-500 (c,d), LFP-600 (e,f) and LFP-700 (g,h).

4 4 4 Figure 6 .

 46 Figure 6. Cyclic voltammograms (1 st cycle) of the LFP-0 film (a), LFP-400 (b), LFP-500 (c), LFP-600 (d) and LFP-700 (e).

Figure 7 .

 7 Figure 7. Charge-discharge profiles of the LFP-0 film (a), LFP-400 film (b), LFP-500 film (c), LFP-600 film (d) and LFP-700 film (e).

Figure 8 .

 8 Figure 8. Long-term cycling stability study showing capacity versus the cycle number at C/5 rate for the various annealed LFP thin films (a), and rate capability of LFP-500 and LFP-700 films at multiple C-rates (b).

Table 1 .

 1 Electrochemical properties of LFP films annealed at various temperatures.

		400 °C	500 °C	600 °C	700 °C
	Discharge capacity of the 1 st cycle (µAh cm -2 µm -1 )	8	36	29	32
	Discharge capacity of the 50 th cycle (µAh cm -2 µm -1 )	2	28	8	24
	Discharge capacity of the 100 th cycle (µAh cm -2 µm -1 )	-	18	-	22
	Capacity retention (%) 1 st -50 th cycle	25	78	29	75
	Capacity retention (%) 1 st -100 th cycle	-	50	-	70

Scientific RepoRtS | (2019) 9:11172 | https://doi.org/10.1038/s41598-019-47464-2

Acknowledgements

This work is financially supported by the Région SUD.

Author contributions

T.D. and F.V. supervised the work. V.A.S. conducted the experiments. C.P., A.G., and A.P.K. contributed to the discussion. All authors have reviewed the manuscript.

Additional information

Competing Interests: The authors declare no competing interests.

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