Rémi Moulian

Martha Chacón-Patiño

Oscar Lacroix-Andrivet

Sandra Mounicou

Anna Luiza

Mendes Siqueira

Carlos Afonso

Ryan Rodgers

Pierre Giust

Brice Bouyssiere

Caroline Barrère-Mangote

Speciation of Metals in Asphaltenes by High-Performance Thin-Layer Chromatography and Solid-Liquid Extraction Hyphenated with Elemental and Molecular Identification

Keywords: MALDI, Porphyrins, Asphaltenes, HPTLC, Vanadium, FT-ICR MS, LA-ICP-MS

ABSTRACT (267 words)

Asphaltenes are among the most challenging components in petroleum processing because they contain high amounts of heteroatoms (i.e., S, N, O, V, and Ni) thought to be responsible for strong aggregation tendencies, precipitation, and fouling problems. The role of vanadium and nickelcontaining petroleum compounds (i.e., "petroporphyrins") in aggregation and fouling is not completely understood because asphaltene composition and structure is still a subject of debate in the petroleum chemistry community. Characterization of asphaltenes, namely, molecular analysis that employs no chromatographic separation, often fails to reveal their comprehensive composition. The work herein presents asphaltene fractionation by 1) solid/liquid extraction, which allows for separation of single-core ("island") and multicore ("archipelago) structural motifs, and 2) high-performance thin layer chromatography (HPTLC) with cellulose as the stationary phase and DCM/MeOH as the eluent, which facilitates access to petroporphyrins.

Characterization is performed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and matrix-assisted laser desorption ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI FT-ICR MS). The results demonstrate that even with multiple separation steps, a large quantity of vanadyl porphyrins remains inaccessible for molecular analysis by MALDI FT-ICR MS, which raises the question of what portion of a complex sample of asphaltene can be revealed by ultrahigh resolution mass spectrometry. Furthermore, the results show that easily accessible porphyrins migrate with the solvent front in HPTLC. Thus, HPTLC can be used to isolate and identify "free" porphyrins, not locked into asphaltene aggregates; however, further development of separation methods is required to access the most difficult and problematic asphaltene fractions, which do not migrate and impose analytical challenges due to their stronger aggregation tendency.

INTRODUCTION (772 words)

Asphaltenes are well known for their negative impact on petroleum production, transportation, storage, and refining. Asphaltenes contain a wide diversity of molecules with different degrees of aromaticity, heteroatom contents, and molecular structure. For instance, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has revealed asphaltene molecules with either single-core or multicore structures that contain only hydrogen and carbon (hydrocarbons or the HC class) as well as species with up to three or more heteroatoms (e.g., vanadyl porphyrins or the N4O1V1 class, sulfur-containing molecules or the S3 class, and oxygen-rich compounds or the O4 class) [START_REF] Strausz | About the Colloidal Nature of Asphaltenes and the MW of Covalent Monomeric Units[END_REF]- [START_REF] Ghislain | Characterization of crude oil asphaltenes by coupling size-exclusion chromatography directly to an ultrahigh-resolution mass spectrometer: Characterization of crude oil asphaltenes[END_REF]. Thus, the combined effects of aromaticity, heteroatom content, and molecular structure trigger multiple intermolecular interactions, such as pi-stacking, hydrogen bonding, acidbase conjugations, and London dispersion forces between asphaltenes. The synergy between multiple intermolecular interactions results in strong aggregation and ultimate precipitation of a wide compositional range of species, from those with no heteroatoms (HC class) to high heteroatom-containing species [START_REF] Mckenna | Heavy Petroleum Composition. 4. Asphaltene Compositional Space[END_REF], [START_REF] Yarranton | On the Size Distribution of Self-Associated Asphaltenes[END_REF], [START_REF] Gray | Supramolecular Assembly Model for Aggregation of Petroleum Asphaltenes[END_REF]. It is believed that metals present in asphaltenes are mainly present in porphyrinic complexes [START_REF] Borisova | Role of Vanadylporphyrins in the Flocculation and Sedimentation of Asphaltenes of Heavy Oils with High Vanadium Content[END_REF]- [START_REF] Freeman | Identification of metalloporphyrins by third-derivative UV/VIS diode array spectroscopy[END_REF], i.e., nickel and vanadyl porphyrins are tetrapyrrole-based metal complexes. The actual structures of nickel and vanadyl porphyrins are the result of geochemical modifications of the chlorophyll molecule. The chlorophyll structure changed over geological time during fossil crude oil formation via demetallation, aromatization, and peripheral addition of sulfur or oxygen [START_REF] Filby | Geochemistry of Metal Complexes in Petroleum, Source Rocks, and Coals: An Overview[END_REF], [START_REF] Lash | Geochemical origins of sedimentary benzoporphyrins and tetrahydrobenzoporphyrins[END_REF]. These transformations yielded several structurally different porphyrin families of the types N4O1V1, N4O2V1, N4O3V1, N4O1V1S1 and N4Ni1, as shown in Figure 1.

Understanding the molecular composition of porphyrins and other metal complexes that trigger issues in refinery processes is critical to the petroleum industry. For this purpose, it is essential to fractionate asphaltenes before molecular-level analysis because direct "dilute-and-shoot" studies of such a complex matrix usually do not reveal a great part of the information. As shown by Evdokimov et al [START_REF] Evdokimov | Assembly of asphaltene molecular aggregates as studied by near-UV/visible spectroscopy[END_REF], [START_REF] Evdokimov | Occlusion of Foreign Molecules in Primary Asphaltene Aggregates from Near-UV-Visible Absorption Studies[END_REF], even with the abundant presence of petroporphyrins, the Soret band, characteristic of porphyrinic complexes in ultraviolet absorption spectra, is not always detected in the sample spectrum, the detection of which depends on the dilution factor. Furthermore, with MS techniques such as matrix-assisted laser desorption ionization (MALDI) FT-ICR MS, the matrix, ionization efficiency, and ion suppression effects usually conceal the molecular level of difficultto-ionize compounds. Recently, Chacón-Patiño et al [START_REF] Chacón-Patiño | High Resolution Mass Spectrometric View of Asphaltene-SiO 2 Interactions[END_REF] and Giraldo-Davila et al [START_REF] Giraldo-Dávila | Correlations between Molecular Composition and Adsorption, Aggregation, and Emulsifying Behaviors of PetroPhase 2017 Asphaltenes and Their Thin-Layer Chromatography Fractions[END_REF] used silica gel thin-layer chromatography plates to separate asphaltene samples and achieve a more complete molecular characterization. The authors used a mixture of DCM/MeOH, followed by toluene, to separate asphaltenes into three fractions enriched in alkyl-aromatic compounds, polar species, and noneluted asphaltenes. This technique can also be used on the preparative scale to separate fractions that can then be extracted with solvents and further analyzed by other techniques (Li et al [START_REF] Li | Thin-layer chromatography of pitch and a petroleum vacuum residue[END_REF]). Furthermore, asphaltene samples can also be separated prior to high-performance thin layer chromatography (HPTLC) analysis. For example, Chacón-Patiño et al [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 3. Dominance of Island or Archipelago Structural Motif Is Sample Dependent[END_REF], [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 2: Selective Separation Method That Reveals Fractions Enriched in Island and Archipelago Structural Motifs by Mass Spectrometry[END_REF], [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 1: Asphaltenes Are Composed of Abundant Island and Archipelago Structural Motifs[END_REF] reported asphaltene fractionation by a solid-liquid extraction strategy using silica gel as an adsorbent and subsequent Soxhlet extraction; this method is known as extrography. The authors demonstrated that extrography allows for the separation of asphaltenes according to their structural motif, multicore or archipelago (composed of several aromatic cores linked by covalent bonds) and single-core or island (composed of one aromatic core with alkyl side chains). According to these results, island compounds are easily accessed by atmospheric pressure photoionization FT-ICR MS; conversely, archipelago molecules are more difficult to ionize, due in part to their relatively stronger aggregation trends [START_REF] Chacón-Patiño | The Compositional and Structural Continuum of Petroleum from Light Distillates to Asphaltenes: The Boduszynski Continuum Theory As Revealedby FT-ICR Mass Spectrometry[END_REF].

The use of TLC or HPLTC allows for more comprehensive elemental information for petroleum fractions [START_REF] Günther | Recent trends and developments in laser ablation-ICP-mass spectrometry[END_REF], [START_REF] Vorapalawut | Application of TLC and LA ICP SF MS for speciation of S, Ni and V in petroleum samples[END_REF]. For instance, Chirinos et al [START_REF] Chirinos | Determination of Vanadium/Nickel Proportionality in the Asphaltene Fraction of Crude Oil Using Thin-Layer Chromatography with Femtosecond Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry[END_REF] used laser ablation ICP-MS to achieve rapid determination of the ratio between nickel and vanadium in asphaltene samples after a separation step with HPTLC. Moreover, the use of HPTLC plates also allows for molecular analysis by LDI/MALDI FT-ICR MS; for example, Cho et al [START_REF] Cho | Evaluation of Laser Desorption Ionization Coupled to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry To Study Metalloporphyrin Complexes[END_REF] demonstrated that LDI FT-ICR MS can be used to quantify porphyrins in petroleum samples. Additionally, Pradilla et al [START_REF] Ramírez-Pradilla | Electron-Transfer Ionization of Nanoparticles, Polymers, Porphyrins, and Fullerenes Using Synthetically Tunable α-Cyanophenylenevinylenes as UV MALDI-MS Matrices[END_REF] developed a MALDI matrix to promote selective ionization or petroporphyrins via electron transfer reactions.

The authors used a novel matrix to analyze asphaltenes after an HPTLC separation step. The results revealed the selective ionization of petroporphyrins and an increased number of molecular formulas compared to those identified in previous studies [START_REF] Ramírez-Pradilla | Comprehensive Petroporphyrin Identification in Crude Oils Using Highly Selective Electron Transfer Reactions in MALDI-FTICR-MS[END_REF].

In this work, two successive separation steps, extrography and HPTLC, were coupled with elemental laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and molecular detection (MALDI FT-ICR MS) to characterize metals contained in one asphaltene reference sample, referred to as Asphaltene 2017. The purpose was to determine which fractions contained vanadium and the kinds of porphyrins present in these fractions.

EXPERIMENTAL SECTION (818 WORDS)

Samples and Reagents. Samples. Asphaltene 2017 (from a Middle Eastern crude oil, Vanadium content: 640 ppm) from the interlaboratory study of the Petrophase 2017 Conference [START_REF] Putman | Analysis of Petroleum Products by Gel Permeation Chromatography Coupled Online with Inductively Coupled Plasma Mass Spectrometry and Offline with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry[END_REF] and its extrography fractions, prepared as reported by Chacon-Patiño [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 3. Dominance of Island or Archipelago Structural Motif Is Sample Dependent[END_REF], [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 2: Selective Separation Method That Reveals Fractions Enriched in Island and Archipelago Structural Motifs by Mass Spectrometry[END_REF], were studied. Asphaltene

Solid/liquid extraction samples

Extrography fractionation was carried out following a method reported elsewhere [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 2: Selective Separation Method That Reveals Fractions Enriched in Island and Archipelago Structural Motifs by Mass Spectrometry[END_REF]. Briefly, a Soxhlet apparatus was used to perform three successive extractions. Approximately 150 mg of asphaltenes was dissolved in dichloromethane, and 15 g of silica was then added to the solution.

Subsequently, the mixture was completely dried under nitrogen, and the dried mixture was Soxhlet extracted with acetone, toluene/heptane (50/50 Hep/Tol, v/v), and toluene/tetrahydrofuran/methanol (47.5/47.5/5 Tol/THF/MeOH, v/v/v).

Instrumentation.

HPTLC Plates.

Cellulose HPTLC glass plates (Merck, thickness 0.15-0.2 mm, Frankfurter Strasse Darmstadt, 64293, Germany) that were 20 cm × 10 cm in size and did not contain fluorescent indicators were used. The HPTLC procedure was carried out with the following instrumentation protocol from CAMAG. Sample application and sample development were performed using automatic TLC Sampler 4 (ATS4) and automated multiple development 2 (AMD2) equipment.

UV absorbance chromatograms were acquired at a wavelength of 280 nm with a D2 & W lamp TLC scanner. UV spectra from 190 nm to 900 nm were obtained using the same device. Finally, a TLC visualizer was used to obtain images of the cellulose plate under 366 nm UV light after development. Peak area data were determined using WinCATS software.

HPTLC plates were cleaned with DCM and THF and dried at 110 °C for 10 min prior to sample deposition. All the samples were deposited 10 mm from the bottom of the plate. A high eluentstrength mobile phase (DCM:MeOH, 99.5:0.5) was used. The plate was developed in a single step until the solvent front reached 50 mm. Whole Petrophase 2017 and its extrography fractions were deposited two times per HPTLC plate on three different plates that were developed as described above for subsequent analysis by LA-ICP-MS.

Developed HPTLC separations for whole Petrophase 2017 and its three extrography fractions were also subjected to MALDI FT-ICR MS analysis. After separation, the different samples were scratched from the plates, and extraction using THF was performed and mixed with a custom synthetized MALDI matrix (matrix:sample ratio of 1) developed by the Combariza Research Group [START_REF] Ramírez-Pradilla | Comprehensive Petroporphyrin Identification in Crude Oils Using Highly Selective Electron Transfer Reactions in MALDI-FTICR-MS[END_REF], [START_REF] Ramírez-Pradilla | Electron-Transfer Ionization of Nanoparticles, Polymers, Porphyrins, and Fullerenes Using Synthetically Tunable α-Cyanophenylenevinylenes as UV MALDI-MS Matrices[END_REF], [START_REF] Giraldo-Dávila | Selective ionization by electron-transfer MALDI-MS of vanadyl porphyrins from crude oils[END_REF]. The MALDI matrix, facilitated porphyrin ionization by electron transfer reactions and is known as α-cyanophenylenevinylene (α-CNPV-CH3).

LA-ICP-MS

Element-specific analyses of the developed HPTLC plates were carried out by LA-ICP-MS using a New Wave Research UP-213 Nd:YAG laser (ESI, Fremont, CA) coupled with ICP-MS (7700 series, Agilent, Santa Clara, CA) [START_REF] Vorapalawut | Application of TLC and LA ICP SF MS for speciation of S, Ni and V in petroleum samples[END_REF] under the operating conditions given in Table 1. The instrument was equipped with a Fassel-type quartz torch shielded with a grounded Pt electrode and a quartz bonnet; a standard quartz injector (1.75 mm i.d.) was used. An ablation chamber was installed on a three-axis translation stage and coupled to the ICP torch using a 60 cm Tygon tube (5.0 mm i.d.). The ablated material was swept by the carrier gas (helium) and mixed with the spectrometer makeup gas (argon) prior to introduction into the plasma. Ni sampler (orifice diameter: 1.1 mm) and skimmer (orifice diameter: 0.8 mm) cones were optimized for the analyses [START_REF] Vorapalawut | Application of TLC and LA ICP SF MS for speciation of S, Ni and V in petroleum samples[END_REF]. The laser beam followed a linear trajectory throughout the migration. To fit within the ablation cell, plates were cut to dimensions of 9×10 cm 2 . Each sample on the three different plates was analyzed in triplicate.

MALDI FT-ICR MS

A hybrid quadrupole FT-ICR instrument (SolariXR, Bruker Daltonics, Bremen, Germany) equipped with a 12 T superconducting magnet was equipped with an LDI/MALDI source with an Nd:YAG × 3 solid-state laser (355 nm) [START_REF] Lacroix-Andrivet | Comparison of Silica and Cellulose Stationary Phases to Analyze Bitumen by High-Performance Thin-Layer Chromatography Coupled to Laser Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry[END_REF]. Broadband mass spectra were acquired over a mass

HPTLC results

Four asphaltene samples, the whole Petrophase 2017 asphaltene sample (A2017) and its three extrography fractions (acetone, Hep/Tol, and Tol/THF/MeOH), were separated via HPTLC and analyzed with a UV densitometer. UV analysis at 280 nm of the developed HPTLC plates (Figure 2 A) demonstrates that the samples were separated into two major fractions, eluted and noneluted. demonstrate that all noneluted fractions have a similar spectrum, in which the absorbance reaches a maximum at ~240 nm and then decreases continuously until ~800 nm. However, the eluted HPTLC fractions present different trends. For instance, the Tol/THF/MeOH extrography fraction features an absorption spectrum with a weaker signal between 400 and 600 nm than those of the other fractions. Eluted species from whole PetroPhase 2017 and its Hep/Tol extrography fraction present similar absorption spectra. Finally, the acetone extrography fraction shows the Soret band (~420 nm, indicated with a star), which is characteristic of porphyrins.

Table 2 shows the results for average quantification for the three developed HPTLC plates.

Combined with the data shown in Figure 2, the results indicate that only ~9% of the Tol/THF/MeOH extrography fraction migrates up to the solvent front. For the acetone fraction, there is 53% migration. Whole asphaltenes and their Hep/Tol fraction present a similar migration of 28 and 23%, respectively. The results suggest that species in the acetone fraction are less prone to strong adsorption issues on polar surfaces such as cellulose. 3 demonstrate that ~100% of 51 V-containing compounds (~20,000 cps) in the acetone fraction migrated to the solvent front, whereas 100% of vanadium species in the Tol/THF/MeOH (~30,000 cps) fraction remained noneluted.

Trends of Elemental

Molecular-Level Characterization by FT-ICR MS

MALDI FT-ICR MS characterization was facilitated by the use of a novel matrix designed to favor electron transfer reactions for the efficient ionization of metal complexes, such as vanadyl porphyrins [START_REF] Ramírez-Pradilla | Comprehensive Petroporphyrin Identification in Crude Oils Using Highly Selective Electron Transfer Reactions in MALDI-FTICR-MS[END_REF], [START_REF] Ramírez-Pradilla | Electron-Transfer Ionization of Nanoparticles, Polymers, Porphyrins, and Fullerenes Using Synthetically Tunable α-Cyanophenylenevinylenes as UV MALDI-MS Matrices[END_REF]. This MALDI matrix is a phenylenevinylene derivative that allows for greater ion abundances of porphyrin-like molecules and limits the ionization of other compounds, such as alkyl-substituted PAHs, which are also present in asphaltenes. MALDI FT-ICR spectra were collected for all samples at the deposition point (noneluted fraction) and the solvent front (eluted fraction). Molecular formulas were assigned to the mass spectral peaks and sorted by heteroatom class (e.g., N4O1V1 or vanadyl porphyrins), carbon number, and double bond equivalents (DBE = number of rings plus double bonds). At the sample deposition point (noneluted fraction), porphyrins were not detected in the whole asphaltene sample or in all extrography fractions. Thus, at the deposition point, vanadium-containing compounds detected by LA-ICP-MS were not ionized (as monomers) by MALDI, even when utilizing a specific matrix designed to enhance the ionization of vanadyl porphyrins. The results highlight the limitations of mass spectrometry to access the complete molecular composition of one of the most complex/challenging samples, the asphaltenes. for all samples present the same carbon number (29/30) and DBE values [START_REF] Giraldo-Dávila | Correlations between Molecular Composition and Adsorption, Aggregation, and Emulsifying Behaviors of PetroPhase 2017 Asphaltenes and Their Thin-Layer Chromatography Fractions[END_REF]. Molecular formula for DBE for all the samples are presented in Table S1. Thus, the results suggest that the PetroPhase 2017 asphaltene sample contains abundant DPEP-type porphyrins.

DISCUSSION (829 words)

In Figure 2 B, the spectra obtained for the noneluted fractions for all samples are remarkably similar and are characteristic of a complex mixture of polyaromatic compounds. For the eluted HPTLC fractions, the Soret band at 420 nm was only evident in the acetone extrography fraction.

As shown by Evdokimov et al [START_REF] Evdokimov | Assembly of asphaltene molecular aggregates as studied by near-UV/visible spectroscopy[END_REF], porphyrins can be "invisible" in UV-Vis spectroscopy due to aggregation. Thus, our results suggest that separation by HPTLC allows for the isolation of porphyrins that are not bound in asphaltene aggregates, as already proposed in our previous paper [START_REF] Moulian | Speciation of Metals in Asphaltenes by High-Performance Thin-Layer Chromatography and Laser Ablation Inductively Coupled Plasma-Mass Spectrometry[END_REF].

For the whole PetroPhase 2017 sample, the results obtained by UV (Figure 2) and laser ablation (Figure 3) are quite similar to our previous results [START_REF] Moulian | Speciation of Metals in Asphaltenes by High-Performance Thin-Layer Chromatography and Laser Ablation Inductively Coupled Plasma-Mass Spectrometry[END_REF]. Indeed, nearly 80% of the vanadium remained at the deposition point (Table 3, LA-ICP-MS analysis). In that work, the Asphaltene 2017 sample was also analyzed by MALDI FT-ICR MS, but no porphyrins were detected at the deposition point. The results suggest that vanadium-containing molecules, such as porphyrins (whole asphaltenes/deposition point), are present but are not easily accessible, likely because of aggregation. These results are consistent with the UV spectroscopy behavior. Putman et al [START_REF] Putman | Probing Aggregation Tendencies in Asphaltenes by Gel Permeation Chromatography. Part 1: Online Inductively Coupled Plasma Mass Spectrometry and Offline Fourier Transform Ion Cyclotron Resonance Mass Spectrometry[END_REF] has reported limitations in MS characterization of asphaltenes due to low ionization efficiency of specific chromatography fractions. In this work, according to Table 3 and molecular formulas; such compounds could be completely "free" or present on the aggregate surface and therefore available for MS analyses. As reported by Chacon-Patiño [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 2: Selective Separation Method That Reveals Fractions Enriched in Island and Archipelago Structural Motifs by Mass Spectrometry[END_REF], the Tol/THF/MeOH extrography fraction contains abundant multicore motifs ("archipelago") and heteroatom-rich compounds. This fraction exhibits stronger aggregation trends and may comprise the most problematic asphaltene species that are likely responsible for demetallation problems in refineries.

Conversely, the acetone fraction presents the highest intensities for the three different types of porphyrins (Figure 4), and the Soret band present in the UV-Vis spectrum (Figure 2) at the eluted point suggests a high amount of easily accessible porphyrins. The most abundant molecular formulas have the same carbon number and DBE values as those found for other samples (whole asphaltenes, Hep/Tol, and Tol/THF/MeOH). These results suggest that the easily accessible porphyrins are likely the same compounds in all four samples and were concentrated in the acetone fraction, which exhibits weaker adsorption on polar surfaces (i.e., cellulose) and weaker aggregation tendencies than for the other solvents; therefore, it is likely that porphyrins were not locked into aggregates in this fraction. Furthermore, the UV results in Figure 2 A suggest that a portion of the sample (47%) remained at the deposition point, but no vanadium was found by the elemental LA-ICP-MS and molecular-level FT-ICR-MS analyses. These results suggest that Soxhlet extraction, coupled with HPTLC, allows for the separation of free porphyrins from those that are locked into asphaltene aggregates. The results indicate that the vanadium present in the acetone extrography fraction is easily accessible and constitutes "free" porphyrins. Chacon-Patiño et al [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 3. Dominance of Island or Archipelago Structural Motif Is Sample Dependent[END_REF] demonstrated that acetone fractions from geologically diverse asphaltene samples are enriched in single-core or "island" type asphaltenes [START_REF] Chacón-Patiño | Advances in Asphaltene Petroleomics. Part 2: Selective Separation Method That Reveals Fractions Enriched in Island and Archipelago Structural Motifs by Mass Spectrometry[END_REF]. Therefore, the results indicate that vanadyl porphyrins in the acetone fraction exhibit weak intermolecular interactions with asphaltene aggregates mostly comprised of single-core motifs; HPTLC separation by cellulose plates and DCM solvent can disrupt those interactions. Conversely, vanadyl porphyrins linked to multicore-type asphaltenes in the Tol/THF/MeOH extrography fraction are strongly linked to the nanoaggregates, which precludes their elution during HPTLC separation.

CONCLUSIONS (271 words)

Our previous works [START_REF] Moulian | Speciation of Metals in Asphaltenes by High-Performance Thin-Layer Chromatography and Laser Ablation Inductively Coupled Plasma-Mass Spectrometry[END_REF] using GPC-HPTLC with LA-ICP-MS suggest that porphyrins that migrate until the solvent front using DCM/MeOH were more accessible as free porphyrins than those that remained at the deposition point. Here, extrography followed by HPTLC separation was used on asphaltene samples. Then, molecular and elemental detection to analyze vanadium and vanadyl porphyrins was successfully used. The combination of molecular and elemental analyses proved that a large quantity of porphyrins remained inaccessible to molecular analyses because of matrix effects and ionization preferences and that these porphyrins are linked to "archipelago" asphaltenes. The MALDI FT-ICR MS analyses showed that in all the samples, porphyrins that migrate until the solvent front are easier to analyze than those that remain at the deposition point.

The acetone fraction showed a great quantity of easily ionizable porphyrins that migrated entirely until the solvent front. These results suggest that there was a high quantity of "free" porphyrins or porphyrins with weak interactions with the "island" nanoaggregates in the acetone fraction. In contrast, the Tol/THF/MeOH fraction, which contains a great quantity of vanadium, remains at the deposition point and gives almost no signal by MALDI-FT-ICR MS, which proves the strong interaction between porphyrins and "archipelago" type nanoaggregates or an effective occlusion of the porphyrins into the nanoaggregates. These results suggest that when ultrahigh-resolution mass spectrometry is used on asphaltene samples, even after previously using a separation step, only a part of the molecular complex structure can be revealed. Further works should concentrate on the noneluted part of the Hep/Tol and Tol/THF/MeOH fractions to determine the kinds of porphyrins present and their links with the asphaltene matrices.

TABLES

  2017 was obtained by a slightly modified version of the ASTM D6560-12 method. A cleaning step, via four cycles of maceration and Soxhlet extraction with heptane, was employed to decrease the amount of occluded/coprecipitated maltenes. Solvents. Tetrahydrofuran (THF, HPLC grade, without stabilizer, Lichrosolv, Merck, Frankfurter Strasse 250 Darmstadt, 64293, Germany) was used as the solvent for sample preparation and for MALDI analyses. Dichloromethane (DCM) and methanol (MeOH) (HPLC grade, Lichrosolv, Merck, Frankfurter Strasse 250 Darmstadt, 64293, Germany) were used to develop the HPTLC plates. Toluene, heptane, and pentane were used to prepare Petrophase asphaltenes. Acetone, toluene, heptane, THF and methanol of HPLC grade were used to prepare extrography fractions from Asphaltene 2017.

  range of m/z 147-1,000 with an accumulation of 200 scans. The signal was digitalized with 8 M points, resulting in a transient length of 3.4 s, giving a resolving power number of 0.9 10 6 at m/z 400. Instrument control and data acquisition were facilitated by DataAnalysis (version 4.4); OriginPro (version 2016) was used to process and visualize the data. From the molecular formulas determined from the accurate mass measurements (typically <0.2 ppm), double bond equivalent (DBE) values were calculated as shown in equation 1 (c: carbon number; h: hydrogen number; n: nitrogen number)[START_REF] Kim | Graphical Method for Analysis of Ultrahigh-Resolution Broadband Mass Spectra of Natural Organic Matter, the Van Krevelen Diagram[END_REF].

Figure 2 B

 2 Figure 2 B features the complete UV spectra for the eluted and noneluted fractions. The results

Figure 3 ,

 3 Composition as a Function of Migration. HPTLC plates were analyzed by LA-ICP-MS to quantify vanadium in the eluted/noneluted fractions. The results are presented in Figure S1 and summarized in Table 3, and corroborate compositional similarities between whole PetroPhase 2017 asphaltenes and its Hep/Tol extrography fraction (panels A and C): for both samples, 51 V is present at the deposition point (noneluted fraction) and the solvent front (eluted species). Regarding the acetone fraction, Figure 3 B demonstrates that all vanadiumcontaining compounds migrated with the solvent front. Conversely, the Tol/THF/MeOH fraction revealed vanadium compounds that remained in the noneluted HPTLC fraction. The quantitative results shown in Table

Figure 4

 4 Figure 4 presents isoabundance color-contoured plots of DBE versus carbon number for vanadyl

For 4 B

 4 the whole PetroPhase 2017 asphaltene sample, 146 molecular formulas were found; the most abundant compounds feature DBE values of 17 and 18, which indicates the dominance of Etio and DPEP porphyrins. The Hep/Tol and Tol/THF/MeOH extrography fractions only revealed 44 and 7 porphyrins species. Conversely, the acetone fraction featured the highest content of vanadyl porphyrins, as revealed by 254 molecular formulas obtained via mass spectrometry. In Figure , porphyrins with one additional oxygen atom were only found in whole asphaltenes and the acetone fraction with a 3.3 and 2.2-fold lower relative abundance than the N4O1V1 class.

Figure 4 C

 4 indicates that porphyrins with one sulfur atom, only detected in the acetone fraction, have abundant homologous series with DBE values from 22 to 30 and carbon numbers between 25 and 50. The higher DBE values are consistent with S incorporated as e.g., thiophene and benzothiophene peripheral groups.

Figure 4 A

 4 ,approximately 80% of molecules containing vanadium could not be identified via ultrahighresolution mass spectrometry. This raises questions about what portion can be analyzed with such techniques even with previous separation steps. Furthermore, in Figure4B, porphyrins with one additional oxygen atom were only found in PetroPhase 2017 sample and the acetone fraction in both case at the eluted point with a lower relative abundance (3.34 and 2.25 times less). The UV results for the Hep/Tol fraction were quite similar (Figure2) to those of the whole PetroPhase 2017 sample. However, according to elemental analysis, vanadium was present at a lower concentration at the eluted point (5%) for the Hep/Tol fraction than for the whole PetroPhase 2017 sample (20%). In MALDI-FT-ICR MS, the abundance of porphyrins at the eluted point was lower in the Hep/Tol fraction than in the whole sample. Collectively, the results suggest that the whole PetroPhase 2017 asphaltene sample and the Hep/Tol extrography fraction contained free and aggregate-bound porphyrins.HPTLC-LA-ICP-MS analysis (Figure3 D) of the Tol/THF/MeOH extrography fraction indicates that 51 V is only present at the deposition point; however, no Soret band was detected by UV-Vis spectroscopy (Figure2 B). For MALDI FT-ICR MS experiments, despite the use of the custom MALDI matrix for selective ionization of metal complexes, no porphyrins were detected at the deposition point. Thus, noneluted vanadium-containing compounds are not easily accessible and could be trapped into asphaltene aggregates that prevent their detection by UV-Vis spectroscopy and as monomers in FT-ICR MS. The eluted fraction (~8.8% in UV) from Tol/THF/MeOH presents a vanadium content below the LA-ICP-MS detection limit. However, it reveals 7 N4O1V1

FIGURESFigure 1 .

 1 FIGURES

Figure 2 .

 2 Figure 2. UV chromatograms at 280 nm (A) and UV spectra (D) and chromatograms (B) obtained

Figure 3 .

 3 Figure 3. Chromatograms obtained by HPTLC-LA-ICP-MS analysis at mass 51 for all four

Table 1 . LA-ICP MS Operating Parameters Agilent 7700 series ICP MS

 1

	Plasma Ar gas flow rate (L.min -1 )	15
	Auxiliary Ar gas flow rate (L.min -1 )	1
	Measured Isotope	13 C, 32 S, 51 V, 58 Ni, 60 Ni
	Analysis time (s)	506
	New Wave Research UP-213 LA
	Wavelength (nm)	213
	Fluence (J.cm -2 )	0.85
	Spot size (µm)	200
	Scan speed (µ.ms -1 )	100
	Carrier He gas flow rate (L.min -1 )	0.8

Table 2 .

 2 Results for UV analysis at 280 nm for all four samples with the average intensity for a total of 6 replicates and the RSD.

	Area 280 nm	Area at noneluted point	Area at eluted point	RSD at noneluted point (%)	RSD at eluted point (%)
	Whole PetroPhase 2017	19 000 (72%)	8 000 (28%)	11.1	23.4
	Tol/THF/MeOH fraction	15 000 (91.2%)	1 000 (8.8%)	7.4	16.9
	Hep/Tol fraction	19 000 (76.9%)	6 000 (23.1%)	6.6	19.8
	Acetone fraction	6 000 (47%)	8 000 (53%)	6.6	20.7

Table 3 .

 3 Results for LA-ICP-MS analysis at mass 51 for all four samples with the average intensity for a total of 6 replicates and the RSD

	Area 51 V	Area at noneluted point	Area at eluted point	RSD at noneluted point (%)	RSD at eluted point (%)
	Whole Petrophase 2017	552 000 (78.9%)	148 000 (21.1%)	11.4	9.8
	Tol/THF/MeOH fraction	667 000 (100%)	0 (0%)	6.3	0.0
	Hep/Tol fraction	500 000 (95.8%)	22 000 (4.2%)	2.3	31.9
	Acetone fraction	0 (0%)	143 000 (100%)	0.0	4.1

ACKNOWLEDGMENTS

The authors would like to thank TOTAL for supplying the oil samples. Work performed at the National High Magnetic Field Laboratory ICR User Facility was supported by the National Science Foundation Division of Chemistry through Cooperative Agreements DMR-1157490 and DMR-1644779 and the state of Florida. This work was also supported by Conseil Régional d'Aquitaine (20071303002PFM) and FEDER (31486/08011464). The authors would like to thank the EU for funding via the ERC PRIMCHEMproject (No. 636829). This work was supported at Chimie Organique Bioorganique Réactivité Analyse (COBRA) laboratory by the European Regional Development Fund (ERDF)N°31708, the Région Normandie, and the Laboratoire LabEx

Supporting Information

Figure S1. Six points calibration with vanadyl porphyrins after HPTLC separation and concentration obtained for the four samples by HPTLC-LA-ICP-MS. Table S1. Molecular formula, mass error and signal to noise ratio for all the vanadyl porphyrins signal at DBE 18 for all the four samples.

AUTHOR INFORMATION

Corresponding Author

Tel: +33 (0) 235 551 102 Email: caroline.mangote@total.com Tel: +33 (0) 559 407 752 Email: brice.bouyssiere@univ-pau.fr

Notes

The authors declare no competing financial interests SynOrg (ANR-11-LABX-0029). The authors would also like to thank Professor Marianny Y.

Combariza, University of Santander-Colombia, for providing the matrix used for MALDI analysis during this work.


Fabien Ferri

From reduced artificial intelligence to semiotic engineering: a new project for artificial intelligence

Keywords: Semiotic engineering, Artificial intelligence, Operational iconicity, Diagram, Phenomenology of knowledge

Following the reduced artificial intelligence programme carried out by Bruno Bachimont in the 1990s, we propose a new research programme: semiotic engineering. After having recalled in a first part the link of filiation which unites the first-generation reduced artificial intelligence programme to the semiotic engineering one, we return in a second part to the phenomenology of knowledge elaborated by C. S. Peirce to show in what way it constitutes a true methodological guide allowing the implementation of the semiotic engineering programme. Finally, in the third and last part, we show the limits of the first-generation reduced artificial intelligence programme and outline the principles for implementing semiotic engineering.

The discipline to which this article belongs is semiotic engineering: its objective is to design diagrammatic systems to help solve problems. The problem posed by such a discipline is the diversity of the knowledge it must involve, and the extent of its objects of study: all human activity is potentially concerned by its research programme. We will first define it as a technique of knowledge supports involving the sciences of culture to understand the problem-solving practices implemented in scientific, technical and ordinary practices. More precisely, this discipline develops graphic devices that allow problem solving mediated by the reading and interpretation of semiotic units of manipulation, graphic signs, and this through a type of reasoning that it gives rise to and allows for: diagrammatic reasoning.

Semiotic engineering is a descendant of reduced artificial intelligence (now abbreviated to reduced AI), an artificial intelligence research programme distinct from strong and weak artificial intelligence programmes, whose strategy was to instrument computer science in the automatic operationalisation of intelligent tasks [START_REF] Bachimont | L'artéfacture entre herméneutique de l'objectivité et de l'intersubjectivité : un projet pour l'intelligence artificielle[END_REF]. But unlike weak AI, semiotic engineering does not aim to instrument computer science. It aims to instrument the resolution practices operated by human beings thanks to the directly manipulable semiotic artefacts that are diagrams. Is the reproduction of a mind task by means of a technical device a model of the activity of the mind performing such a task or is it a simulation of the behaviour it reveals? Is it a simulation of the actual process of the mind performing it?

The questions of the reduced AI and its issues were the following: what knowledge is used by a minded agent in the context of a problem resolution (gnoseological issue)? What temporal organization does such a resolution require to be accomplished (methodological issue)? What is the share of formalizable knowledge in the set of phenomenological knowledge allowing the construction of a model of the knowledge system exploitable by the computer tool (scientific issue)? What program can be built from the formal knowledge drawn from the phenomenological model of resolution to make part of the problem resolution automatic, since a phenomenological content is not entirely reducible to a formal content (technological issue)? What are the phenomenological contents to be inferred from the result of the approximated resolution in order to make the resolution of the problem studied complete (hermeneutical issue)?

Reduced AI was engineering that set out to solve problems by computer by considering programs for what they do, i.e. solving problems by programming and operationalizing them within computing devices [START_REF] Bachimont | L'artéfacture entre herméneutique de l'objectivité et de l'intersubjectivité : un projet pour l'intelligence artificielle[END_REF]. It did not deal with all problems, but only those of a certain class. What was that class of problems?

Reduced AI focused on the class of problems involving linguistically conveyed phenomenological knowledge. Since it set itself the task of exploiting phenomenological knowledge for solving problems through computer science, it used scientific knowledge to address problems posed in terms of phenomenological knowledge.

Consequently, reduced AI started from a certain understanding of the notion of problem, according to which a problem is not a difficulty that requires the use of a supposedly natural faculty to be solved (intelligence), but a situation that requires the implementation of knowledge. It is easy to understand such an understanding, if one keeps in mind the following precaution followed by reduced AI: to abstain from any prior, a priori, thesis on the nature of intelligence or mind.

Indeed, if reduced AI had not described problem solving in terms of knowledge, then it would have described it in terms of process. But to describe resolution in terms of process is to tacitly posit a thesis about the nature of knowledge. This thesis consists in asserting that knowledge is an object of scientific ontology, either reducible to physical states (according to the physicalist position) or reducible to computational states (according to the computationalist position). To describe resolutions in terms of processes was to tacitly reduce knowledge to cognitive operations, hence to automatic actions that could be formalized algorithmically. But then what is knowledge related to a problem?

The only way to avoid falling into the reductionist trap while maintaining a truthful approach to knowledge was to consider knowledge for what it is in our most familiar everyday life: phenomenological content conveyed by linguistic idioms. The additional step taken by semiotic engineering consists in adding to the knowledge conveyed by linguistic statements graphical representations carrying a cognitive content that complements it. In this perspective, reduced AI becomes, in our opinion, semiotic engineering when it aims to rigorously articulate the idioms of natural languages with the contents of non-linguistic graphical representations in order to provide access to the contents lost by the formalism used as a principle of knowledge modelling (as soon as this principle is implemented). The application of this principle consists in reducing knowledge to the contents and logical structures of linguistic statements.

Peirce's phenomenology of knowledge: a methodological guide

In order to free ourselves from any theoretical prejudice or dogmatic posture, we have no other choice, in order to describe immediate, familiar and everyday informal problems, than to go in search of a phenomenology of knowledge, in the attention to what the evidence of practice gives us to see as know-how mobilizing tacit knowledge (which gives itself to be seen in tricks of the hand and silent gestures) and explicit knowledge (which gives itself to be listened to in linguistic expressions). This practice of doing and saying, in its tacit and explicit expressions, i.e. its apparent, and therefore describable, externalizations, is therefore what authorizes a public phenomenology, which can be the subject of a common study submitted to collective deliberation.

In its quest for a phenomenology of knowledge, reduced AI found in the phenomenology of knowledge elaborated at the beginning of the 20th century by C. S. Peirce [START_REF] Peirce | Écrits sur le signe[END_REF] a relevant research program that predicated a methodology that could also serve as a guide to semiotic engineering concerned with instrumenting the resolution of informal problems mobilizing phenomenological knowledge.

Semiotic engineering, as its name indicates, aims to place the problem of artificial intelligence within a semiotic framework, but without having recourse to computer artefacts. Intelligence is a multifaceted notion, which can be defined in many different ways, more or less arbitrarily, and loaded with presuppositions, even prejudices. In order to limit arbitrary decisions and presuppositions and question this behavioural manifestation, we need to start from the theoretical device that was set up by Peirce, enriching it with a technical understanding of the formats of graphic representations, in order to articulate linguistic representations to non-linguistic representations.

In response and reaction to the Kantian doctrine of categories, Peirce built a theoretical device at the foundation of a phenomenology of knowledge, called in his terminology phaneroscopy [START_REF] Peirce | Écrits sur le signe[END_REF]. Phaneroscopy deals with phanerons, which designate the modalities of presence of reality to a mind. It does not presuppose anything about the nature of the mind in question or about the ontological basis of reality. In the context of semiotic engineering, the semiotic formatting of the intuitive content that carries meaning proceeds jointly through graphic schematization (i.e. non-linguistic graphic representations) and conceptual categorization (i.e. linguistic graphic representations).

Peirce's phenomenology of knowledge is a phenomenology of the sign without a presupposed subject (substance) or predefined object (thing-in-itself). According to this phenomenology, all ontological reality is reduced to a manipulable sign carrying meaning. Moreover, everything that is a manipulable semiotic unit is spiritual, from the moment that the sign becomes the relay of an interpreting activity. Peirce calls this dynamic, vectored by inferences and bouncing from sign to sign, "semiosis". Semiosis is the potentially indefinite dynamic that carries the mind from sign to sign.

The semiotic break in this process is marked by the act, insofar as the act is what stops the interpretative process of semiosis in order to bring the human interpreter into the pragmatic order of action and practice, which is the order of existential finitude. The indefinite movement of interpretation is thus opposed to the finitude of action. More precisely the finitude of the action is the actualization of the act of interpretation in an effective operation realized. Interpreting in the context of semiotic engineering therefore means performing one or more technical operations whose operating modes are schematized by sign systems. These operations are guided by conventions that control the reading of the schemas so that they are actualized analogically by the persons who manipulates these schemas by reading them.

The whole challenge of semiotic engineering consists of schematizing the noncomputable operations of experience in order to model them, categorizing them linguistically in order to analyze them, and making them explicit discursively in order to characterize them, so that they can be implemented by intelligent semiotic agents. This is because it is a matter of transforming the content of these non-computable operations captured semiotically into cognitive tools that prescribe their correct manipulation. In other words, good semiotic manipulation is that which allows the reproduction of the operations of which the graphic symbols are the schemas, and which the interpreting subjects who manipulate them must implement. According to semiotic methodology, the association of ideas is no longer controlled by natural principles (resemblance, contiguity, causality) [START_REF] Hume | A Treatise of Human Nature[END_REF], but by inferences made between signs. What semiotic engineering proposes to make explicit are interpretive conventions that make it possible to systematize the relationships between knowledge and action through the manipulation of graphic signs that carry meaning.

Peirce's categories of being

Peirce thus distinguishes three ontological categories [START_REF] Peirce | Écrits sur le signe[END_REF]: 1° the firstness or being of the fact in its qualitative particularity (e.g. red); 2° the secondness or being of the actual raw fact, which implies the reciprocal action between two beings in the order of a mechanical causality (e.g. the sound waves that make the tympanum vibrate); 3° the thirdness or being of the law determining a future fact, i.e. the being of a third that allows a first one to interact with a second. Thirdness is the category of final causality, therefore that of intelligence. Why is this so?

Because it is the implementation of a third (diversions, means, representation, instrumental mediation, method, etc.) by a first (subject) in relation to a second (object, obstacle, danger, goal to be reached, problem to be solved). Indeed, there is intelligence as soon as there is mediation of a means. Intelligence thus supposes: 1° the representation of an object or a more or less complex situation causing an obstacle (problem); 2° the representation of the means to be implemented to remove and overcome it (intermediaries); 3° the representation of the end to be reached (the representation of the solution as a resolution of the problem). The representation of this end is, moreover, the bearer of information that retroacts in a recurrent causality on the intelligent being in the process of resolution: it continuously retroacts on the arrangement of the means implemented in the research process, in such a way that it adequately coincides with the content of the end aimed at by being fully adjusted to it. Any phenomenon that manifests thirdness behaviour, regardless of its degree of complexity, can therefore be described as intelligent.

Semiotic engineering is the construction of thirdness through the arrangement of semiotic units carrying meaning, which can be manipulated by human beings in semiotic systems whose functioning is activated by their operational reading. Thanks to their reading, these systems allow the implementation of the "diagramming" faculty [START_REF] Giardino | Diagramming: Connecting Cognitive Systems to Improve Reasoning[END_REF]. Diagramming refers to the ability to coordinate perceptual, motor and inferential processes during the operational reading of diagrams. This is why diagrams are both material supports (as captioned graphic diagrams) and generative methods (as prescriptive cognitive tools).

In other words, thirdness is the category of controlled interdependence, and therefore that of knowledge, since a problem is that which requires knowledge to be solved. Authentic thirdness is the category of effective knowledge (on the side of the interpreting subject) and observed thirdness is the category of objective intelligence (on the side of the observed phenomena). Authentic thirdness is what allows an objectification of the mind through signs materializing knowledge. The observed thirdness is the condition of possibility of a phenomenology of intelligence, since it manifests the logic of semiotic relations. This is why Peirce saw, for example, in the behaviour of a frog subjected to a scientific experiment the concrete operativity of an embodied syllogism [START_REF] Bachimont | L'artéfacture entre herméneutique de l'objectivité et de l'intersubjectivité : un projet pour l'intelligence artificielle[END_REF].

By identifying thought with a sign and intelligent operation with an inference between signs, we can therefore associate all semiotics with a dynamic material logic that allows for a phenomenology of knowledge and intelligence, from the moment a phenomenon (or phaneron in Peirce's language) meets the criterion of thirdness. It is this fact that semiotic engineering exploits as knowledge engineering, i.e. thirdness engineering.

Reduced AI: purpose, method, principles

The linguistic sign is the most commonly used in the expression and transmission of phenomenological knowledge because of its ease of manipulation and speed of transmission in intersubjective exchange. Therefore, the reduced AI was concerned with phenomenological knowledge as expressed through linguistic formulations. Its object was not the set of signs expressing knowledge, but the expression of knowledge as it is conveyed through the linguistic medium.

The project of semiotic engineering is to supplement reduced AI with nonlinguistic manipulable semiotic units, in order to allow diagrammatic reasoning, so that information processing is no longer carried exclusively by virtual computational machines, but by the living semiotic machines that we are as interpreting beings of meaning-bearing manipulable signs.

The objective of reduced AI was in fact to create knowledge-based computer systems whose function is to operationalize linguistically expressed phenomenological knowledge by implementing a formalist methodology governed by two principles [START_REF] Bachimont | Intelligence artificielle et écriture dynamique : de la raison graphique à la raison computationnelle[END_REF], the first of which was identified by the members of the Vienna Circle (the modelling principle) and the second by mathematical logic as it was accomplished in the mechanization of reasoning, thanks to the work of Turing (the effectivity principle). The principle of modelling indicated in what way the operational system of knowledge is a model of the problem treated; the principle of effectiveness specified in what way the model of the problem was operational, i.e. in what way the operationalization of the model in the computer device that implemented it referred to the effectiveness of the reality that the implemented model simulates.

Reduced AI, as the engineering of knowledge conveyed by linguistic representations, thus adopted a formalist method by resorting to a logicist conception of knowledge (formalism as a modelling principle) and a computational conception of logic (formalism as a principle of effectivity) [START_REF] Bachimont | Herméneutique matérielle et Artéfacture : des machines qui pensent aux machines qui donnent à penser[END_REF]. To adopt a logicist conception of knowledge is in fact to consider that the gnoseological truthful content of a linguistic expression is equivalent to its formal structure. In this perspective, common sense concepts have the same status as scientific concepts. What makes them common is the fact that their content is reducible to a formal structure, to the formal relation that structures it. Therefore, in order to extract the knowledge conveyed by linguistic expressions from natural language, it was sufficient to identify the formal structure of these expressions. By concatenating these structures in the canonical language of knowledge, formal logic, one could then construct a formal system of representation of the gnoseological content conveyed by the linguistically expressed phenomenological knowledge, and thus build a model of the problem for which this phenomenological knowledge is the resolution knowledge. Now, as any formal system is mechanizable on a Turing machine, any formal system is operational insofar as all the operations of the system are executable by a Turing machine. This is why computational formalism gave knowledge engineering the principle of effectivity it needed.

If the principle of effectivity did not pose a problem, on the other hand the principle of modelling did. Indeed, operationalizing the formal model of the phenomenological knowledge system implied having identified primitive notions, which resulted from an interpretation of their meaning in the irreducibly singular phenomenological context from which they were extracted. This meant that the formalization of the knowledge system was not a modelling in the strong sense, but a construction proceeding from a prior modelling that had fixed the meaning of the primitive notions of the model. In other words: what became invariable for the formal model became variable from the point of view of the resolution context, since each resolution context was recognized as an irreducibly singular interpretation context.

3. Limits of reduced AI and principles of semiotic engineering 3.1 The example of the concept of function in the context of medical knowledge modelling For example [START_REF] Bachimont | Intelligence artificielle et écriture dynamique : de la raison graphique à la raison computationnelle[END_REF], if we are in a medical setting and we need to model knowledge in the conceptual graph formalism from their linguistic expressions such as "Logroton contains chlortalidone" (a) and "chlortalidone has a diuretic function" (b):

[Logroton] -(contains) --> [chlortalidone] (a) [chlortalidone] -(has_the_function) --> [diuretic function] (b)
From the inference rule that a drug has the function of its active ingredient we would like to deduce that:

[Logroton] - (contains) --> [chlortalidone] (has_the_function) --> [diuretic function] (1)
But since we are in a logical formalism, and A and B => B, we therefore deduce, assuming that the truth of ( 1) is transmitted to that of (2), that:

[Logroton] -(has_the_function) --> [diuretic function] (2)
However, this is not true in the modelled domain because in the context of (1) the notion of function refers to the biochemical function of the active ingredient whereas in the context of (2) its meaning refers to the therapeutic function of the drug Logroton. Indeed, Logroton is an antihypertensive drug that carries the biochemical diuretic function in order to perform its therapeutic function of lowering blood pressure. This example clearly shows that the terms used by the formal system are not primitive notions as formalism would impose, but linguistic terms whose meaning is contextual, i.e. overdetermined by a point of view. The notion of function means by default the therapeutic function, but in the context of the active principle, this function means the physiological effect of the principle in question.

Thus, since the meaning of the formulas induced by the generative syntax of the formal system is not adequate to the contextual meaning induced by the interpretative operations of the domain, while being interpretable (since the symbolism of the formal systems is borrowed from natural language), the consequence is that the formal system, operationalized in a computer device whose computational capacities surpass those of our conscious cognitive operations, can lead to meaning formations corresponding to new knowledge in the domain that we could not anticipate, due to the inferiority of our conscious processor compared to the machine's.

The question thus became: how and in what way can a computing device produce meaning? By approaching this question from the point of view of cognitive technologies, this meant that the computational machine should no longer be considered as a means of modelling, but as a new type of support for the inscription of knowledge. Just as graphic writing is not a model of the world, and the world is not a book written in mathematical language (according to Galileo's beautiful metaphor), automatic formal systems revealed, thanks to the implementation of the reduced AI research programme, that they are not models of knowledge domains, but virtual operative and computational supports that convey knowledge and enable new knowledge to be constituted. It is this discovery that allowed the development of a critique of formalism in artificial intelligence [START_REF] Bachimont | Herméneutique matérielle et Artéfacture : des machines qui pensent aux machines qui donnent à penser[END_REF], the research programme of knowledge engineering and the elaboration of a critique of computational reason [START_REF] Bachimont | Arts et sciences du numérique : ingénierie des connaissances et critique de la raison computationnelle[END_REF].

Principles of semiotic engineering

What semiotic engineering seeks to specify is a principle of modelling that exploits the oblivion of logical formalism and a principle of effectivity that supplements the principle of computational effectivity [START_REF] Ferri | Science opérative et ingénierie sémiotique : des machines graphiques à la morphogenèse organique[END_REF]. We propose another principle of modelling, complementary to the principle of logical formalization, which we call the principle of phenomenographic representation. It should allow us to express the non-logical content of phenomenological knowledge, that is, the qualitative structure on which the nonlogical intuitive faculty is based, which was already recognized by Turing, in §11 of his PhD thesis [START_REF]Turing: Systems of Logic Based on Ordinals †[END_REF], as one of the two sources of mathematical reasoning.

Instead of having an abstraction of the linguistic content through logical formalization, we obtain an abstraction of the intuitive content through schematic representation. For this reason, semiotic engineering is not interested in the linguistic idiom as a vehicle of knowledge, but in the graphic symbol. The function of the graphic symbol is to compact this qualitative phenomenological structure in semiotic space so that it can be grasped synoptically by a human being who reads it.

Secondly, there must be a principle of effectivity. We call this principle the principle of operational iconicity. It is a principle of non-computational operational effectivity. Instead of exploiting a principle of computational effectivity, it is a matter of exploiting the mediation through which we access non-computational effectivity. This mediation is, in our view, operational iconicity [START_REF] Krämer | Why notational iconicity is a form of operational iconicity[END_REF]. Now, operational iconicity can be captured by a diagram insofar as a diagram is a semiotic machine, i.e. a machine that gives access to an operational content that is not reducible to a computational content.

1 . 8 3. 1 8 3. 2

 18182 Reduced artificial intelligence and semiotic engineering .............................................. 2 2. Peirce's phenomenology of knowledge: a methodological guide ................................... 4 2.1 Peirce's categories of being .................................................................................... 5 2.2 Reduced AI: purpose, method, principles ............................................................... 6 3. Limits of reduced AI and principles of semiotic engineering ....................................... The example of the concept of function in the context of medical knowledge modelling ..................................................................................................................... Principles of semiotic engineering .......................................................................... 9 1. Reduced artificial intelligence and semiotic engineering

From then on, the challenge of semiotic engineering is to develop a visual dictionary and grammar of practice, i.e. a visual semiotics of practical operations that cannot be reduced to computational operations [START_REF] Ferri | Science opérative et ingénierie sémiotique : des machines graphiques à la morphogenèse organique[END_REF].


Dr J Lee

Dr H Amari

Dr M Bahri

Prof. N D Browning

Dr B L Mehdi
email: b.l.mehdi@liverpool.ac.uk

Dr O Ersen

Dr C Xu

Dr Z Ruff

Prof. C P Grey

Dr Z Shen

Dr A Aguadero

Dr A Aguadero

Keywords: aluminium coating, Li-ion batteries, layered oxides, NMC811, Ni-rich cathodes

The Complex Role of Aluminium Contamination in Nickel-Rich Layered Oxide Cathodes for Lithium-Ion Batteries

Juhan Lee + , [a, f] Houari Amari + , [a, f] Mounib Bahri, [a, d] Zonghao Shen, [f, g] Chao Xu, [e, f] Zachary Ruff, [e, f] Clare P. Grey, [e, f] Ovidiu Ersen, [d] Ainara Aguadero, [f, g] Nigel D. Browning, [a, b, c, f] and B. Layla Mehdi* [a, f] A major challenge for lithium-ion batteries based on nickel-rich layered oxide cathodes is capacity fading. While chemomechanical degradation and/or structural transformation are widely considered responsible for degradation, a comprehensive understanding of this process is still not complete. For the stable performance of these cathode materials, aluminium (Al) plays a crucial role, not only as a current collector but also as substitutional element for the transition metals in the cathodes and a protective oxide coating (as Al 2 O 3 ). However, excess Al can be detrimental due to both its redox inactive nature in the cathode and the insulating nature of Al 2 O 3 . In this work, we report an analysis of the Al content in two different types of nickel-rich manganese cobalt oxide cathode materials after battery cycling. Our results indicate a significant thickening of Al-containing phases on the surface of the NMC811 electrode. Similar results are observed from commercial batteries (a mixture of NMC532 and LiMn 2 O 4 ) that were analysed before use and at the end of life, where Al-containing phases were found to increase significantly at surfaces and grain boundaries. Considering the detrimental effects of the excess Al in the nickel-rich cathodes, our observation of increased Al content via battery cycling is believed to bring a new perspective to the ongoing discussions regarding the capacity fading phenomenon of nickel-rich layered oxide materials as part of their complex degradation mechanisms.

The global demand for electrochemical energy storage systems has led to an increase in research into the development of advanced lithium-ion batteries (LIB). [1][2][3][4][5][6] From fulfilling individual needs for the small-scale storage of electricity in household gadgets, to providing larger-scale storage capacities in electric vehicles, LIBs have now become an intrinsic part of human activities, that promises to increase significantly in the future as we all strive for cleaner energy with a reduced environmental impact. [6,7] To increase the applications of LIBs and facilitate their incorporation into more aspects of modern society, current research goals aim to address current limitations by making LIBs cheaper, safer, more durable, and higher-performing both per unit mass and per unit volume. [2,8] Developments of these technologies must also bear in mind the need for an environmentally friendly circular economy, providing routes to battery recycling.

One of the materials that is currently being investigated to overcome the limited charge storage capacity (< 200 mAh/g) of conventional lithium-ion battery materials (e. g. LiMn 2 O 4 , LiFe-PO 4 , and LiCoO 2 cathodes), [9,10] is nickel-rich layered materials with high-energy densities such as LiNi x Co y Al z O 2 (NCA) and LiNi x Mn y Co z O 2 (NMC). [5,8] Despite the high intrinsic charge storage capacity in NMC (> 220 mAh/g) which can contribute to energy density approaching 800 Wh/kg in battery cells, a major challenge of nickel-rich materials is performance degradation, particularly in terms of capacity fading. [9,11,12] The primary origin of this fading with the number of charge-discharge cycles, has been explained by their vulnerable nature to chemo-mechanical degradation and detrimental structural transformation compared to their low nickel-containing alternatives. [12][13][14][15] Analysis of NMC under a wide variety of cycling conditions has revealed an extensive understanding of potential degradation effects. These include oxygen depletion, phase transformations to the spinel and rock-salt structures, transition metal dissolution, and side reactions at the cathode/electrolyte interface. [9,12,16,17] While comprehensive mechanisms for how these complex parameters mutually interact and govern overall performance degradation, surface coatings of nickel-rich layered particles such MgO and Al 2 O 3 have already been applied as effective solutions that enhance cyclic performance. [17][18][19] The improved capacity retention created by these coatings is widely believed to be enabled by suppressing both the undesired surface reactions and the structural and chemical transitions within the cathode material. [17,[19][20][21] Nonetheless, there are as yet few reports of the underlying mechanisms through which these coating layers interact with the active cathode particles. [17,20] Along with forming an oxide protection layer (Al 2 O 3 ) and substitution of electrochemically-active elements (e. g. NCA), aluminium (Al) chemistry in LIBs has also played a crucial role in current collectors within the cathode compartment. When being applied as a thin foil as current collectors for cathodes, metal Al alone is considered to be vulnerable to corrosions such as a hole or pitting formation. [22][23][24][25] Fortunately, the surface of the initial metal Al can be protected by an Al 2 O 3 passivation layer which can be naturally formed depending on the type of the electrolyte and its impurity content (with impurities such as H 2 O and HF being present). [24][25][26][27][28][29] Recent studies, however, show that even with an Al 2 O 3 layer, Al current collectors can be still exposed to chemical and anodic dissolution. [25,30] With the presence of HF, the Al 2 O 3 layer can be converted to more stable AlF 3 , meaning that LiPF 6 -based electrolytes may have a performance advantage as they generate HF through a decomposition reaction with water. [25,31] However, Zhang et al. reported that the Al current collector in a LiPF 6 -containing electrolyte is still susceptible to corrosion. [23] To understand the role that Al may play in controlling the capacity fading mechanism of nickel-rich layered oxide cathodes in LIBs, here we report the age-driven aluminium contamination process on NMC-type nickel-rich layered oxides by investigating the two different commercially available battery cathodes. Through atomic scale scanning transmission electron microscopy (STEM) observations coupled with time-offlight secondary ion mass spectrometry (ToF-SIMS) we find that the Al in the system migrates during cycling to interfaces and defects, in some cases leading to nanoscale intergranular films being formed. As such films are known to have a deleterious effect on battery performance, here we discuss the correlation between the observed aluminium contamination to the surface layers on the nickel rich cathodes and the evolution of the properties of the system with cycling history.

While the structure of the commercially available LIBs varies from a single-stack coin cell to multi-stack pouch or cylindrical cells, the layout inside the batteries is almost identical; consisting of a cathode (or positive electrode), an anode (or negative electrode), a porous separator, and current collectors (schematically described in Figure 1A). In the case of commercial LIBs with NMC cathodes, graphite is generally the anode material, with Al and copper (Cu) current collectors in the cathode and anode, respectively. The Targray NMC811 cathode particles used in this work have a typical morphology of spherical secondary particles consisting of primary particles [12,15,32] as presented by scanning electron microscopy (SEM) (see also Supporting Information, Figure S1); the primary particles within a size of ca. 0.1-0.2 μm are densely packed, forming spherical secondary particles of a size of about 4-20 μm (Figure S1A-B).

The average capacity retention performance of the NMC811 cathodes from two LIB coin cells is shown in Figure 1B. To investigate the origin of the capacity fade in these cathode materials, the samples were collected after 1 and 300 battery ageing cycles at 4.2 V and subsequently reassembled in lithium half-cells and delithiated to the same charged state (4.3 V vs. Li). Then, we examined several secondary particles from the sample after 300 cycles by continuous cross-sectioning via a focused-ion beam, FIB. As demonstrated by one of these examples (see also Supporting Information, Figure S1C), we have found no visible sign of crack formation in the investigated samples. These results are consistent with our previous study by in situ XRD and imply that chemo-mechanical degradation is not a governing factor for the capacity fading in these materials. [33] A rather convincing explanation for at least one source of capacity fade (of the cathode) is the surface reconstruction on the edge of the NMC811 particle from the initial layered rhombohedral (R � 3m, Figure 1C) to face-centred cubic (Fm � 3m; ) Figure1D structure. The formation of a surface rocksalt structure orthogonal to Li diffusion channels can pin the lattice planes of the R � 3m layered structure and lead to a limited maximum state-of-charge for lithium deintercalation. [33] To investigate further avenues for performance degradation in nickel-rich layered oxides materials, three NMC811 electrodes at different ageing conditions were examined for ToF-SIMS analysis: the pristine Targray electrode, and the Targray cathodes after 1 and 300 cycles at 4.2 V in a full-cell configuration. In a negative acquisition mode, Al was found on a large area of the surface (250 μm × 250 μm) of all samples as evidenced by Al + , AlO À , AlO 2 À , and AlF 4 À fragments (Supporting Information, Figure S2-3). These fragments can all be identified as components that could originate from the Al 2 O 3 NMC coatings, these coatings reacting with HF to give AlF 3 , or the Al current collector and its Al 2 O 3 natural oxide. [21,[24][25][26][34][35][36] The formation of AlF 3 or Al 2 O 3 may have also been enabled by additional sources of Al in the electrolyte (as a poison or an additive). However, the concentration of Al in the pristine electrolyte was below the detection limit of our inductively coupled plasma atomic emission spectroscopy (ICP-OES) measurement (< 3.5 μg/L or < 175 ng in the 50 μl of electrolyte used per cell); details in Supporting Information Table S1. Taking the upper-bound of the potential Al contamination in the pristine electrolyte, this would correspond to < 3.0 × 10 À 5 ratio of Al to

Batteries & Supercaps transition metals in the NMC811 cathode and would not likely be challenging to quantify on a bulk scale by the STEM-EDX measurements discussed later. A more significant source of Al is corrosion from the Al-current collector (at the cathode). ICP-OES measurements have shown Al μg-level deposits on the anode after cycling, indicating that there is significant Al dissolution, migration and deposition in these cells (Supporting Information, Figure S6). We also note that significant deposits of nickel, manganese and cobalt also were measured at the anode in agreement with other studies on NMC cathodes. [37,38] The normalised ToF-SIMS depth profiles no deeper than ~500 nm from the surface obtained via Cs + sputtering (Figure 2A, point-to-point normalised to the total counts) show a general tendency in all samples that the AlO À signals increase at the beginning of the sputtering and start decreasing after reaching the peak values. The same trend was observed for the AlF 4 À signal from the sample after 300 cycles while the monotonous weakening of the AlF 4 À signal can be perceived for the pristine electrode and the sample after the 1 st cycle. These tendencies indicate the presence of an Al and F containing layer on the surface of the secondary NMC particles and Al and O containing layer underneath. These results are consistent with the related Li-ion battery studies that AlF 3 layers can be formed on the Al 2 O 3 layer through a reaction with HF. [21,25,26] Based on the ToF-SIMS data for the pristine electrode, the possible structure of the NMC primary particle was schematically illustrated in Figure 2B; the illustration is not precisely scaled with the actual size of the phases, the size of the primary and secondary particles are roughly estimated based on the SEM images (Supporting Information, Figure S1).

As the cycle number increases (Figure 2A), the signal intensities for AlF 4

À and AlO À gradually enhance, implying that Al is introduced to the NMC particles from additional Al sources. While the presence of these fragments is consistent with other related studies regarding Al 2 O 3 and AlF 3 passivation layers, [18,21,[24][25][26] the increased Al content in Nickel-rich cathodes after battery ageing processes has not been reported so far. Also, we found that the peak of AlO À signal shifts to higher sputtering cycles at higher battery cycling numbers while no such shift was observed for the AlF 4 À signal (see also Supporting Information, Figure S2B). The shift of AlO À signal may originate in the thickening of the cathode electrolyte interface (CEI) consisting of species like LiF, Li 2 CO 3 , and Li x PO y F z . [39][40][41][42] The CEI layer can be effectively investigated based on F containing signals such as Li 2 F 3 À and LiF 2 À (Figure 2C, see also Supporting Information, Figure S3). [39] The profiles of these signals, however, did exhibit only a fraction of a shift as compared to the AlO À profile. Therefore, the peak shift from Batteries & Supercaps the AlO À is considered to be caused more likely due to the thickening of the Al-containing layer rather than due to the growth of the CEI layer.

The cathode materials described above have also been analysed by Z-contrast imaging [40] and energy dispersive X-ray spectroscopy (EDX) 41 in the scanning transmission electron microscope (STEM). The ~1 nm spatial resolution of the Zcontrast images, which allow variations in mass-thickness to be easily observed, and the EDX spectra, which allow the composition variations to be quantified to ~2-5 % accuracy, permit the locations of the Al phases observed by ToF-SIMS to be identified within the microstructure of the cathode materials. To investigate this spatial distribution, we examined 5 random areas from the various primary particles in the size of 0.1-2.0 μm for each sample via STEM-EDX. The elemental signal mapping data (Figure 3A) indicates that particles in all samples (pristine NMC811 powder, electrodes after 1 and 300 cycles) contain O, Mn, Co and Ni, which are core elements of the NMC cathode. Consistent with the ToF-SIMS, there is a trace level of Al in the pristine electrode, [21] and an increased concentration of Al distributed within and upon the cathode materials (Supporting Information, Figure S4).

A further detailed demonstration of the statistical analysis, the elemental composition of Ni, Mn, Co, and Al is shown in Figure 3B (see also Supporting Information for the entire elemental composition containing oxygen, Figure S5A). The analysed data shows a relatively homogeneous stoichiometry of Ni, Mn, and Co (ca. 8 : 1 : 1) for all investigated samples as also evidenced by uniformly distributed mapping signals (see also Supporting Information, Figure S4B). Interestingly, the distribution of the higher Al content (Figure 3B, inset) after an increased number of battery cycles suggests that Al is present not only at the outer shell of the secondary particles but also in the primary particles beneath the surface (see also Supporting Information for the detailed evidence of Al, Figure S4C-F).

As shown in Figure 1 and discussed earlier in this paper, the initial layered structure of NMC can be converted into a spinel and/or rock salt-like structure when the NMC cathode undergoes long-term electrochemical cycling. [14,33,44] Interestingly, [33] the samples used in this work did not undergo such major structural transformations; instead, a partial transition from the layered structure to the face-centred cubic structure was observed at the surface layer after 300 cycles at the cell voltage of 4.2 V. This surface-reconstructed area is shown in ADF-STEM images Figure 3C to exist over no more than a few unit cells at Batteries & Supercaps the particle surfaces associated with a surface covering of alumina. Based on the crystal structure and the distribution of Al content (Figure 3A, see also Supporting Information, Figure S6B), it seems unlikely that the high Al content after cycling is contained only within the rock-salt structure, but rather that the alumina surface layer controls the formation of this surface phase. [45,46] Given the nature of the cathode materials, i. e. polycrystalline, a possible location for the Al-containing phase is along the grain boundaries between the primary particles. One means to be able to see the Al presence at grain boundaries would be to further cycle the materials and increase the Al content even further. Unfortunately, this was not possible with the raw materials available for the controlled cycling study shown above, end of life came shortly after the current number of cycles. However, we can access the distribution of Al after extended cycling by using the STEM-EDX method to characterise highly aged commercial batteries which consist of similar cathode materials. Figure 4 shows EDX maps obtained from 1 st generation Nissan Leaf batteries. The first set of maps is from a pristine battery cathode from a quality control (QC) failed cell, while the second set of maps is obtained from an end-of-life cell that had been driven in a Nissan Leaf for many years. While these battery materials do not have the controlled history of the samples shown in Figure 1-3, all samples were dismantled in glove boxes and used powders from the same source (in this case there are additional variables, as in the first generation of Nissan Leaf batteries used a mixture of LMO and Al doped NMC (532) for its cathode materials). Of key importance in these results is the observation of a more uniform distribution of Al at low-levels in the pristine material, that is transformed into a higher concentration at specific locations in the end-of-life battery. The large deposits of Al-containing phases seem to correspond to "pockets" at major intersections between the grains of the primary cathode particles. However, such large Al agglomerates were not observed in the case of the NMC811 in the initial 300 cycles (probably due to the higher starting Al content in these real-world materials). A likely scenario here is that the amount of Al 2 O 3 in the grain boundary is not sufficient to be quantified by EDX (anything less than ~2 % will likely be below the noise threshold) for the latter case. Nonetheless, the similarity in the pristine materials and the extension of the same behaviour in both these samples indicates that the mobility of the Alcontaining phases in the cathode is a real effect that must be considered for degradation and given that these are now distinct phases that are present, also for the recycling of LIBs.

Batteries & Supercaps

While the ToF-SIMS and STEM-EDX analysis evidently indicate the increasing Al content during ageing/degradation, the exact origin of Al is unclear at this stage. The possible sources of Al could be Al 2 O 3 surface layers on the primary cathode particles and the Al current collector. Based on the previous studies regarding the Al current collector in LIBs, [23,25,30,[24][25][26][27][28][29] perhaps the most obvious route is the dissolution of the current collector to the electrolyte (see also Supporting Information, Figure S6), but identification of the exact mechanism will be the subject of future work. While the origin of the excess Al may not be easily identifiable, there is no doubt from the different sets of results that it is present upon cycling, and as such we can speculate as to its role in degradation processes. Considering the electrically insulating feature and redox inactive nature of Al 2 O 3 for the lithium battery operations, the thickness of the protective aluminium oxide layer has been shown to be optimised at a value of ~2 nm. [47,48] For instance, Zhu et al. systematically investigated the influence of Al 2 O 3 coating layer on NMC811 via atomic layer deposition and observed a detrimental effect of the coating layer to lithium storage capacity when the thickness exceeds 5 nm. [48] Hence, only the adequate amount of Al on the coating layer seems to be beneficial, which can help with the diffusion of Li into the NMC while at the same time suppressing the formation of a CEI layer, improving cyclability of the material. [47] In addition, as discussed here, there also appears to be a decrease in the formation of secondary phases during cycling when Al is present, further decreasing the capacity fading of the system. The presence of the Al-containing phase at grain boundaries may offer another benefit. Intergranular films have for many years been used with polycrystalline ceramic oxides and nitrides to reduce crack propagation and improve overall mechanical properties. [49] The lack of chemo-mechanical deformation in these samples may be an indication of this effect. The grain boundary effect is also supported by the presence of larger Al deposits in the end-of-life commercial battery. It is known that diffusion typically takes place in intergranular films resulting in large deposits at the triple points in the grain boundary networks. [50] The continual supply of Al from other parts of the battery structure may turn the advantageous Al 2 O 3 interface layer that helps suppress capacity fading at the start of life into a process that accelerates it as the battery continues to age and these phases increase beyond the critical thickness.

To conclude, we have investigated the role of Al contamination on the battery ageing process using ToF-SIMS and STEM-EDX analysis. Pristine NMC 811 samples possessing a sub- Batteries & Supercaps nm coating of Al 2 O 3 are found to be increasingly covered with thicker layers of Al-containing phases as the cycling and ageing process proceeds -evidence suggests the thickening is an increase in an Al-containing phase on the primary particle grain boundaries with a relatively constant and thin AlF 3 or aluminium oxyfluoride layer on top. While the presence of a small amount of aluminium in the cathodes is widely believed to enhance the stability of nickel-rich layer oxides, detrimental effects are also expected for an excessive amount of Al 2 O 3 and the incorporation of Al in the NMC structure. Our results, therefore, suggest that at some point during the ageing process, the increasing level of Al-containing phases may switch from preventing capacity fading to, perhaps, enhancing it. Given that intergranular films can affect both the mechanical, electrical and chemical properties of polycrystalline systems, determining which effect is predominant under specific conditions will require further study, including the detailed roles of Al contamination in the nickel-rich layered oxides with other reported phenomena such as oxygen depletion, phase transition, and transition metal dissolution.

Experimental Section Materials

The graphite electrodes and polycrystalline NMC811 are fabricated and provided by the Argonne National Laboratory CAMP facility. Briefly, the NMC cathode (batch code A-C020) is composed of 90 wt % NMC811 (Targray), 5 wt % carbon black (Timcal C45), 5 wt % PVDF binder (Solvay 5130), and the graphite electrode consists of 91.83 wt % graphite powder (Hitachi MagE3), 0.17 wt % oxalic acid, 6 wt % PVDF binder (Kureha 9300), and 2 wt % carbon black (Timcal C45). These laminate electrodes were then punched into 14 mm (NMC811 cathode) and 15 mm (graphite electrode) circular disks, respectively. Then, these circular electrodes were dried further at 120 °C for 12 h under dynamic vacuum (~10-2 mbar) in Büchi oven and transferred to glovebox without airexposure. As electrolytes, 1 M LiPF 6 , EC/EMC 3/7 (LP57, SoulBrain MI, USA) was used in this work, and the separator was Celgard 3501. The Celgard separator was punched into 16 mm disks, washed in ethanol three times and dried at 50 °C under vacuum.

The pristine battery material was obtained from a first generation Nissan Leaf battery pack that had undergone QC fail (not because of the material quality but due to the mechanical failure in the contacts) and was never cycled. The end-of-life battery material was obtained from a first generation Nissan Leaf battery pack that was used in a road vehicle for many years. All samples were extracted using a glove box to ensure no atmospheric degradation processes took place.

Battery assembly and cycling

Long-term cyclability were all performed in NMC/graphite full-cells using 2032 coin cells (Cambridge Energy Solution). Coin-cells were assembled in an Ar-atmosphere (O 2 < 1ppm, H 2 O < 1 ppm) glovebox. Full cells were composed of a 14 mm NMC cathode, 16 mm separator and 15 mm graphite anode, and 50 μL electrolyte was added to each coin cell. The electrolyte used in polycrystalline NMC/graphite full-cells was LP57. The cells were aged at a rate of C/2 (calculated based on a reversible capacity of 200 mAh g À 1 of NMC cathode) between 4.2 V and 2.5 V at room temperature (20 � 1 °C) using CCCV (constant current constant voltage) charging and CC (constant current) discharging protocol. CCCV charging was composed of a constant current step followed by a constant voltage hold at the upper cut-off voltage, i. e. 4.2 V, until the current dropped below the value of C/20. Prior to the ageing cycles, one tap charge process and two formation cycles were applied. Tap charge was performed by holding the cells at 1.5 V for 15 min, followed by a long rest of 6 h to allow cells to be fully wetted. Formation cycles were conducted at C/20 rate also using CCCV charging (current limit of the CV step is C/40) and CC discharging protocol. For post-mortem samples at certain voltage or state-of-charge after extended ageing, full-cells were disassembled inside a glovebox.

Material characterisation

All NMC811 samples were stored and prepared in the Ar glove box. The morphology of NMC811 samples was investigated by a JEOL JSM 7001F field emission scanning microscope (FE-SEM) at an acceleration voltage of 15 kV and SEM-FIB (FEI Helios Nanolab 600i). The dark-field scanning transmission electron images (DF-STEM) were taken with an aberration-corrected JEOL JEM-2100 operated at 200 kV. With the latter setup, EDX data was obtained by EDAX Octane T Optima windowless 60 mm 2 SDD EDX detector with a dwell time of 0.1 μs. For STEM and EDX analysis, the samples were crushed and placed on lacey-carbon-coated Au grids. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), a SIMS 5 spectrometer (IONTOF GmbH, Münster, Germany), was applied for the chemical analysis. The analysis was performed in the high current bunch mode (HCBM) with a 25 keV Bi + primary beam over an area of 250 μm × 250 μm for all NMC samples. For sputtering, a 1 keV Cs + sputtering beam was applied with a raster area of 500 μm × 500 μm. The beam current of Cs + was consistent during sputtering for all three samples. Additionally, all the samples were mounted in an Ar-filled glovebox and were transferred into the instrument within a vacuum suitcase which was opened in the loadlock chamber until the pressure was lower than 10 À 5 mbar in order to avoid the influence from ambient environment.

Figure 1 .

 1 Figure 1. A) Schematic illustration of a lithium-ion battery cell. For simplicity, the binding material is not illustrated. However, in our study, we applied PVDF binder for NMC811 cathodes. B) Capacity fading of NMC811 Targray cathodes. C-D) ADF-STEM images of the NMC811 Targray particle. C) Layered rhombohedral structure of the pristine electrode in [001] zone axis. The scale in the main image is 2 nm, and 0.5 nm in the inset on the right. D) Rock salt is formed orthogonal to the lithium diffusion channels of the layered structure.

Figure 2 .

 2 Figure 2. ToF-SIMS data and schematic illustration of NMC811 Targray electrode. A) Depth profiles for AlO À and AlF 4 À fragments obtained by Cs + sputtering for the pristine NMC electrode and the NMC Targray cathode after 1 and 300 cycles at 4.2 V in a full cell. The intensity is point-to-point normalised to the total counts. B) Schematic illustration of the cathode compartment in a full cell, a secondary particle with Al 2 O 3 and AlF 3 coating layers, and the detailed illustration for the pristine and the aged sample; from left to right. C) Depth profiles for AlO À and Li 2 F 3 À fragments.

Figure 3 .

 3 Figure 3. STEM-EDX analysis of the pristine NMC811 Targray powder and NMC811 Targray cathodes after 1 and 300 cycles at 4.2 V in a full cell. A) Elemental EDX mapping based on signal integral. B) Statistical elemental composition based on EDX analysis. C) ADF-STEM image of the particle after 300 cycles presented in (A) in the bottom row. Insets show ADF-STEM atomic resolution images for the areas labelled as left, middle, and right; the unfiltered images in the top row and FFT-filtered images in the bottom row.

Figure 4 .

 4 Figure 4. STEM-EDX maps showing the presence and distribution of Al in A) a pristine and B) an end-of-life cathode from a first generation Nissan leaf battery. Over the extended cycling of the battery, Al containing phases appear to increase and form primarily at grain boundary triple pockets. Care was taken to acquire samples away from the Al current collector to avoid contamination artifacts, and all sample preparation took place in a glove box. The formation of large Al phases has an effect on degradation, recycling and second life applications of LIBs. The scale bar is 0.5 and 2.0 μm for the pristine and the end of life electrode, respectively.

Batteries & Supercaps 2021, 4, 1 -9 www.batteries-supercaps.org © 2021 The Authors. Batteries & Supercaps published by Wiley-VCH GmbH These are not the final page numbers! ��

Acknowledgements

We would like to thank Mathew Bilton and Adam Papworth for assistance with FIB/STEM experiments. This work was supported by the Faraday Institution through awards FIRG001 "Degradation" and FIRG005 "ReLiB".

Conflict of Interest

The authors declare no conflict of interest.

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The role of Al: We report that the level of aluminium contamination on nickel-rich manganese cobalt oxide increases as a function of battery cycles; in particular, the Al-containing phases were observed at surfaces and grain boundaries. This observation of increased Al content can bring new insights into the ongoing discussions concerning the capacity fading phenomenon of nickel-rich layered oxide materials in lithium-ion batteries.