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The influence of cobalt substitution on the local structural changes around Co atoms in the layered lithium nitridocobaltates Li(3-2x)Co(x)N for 0.05 ≤ x ≤ 0.44 is investigated using Co K-edge X-ray absorption spectroscopy (EXAFS and XANES). The Co-N bond length in Li(3-2x)Co(x)N compounds is obtained vs x by performing EXAFS fitting and found to be shorter (1.80 Å) than for x = 0 (Li3N), and its value does not change with x. A comparison of EXAFS data with XRD results is discussed. We show that the continuous decrease of interlayer distance versus Co content (x), described from XRD data, accounts for an average of the Co-N and Li-N distances, weighted by the number of these bond lengths. In addition, the present work supports the proposal that the Li1b-N bonds contract with x due to a significant increase of Coulombic attractive forces locally induced by the progressive Li(+)/Co(2+) substitution. XRD studies suggested that divalent Co ions bond to two nitrogen in Li(3-2x)Co(x)N. Although additional works are still needed to prove its valence, the present XAFS findings complements the local structure found by XRD, in good accord with the electrochemical properties previously reported.

The SEI (Solid Electrolyte Interphase) at the surface of electrodes in lithium-ion batteries is composed of various lithium compounds, organic or mineral, which have a direct impact on cycling performance. The main lithium species constituting the SEI and selected in this study are lithium fluoride LiF, lithium carbonate Li2CO3, lithium hydroxide LiOH, lithium oxide Li2O, lithium methoxide LiOCH3 and lithium ethoxide LiOC2H5. Their solubilities were determined in ethylene, propylene, dimethyl, diethyl and vinylene carbonates (EC, PC, DMC, DEC and VC) and in one of their mixtures commonly used in lithium-ion batteries (EC/PC/3DMC) by mean of atomic absorption spectroscopy (AAS). These solutions were also investigated by EIS (Electrochemical Impedance Spectroscopy) and conductimetry measurements. Results show that while solubilization properties differ between LiF and other lithium compounds considered, their association pattern in solution is identical and solutions are mainly constituted of quadrupolar aggregates.

Lithium-ion batteries for space applications, such as satellites, are subjected to cosmic radiations, in particular, γ-irradiation. In this study, the effects of this radiation on electrolytes and their components used in the lithium-ion batteries are investigated. The conductivity and viscosity of the samples have been measured before and after the irradiation. The modifications are evaluated by spectral analyses such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy ( 1 H and 13 C NMR), solid phase microextraction-gas chromatography (SPME-GC) and gas chromatography–mass spectroscopy (GC–MS). The experimental results show that only the samples containing vinylene carbonate and/or the lithium salt LiPF 6 are degraded by γ-radiation.

The solubility of lithium fluoride has so far never been studied in alkylcarbonate solvents. These data is essential to understand the behavior of this salt in solution, in particular in the field of lithium-ion batteries. The solubility of lithium fluoride (LiF) was measured at various temperatures in propylene carbonate (PC), ethylene carbonate (EC) and dimethyl carbonate (DMC) by atomic absorption spectroscopy. The LiF free enthalpy, enthalpy and entropy of dissolution in these solvents were deduced from the results. The solubility of LiF differs significantly with the nature of the solvent, EC being by far the most solubilizing media. The high solubilizing power of EC towards LiF cannot be explain by any of the physico-chemical properties of the solvent, but by an entropy-driven phenomenon. The solubilities of LiF in water–alkylcarbonates mixtures were determined by conductimetry at several temperatures leading to the corresponding LiF thermodynamic properties in these media. Results are discussed and compared to those obtained by atomic absorption measurements. Finally, a scheme representing the different stages for the dissolution of LiF in alkylcarbonates is proposed.

Lithium cobalt nitrides Li3−2xCoxN (0.1 ≤ x ≤ 0.44) have been prepared and investigated as negative electrode in the 1/0.02 V potential window. The evolution of the unit cell parameters and unit cell volume with the Co content show a solid solution behaviour. Whatever the Co content, all these nitrides are electroactive with a single step around 0.6 V/0.7 V for the discharge and charge processes, respectively. The electrochemical behaviour observed is typical of a Li intercalation compound and involves the Co2+/Co+ redox couple in the interlayer plane combined with the reversible accommodation of Li+ ions in the cation vacancies located in Li2N− layers. XRD experiments performed after discharge, charge and cycling tests clearly indicate the hexagonal layered structure of the host lattice is maintained. This intercalation process explains the excellent capacity retention found after 50 cycles. A specific capacity of 180 mAh g−1 at C/20 and 130 mAh g−1 at C/5 rate (100 mA cm−2) is achieved for Li2.23Co0.39N. ac impedance measurements have allowed to characterize the kinetics of the reaction.

Redox shuttle electrolyte additives have been suggested as a possible mean of internal overcharge protection of secondary lithium-ion batteries. TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) is one of these redox shuttles for overcharge protection of 3 V class Li-ion cells. The electrochemical reversibility and the diffusion coefficient of this molecule has been evaluated by mean of cyclic voltammetry. The redox shuttle voltage was found to be 3.5 V versus Li/Li + and D = cm 2 s −1 . The electrochemical stability of TEMPO in different overcharging conditions has been evaluated by long-term cycling using Li/Li 4 Ti 5 O 12 cells. Results show that the TEMPO redox system does not act as an ideal shuttle. When dissolved in the electrolyte at 0.5 M, this additive is able to level off the cell potential at 3.5 V for a long period at low overcharging current ( C /200 to C /50). Nevertheless, it appears that the cell capacity fades drastically at the first cycles and with time. This phenomenon is probably related to the stability of the oxidized and reduced form of the TEMPO molecule.

Based on the voltammetric behaviour of a series of halogen-substituted dimethoxybenzene in 1 M LiPF 6 /EC:DEC electrolyte, 2,5-difluoro-1,4-dimethoxybenzene (F 2 DMB) was selected and tested as an electrolyte additive for overcharge protection of Li/Li 4 Ti 5 O 12 cell. From the galvanostatic study of the cells at different overcharge current ( C /20, C /50, C /100 and C /200) in the presence of F 2 DMB, it was found that the shuttle additive can be adsorbed at the cathode surface and form a dense layer which prevents the intercalation of Li + ion in the positive electrode. At low overcharge current ( C /200 rate) the voltage of the cell levelled off at the oxidation potential of the shuttle molecule for more than 50 cycles, but at higher charge rates ( C /50 and C /100), the voltage of the cell was levelled off for only 16 cycles. The reason is that the F 2 DMB molecules remaining in solution after the formation of the layer at the cathode cannot carry the current even at charge rates as low as C /100.

Sn-based composite materials were synthetized by a conventional meltquenching method, and studied by X-ray diffraction, electrochemistry and in situ 119Sn Mosssbauer spectroscopy. Tin was dispersed ex situ into a matrix formed from B2O3:P2O5. XRD and 119Sn Mossbauer spectroscopy show the formation of an interface between the active species (Sn0) and the matrix. This amorphous interface acts as a “buffer-zone” which compensates volume changes during the tin-lithium alloy formation and avoids aggregation of tin particles.

Tin–graphite materials were prepared by chemical reduction of SnCl 4 by t -BuONa-activated NaH. TEM imaging showed that the crude material is composed of an amorphous organic matrix containing tin present either as nanosized particles deposited on the graphite surface or as free aggregates. Subsequent washings with ethanol and water allow removal of side products as well as most part of the organic matrix. Electrochemical insertion of lithium occurred in graphite and in tin. The initial reversible massic capacity of 630 mAh g −1 decayed to a stable value of 415 mAh g −1 after 12 cycles. This capacity value was lower than the expected maximum one of 650 mAh g −1 corresponding to a Sn/12C molar composition and assuming the formation of LiC 6 and Li 22 Sn 5 . Even if this massic capacity is not much improved by comparison with that of graphite, it must be pointed out that the volume capacity of this graphite/Sn material is much larger (2137 mAh cm −3 ) than that corresponding to graphite (837 mAh cm −3 ). It was hypothesized that the part of tin bound to graphite could be responsible for the stable reversible capacity. To the contrary, graphite unsupported tin aggregates would contribute to the observed gradual decline in the storage capacity. Therefore, the improvement in cycleability, compared to that of massive metals, could be attributed both to the nanoscale dimension of the metal particles and to interactions between graphite and metal the nature of which remaining to be precised.

For the search of new negative electrodes of Li-ion batteries, a low-temperature method has been developed for the preparation of nanoscale antimony particles which uses an alkoxide-activated sodium hydride as reducing agent of antimony pentachloride. X-ray diffraction and TEM studies confirm the obtaining of amorphous Sb nanoparticles dispersed in an organic matrix. 121Sb Mossbauer spectroscopy gives evidence for the occurrence of interactions between antimony and the matrix. These interactions are modified by the washing treatments.

There is a renewal of interest in the use of metals that are capable of alloying with lithium as negative-electrode materials for lithium-ion batteries. These metals can supply larger capacities than graphite but their main disadvantage consists in their very limited cycle life. Indeed, they present considerable volume variations during alloying, which lead to a mechanical degradation of the electrode. The concept of an active phase stabilizing matrix was introduced. We propose in this study to associate a metal able to alloy lithium to graphite by using new preparation methods involving graphite intercalation compounds (GICs) as precursors. In one case, antimony pentachloride SbCl5 was reduced by the stage I KC8 GIC. In another case, C12SbCl5 and C24SbCl5 GICs were reduced either by gaseous caesium or by activated sodium hydride NaH. Actually, these methods led to the attention of antimony-based graphite composites in which antimony particles are deposited on the surface and edges of graphite layers or embedded in an organic matrix. Both morphological and structural characteristics of such composites were studied by transmission electron microscopy. Examination of their electrochemical properties as regards lithium insertion showed that they present interesting performances because the reversible capacity is increased by comparison with that of pure graphite and the stability of the metal is preserved throughout the cycling. The combination of graphite and antimony prevents the metal against cracking and pulverization that occur generally during alloying/dealloying cycles. Antimony-graphite composites prepared via SbCl5 reduction by KC8, via C12SbCl5 reduction by gaseous caesium or via C24SbCl5 reduction by activated NaH display improved reversible capacities of 420, 490 and 440 mAh g−1, respectively.

Preparation of antimony-based graphite composite using a graphite intercalation compound as precursor was described. A C 12 SbCl 5 graphite intercalation compound was reduced by caesium in the vapor phase at 70 °C. The resulting compound was composed of antimony particles deposited on a graphite matrix. Used as negative-electrode material for lithium-ion rechargeable cells, this composite presented not only an improved storage capacity (490 mAh g −1 between 0 and 2 V versus Li + /Li) by comparison with free graphite but also enhanced dimensional stability of lithium–antimony alloys.

An algorithm is proposed for calculating the energy of ion-dipole interactions in concentrated organic electrolytes. The ion-dipole interactions increase with increasing salt concentration and must be taken into account when the activation energy for the conductivity is calculated. In this case, the contribution of ion-dipole interactions to the activation energy for this transport process is of the same order of magnitude as the contribution of ion-ion interactions. The ion-dipole interaction energy was calculated for a cell of eight ions, alternatingly anions and cations, placed on the vertices of an expanded cubic lattice whose parameter is related to the mean interionic distance (pseudolattice theory). The solvent dipoles were introduced randomly into the cell by assuming a randomness compacity of 0.58. The energy of the dipole assembly in the cell was minimized by using a Newton-Raphson numerical method. The dielectric field gradient around ions was taken into account by a distance parameter and a dielectric constant of epsilon = 3 at the surfaces of the ions. A fair agreement between experimental and calculated activation energy has been found for systems composed of gamma-butyrolactone (BL) as solvent and lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as salts.

A nickel hydroxide electrode and a commercial battery have been studied by a new and contact-less impedance method, based on Foucault’s eddy currents, with the aim of determining their state of charge. Four different current line distributions have been employed and the impedance versus time graphs obtained show a linear variation of this impedance during charge and discharge for all configurations. This new method allows the determination of the state of charge and, furthermore some “artifacts” obvious on these graphs may be useful to detect a deterioration of the studied material.

Thermodynamic data on liquid mixtures are usually expressed as excess quantities and analysed with the Redlich–Kister equation. Excess molar volume, excess viscosity, excess dielectric constant, and excess Gibbs energy of activation flow are calculated for γ-butyrolactone (BL) and dimethylcarbonate (DMC) mixtures at T=298.15 K and atmospheric pressure over the complete composition range. All these excess thermodynamics functions shows that DMC is less associated than BL and the interaction between pairs of like molecules is stronger than between pairs of unlike molecules.

The deviation in excess thermodynamic parameters such as molar volume (VE ), viscosity ( ηE), dielectric constant (ϵE ), Gibbs energy of activation of the viscous flow (G * E ) and surface tension ( γE) have been determined for propylene carbonate and 2,2,2-trifluoroethyl methyl carbonate (TFMC) mixtures atT = 298.15 K and for ethylene carbonate and TEMC mixtures at T = 313.15 K. All quantities were plotted against mole fraction over the whole concentration range. Polynomial regressions have been fitted with the results. The strength and the nature of the interactions between like and unlike components have been discussed.

Viscosity and conductivity properties of Li-salts (lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium bis-(trifluoromethylsulfone)-imide (LiTFSI)) dissolved in γ-butyrolactone (BL) have been investigated. The B- and D-coefficients of the Jones–Dole (JD) equation for the relative viscosity of concentrated electrolyte solutions (concentration: C=0.1–1.5 M): ηr=1+AC1/2+BC+DC2, have been determined as a function of the temperature. The B-coefficient is linked to the hydrodynamic volume of the solute and remains constant within the temperature range investigated (25–55 °C). The D-coefficient, which originates mainly from long-range coulombic ion–ion interactions, is a reciprocal function of the temperature. The variations of the molar conductivity (Λ) with C follow the cube root law Λ=Λ0′−S′C1/3 issued from quasi-lattice theory of electrolyte solutions. From the Walden product W=Λη which does not vary with C and the JD equation, the bell shape of the conductivity–concentration relationship is explained and it is shown that the concentration in salt at the maximum of conductivity is linked to the D-coefficient. Raman spectroscopy has been used as an additional tool to investigate ion pairing in BL. Ions pairs have been evidenced for LiClO4 solutions in BL but not for LiPF6. As little variations occur for the ions pairs dissociation coefficient when the salt concentration is increased, the cube root law remains valid, at least in the concentration range investigated.

A semi theoretical explanation of the appearance of a second plateau during the discharge of overcharged nickel oxyhydroxide electrodes (NOHE) is proposed, based on transmission line models of the charge–discharge processes of the active matter. The model takes into account the double electronic and protonic conduction involved in nickel II α and β or nickel III β and γ phases: electrons and protons reach the transformation front inside the matter through the less resistive paths. The secondary plateau may occur when a resistive layer of β(II) isolates the transformation front from the nickel electron sink.

The electrochemical intercalation of lithium ions into graphite was studied in various electrolytes. The first cycle is accompanied by the irreversible process attributed to the formation of a passivating layer. The reduction of Cl–EC and EC begins at potentials equal to 1.7 and 0.9 V vs. Li+/Li, respectively. The electrochemical behaviour is considerably affected by the nature of the salt. Contrary to LiBF4, a good cycleability is obtained with LiClO4 and LiAsF6.

Lithium hexafluorophosphate (LiPF 6 ) has been synthesized using commercial hexafluorophosphoric acid (HPF 6 ) as starting material. The neutralization of this acid monitored by conductimetry by lithium hydroxide in aqueous, alcoholic and acetonitrile media gives LiPF 6 with yields of 42, 35 and 61% respectively. This salt may also be prepared by neutralizing similarly lithium hydroxide (LiOH) by pyridinium hexafluorophosphate (C 5 H 5 NHPF 6 ) obtained by reaction from equimolar amounts of pyridine and HPF 6 in alcoholic media (yield about 90%). From C 5 H 5 NHPF 6 a new synthesis leads to LiPF 6 in two steps. First the reaction of C 5 H 5 NHPF 6 with ROLi (R = CH 3 , C 2 H 5 ) in methyl or ethyl alcohol, acetonitrile and tetrahydrofuran media or with RLi (R = C 4 H 9 , tert -butyl) in pentane or hexane, gives lithium pyridinium hexafluorophosphate Li(C 5 H 5 N)PF 6 in about 95% yield. Heating this at 30–50 °C under vacuum gives LiPF 6 with a purity determined by lithium titration of about 99%.

International audience; The Solid Electrolyte Interphase (SEI), formed during the first cycles of life in lithium-ion batteries, contains a variety of lithium salts, with direct effect on the aging performance of the battery. In this work, we investigate the impact of addition of SEI lithium salts (LiF, Li2CO3, LiOH, Li2O, LiOCH3 and LiOC2H5) in the electrolyte on the cycling ability of graphite and LiNi1/3Mn1/3Co1/3O2 (NMC) electrodes. Results show that NMC is more sensitive to salt addition than graphite material. Furthermore, results demonstrate that both LiOH and Li2O have a negative effect on the SEI formation. Conversely, Li2CO3, LiOCH3 and LiOC2H5 are beneficial and promote the formation of a polymeric coating on the SEI. Finally, the impact of the presence of LiF on the SEI depends mainly on its concentration. The effect of the presence of additives capable of complexing lithium salts such as the glyme series, CH3O[CH2CH2O]nCH3 (Gn, with n = 2, 3 or 4), is investigated by cyclic voltammetry, galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). Results show that the glymes chain length is a determining factor in their complexation mechanism, which depends on both the nature and the concentration of the lithium salt.

International audience; The Li7MnN4 structural response upon the first Li extraction insertion cycle is highlighted using in operando XRD experiments. A 3-phases mechanism involving two biphasic regions for 0.1 less than or similar to x less than or similar to 0.8 and 0.8 less than or similar to x less than or similar to 1.2 in Li7-xMnN4 and a solid solution behaviour (1.2 less than or similar to x less than or similar to 1.5) explains its electrochemical fingerprint. These successive structural transitions do not change the cubic symmetry of the cell and induce a limited cell contraction (similar to 7%) associated to a reversible mechanical strain. This finding partly explains the excellent cycle life of this promising negative electrode for Li-ion batteries. (C) 2013 Elsevier B.V. All rights reserved.

The variation in excess thermodynamic properties such as molar volume, viscosity, dielectric constant, Gibbs energy of activation of flow, and surface tension have been determined for {ethylene carbonate (EC)+dimethyl carbonate (DMC)} and {propylene carbonate (PC)+dimethyl carbonate (DMC)}, as a function of mole fraction over the entire composition range, atT=298.15 K or 313.15 K. Polynomial regressions have been fitted with the results. From all these results, qualitative and semi-quantitative information has been obtained about the strength and nature of the interactions between the molecules.

Lithium nickel oxide exhibits a departure from stoichiometry (Li1 − zNi1 + zO2) consisting in the presence of extra-nickel ions within the lithium sites. Using optimized experimental synthesis conditions, compositions very close to the ideal stoichiometry (z = 0.02) can be obtained. By using the sensitivity of the lithium site isotropic temperature factor to the stoichiometry, the amount of extra-nickel ions can be determined in a very precise way. The loss of reversibility at the first cycle is mainly related to the change in the oxidation state of the extra-nickel ions, which induces a local collapse of the structure and makes difficult the lithium re-intercalation. A systematic structural study of LixNiO2 phases has been performed by extended X-ray absorption fine structure (EXAFS) as well as X-ray and electron diffraction. In the case of the starting Li0.98Ni1.02O2 phase, a local distortion of the NiO6 octahedra, resulting from a dynamic Jahn-Teller effect of low spin trivalent nickel ions has been evidenced from the EXAFS study. For the partially de-intercalated materials (0.50 < x < 0.75) which crystallize in the monoclinic system, the EXAFS study shows that the NiO6 octahedra are only slightly distorted due to the occurrence of a hopping phenomenon between NiIV and NiIII. Electron diffraction experiments show the existence of a superstructure due to a peculiar lithium-ion ordering. Systematic electrochemical studies have shown that this ordering is strongly sensititve to the presence of extra-nickel ions.

Electrochemical intercalation of unsolvated lithium into pitch carbon fibres P100 and natural graphite UF4 has been carried out in LiClO4-ethylene carbonate electrolyte. The reversible electrochemical capacity for a current equal to 7 μA/mg is 260 mAh/g for P100 carbon fibres and about 350 mAh/g for UF4 graphite, respectively. During the first discharge (reduction) an electrochemical capacity greater than the theoretical value (372 mAh/g) corresponding to LiC6 is obtained. This excess of capacity can be related to the formation of a passivating layer on the carbon surface. Analysis of this layer by means of transmission electron microscopy (electron diffraction, electron energy loss spectroscopy, and imaging) and Fourier-transform infrared spectroscopy has shown that this layer is composed of lithium carbonate Li2CO3 and alkylcarbonates of lithium ROCO2Li. Formation of Li2CO3 occurs at potentials in the 1−0.8 V range versus Li + Li , and formation of lithium alkylcarbonates then follows at potentials below 0.8 V. We then attributed the voltage plateau at 0.9 V versus Li + Li observed in the electrochemical waves to the reduction of ethylene carbonate into Li2CO3. Transmission electron spectroscopy revealed the presence of lithium chloride in the electrolyte which appears as small rods.

International audience; Thermal evolution of the layered oxide Li2/3Co2/3Mn1/3O2, showing a T#2 stacking and prepared by a Na/Li ion exchange in P2-Na2/3Co2/3Mn1/3O2, was investigated by thermal analyses and X-ray diffraction. A thermal expansion of the T#2 orthorhombic unit cell is observed from 25 to 350 °C; from 350 °C the T#2 stacking is destabilized to the benefit of an O6-type stacking obtained from the former through slab gliding. The T#2 to O6 phase transformation is allowed to occur from a stacking with larger interlayer distances and the lithium ions in tetrahedral sites to a stacking with smaller interlayer distances and the lithium ions in octahedral sites. This phase transition from T#2 to O6 is reversible, even though its kinetic can be very slow: the thermal treatment of the T#2-type Li2/3Co2/3Mn1/3O2 phase at 450 °C with a quenching in air has shown to stabilize the O6HT-Li2/3Co2/3Mn1/3O2 phase. At temperatures higher than 450 °C, the layered oxide Li2/3Co2/3Mn1/3O2 is gradually decomposed into Li2MnO3 and Co3O4. First electrochemical tests performed in lithium batteries have revealed that O6HT-Li2/3Co2/3Mn1/3O2 delivers as positive electrode material a high reversible capacity of 230 mAh*g-1 over two voltage domains around 3 and 4 V vs Li+/Li.

A new vanadium iron oxide has been synthesized starting from V 2 O 5 xerogel through an exchange reaction. In its Rietveld-determined structure, (FeO 6 ) apex sharing octahedra link V 2 O 5 ribbons and increase the three-dimensional character of the material. This latter point seems to improve the electrochemical behaviour when compared with V 2 O 5 . Especially, in terms of cycle life, a capacity of 210 Ah/kg is maintained after 40 cycles in the potential window of 3.8-2 V instead of 150 Ah/kg for V 2 O 5 .

We have studied the effects of several parameters that influence the electrochemical intercalation of lithium ions into various carbonaceous materials: massive samples of pyrographite PGCCL (Le Carbone Lorraine), bulky pitch-based graphitized carbon fibres P100-S (Amoco) and divided natural graphite powder UF4 (Le Carbone Lorraine). The electrochemical Li+ intercalation has been achieved in electrolytic solutions composed of a solvent, ethylene carbonate and a conducting salt, LiClO4. We have shown previously that such an electrolyte allows the intercalation of unsolvated lithium ions up to the richest stage-I LiC6 composition without apparent solvent decomposition. The electrochemical behaviour of the electrodes in such electrolytes was followed either by chronopotentiometry (galvanostatic charge/discharge cycles) or by cyclic voltammetry. The use of micro-computers, able to conduct the experiments by imposition of charge or potential steps followed by cell relaxations, has allowed to obtain data on the kinetics of Li+ intercalation. The electrochemical behaviour of the graphitic electrode is strongly dependent on its morphology. Moreover, the decrease of the size of the crystalline domains during prolongated cyclings has been shown particularly in massive pyrographite samples. Such an electrochemical grinding of the electrode has obviously a positive effect on its performances characterized by a noticeable increase in the maximum x composition reached (x refers to the LixC6 composition). It appears also that the use of poly(vinylidene difluoride) (PVDF) leads to side reactions that have a negative effect on the performances of the electrodes.

The Sn[BPO 4 ] 0.4 composite material is composed of three main constituents: the electrochemically active Sn 0 species, the BPO 4 buffer matrix, and an interfacial amorphous Sn II borophosphate phase which acts as a link between the other two, improving the cohesion of the whole composite. In this paper, we report an investigation of the effect of the reaction time on structure and size of this interfacial layer formed between the Sn 0 and the BPO 4 particles. 119 Sn Mossbauer spectroscopy shows an increase in the amount of the oxidized Sn II species with the increase of the reaction time following a quasi-kinetic profile. Operando Mossbauer spectroscopy allowed the study of the transformation of the interface at the beginning of the first electrochemical cycle, indicating that the big irreversible loss during the first discharge is closely related to the increase of the amount of Sn II in the amorphous interface.

A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB 0.6 P 0.4 O 2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn 0.72 [BPO 4 ] 0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO 4 matrix. The electrochemical responses of ATCO and Sn 0.72 [BPO 4 ] 0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530 mAh g −1 , respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by 119 Sn Mossbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous Sn II composite oxide and shows that in the case of Sn 0.72 [BPO 4 ] 0.28 , the surface of the tin clusters is mainly formed by Sn II in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn 0 . The determination of the recoilless free fractions f (Lamb–Mossbauer factors) leads to the effective fraction of both Sn 0 and Sn II species in such composites. The influence of chemical composition and especially of the surface-to-bulk tin species ratio on the electrochemical behaviour has been analysed for several Sn x [BPO 4 ] 1− x composite materials (0.17 x 0.72 [BPO 4 ] 0.28 as active material exhibits interesting electrochemical performances (reversible capacity of 500 mAh g −1 at C/5 rate).

Cobalt substituted α-nickel hydroxides obtained by precipitation techniques have been used as positive electrodes of NiCd batteries. As these materials are indefinitely stable in KOH solution, the electrochemical cycling between α and γ phases allows up to 1.3 e− per (Ni+Co) atom to be reversibly exchanged at the C/5 rate. Nevertheless, during long-range cycling, a slow evolution from the γ/α couple to the β(III)/β(II) couple occurs. It has been assigned to a partial reduction of Co3+ ions to Co2+ ions at the end of the discharge process. The evolution of the number of exchanged electrons (NEE) versus the cobalt amount is discussed.

α-Turbostratic cobalted nickel hydroxides have been obtained by precipitation, with an NaOH solution, from nickel and cobalt salts. Several preparation methods have been developed in order to obtain a material containing Ni2+ and Co3+ ions. Depending on the experimental procedure, carbonate and sulfate anions are inserted between the (Ni, Co)(OH)2 slabs, in order to compensate for the excess of positive charge due to the presence of trivalent cobalt ions in the hydroxide. These materials have been characterized by chemical analysis, X-ray diffraction, TGA, and u.v.-visible spectroscopy. The resulting αCo3+ phase is stable in KOH medium if the cobalt amount is at least equal to 20%. By contrast, the αCo2+ hydroxide is spontaneously transformed to a β(II) hydroxide, whatever the cobalt amount.

Ab α′-cobalt-substituted nickel hydroxide has been prepared from a β(II)-substituted nickel hydroxide by an oxidation to a γ-type phase followed by a reduction. This α′ Co 3+ -hydroxide crystallizes in the hexagonal system with a P 3-type hydroxyl packing ( a = 3.1 A, c = 23.5 A). β(II)- and α′-cobalted phases have been characterized by chemical analysis, TGA, u.v.-visible and i.r. spectroscopies. In both materials cobalt ions remain in the trivalent state. In α′ Co 3+ -hydroxide, the excess of positive charge is compensated by carbonate anions which are either inserted between the M(OH) 2 slabs, or adsorbed on the particles. The infrared study shows that inserted anions are totally hydrogen bonded with intercalated water molecules ( D 3 h symmetry), while the adsorbed ions are linked to the nickel or cobalt ions in substitution of hydroxyl groups. In β Co 3+ -hydroxide, the charge compensation due to the presence of trivalent cobalt ions is provided by chemisorbed carbonate anions and by a proton deficiency in the sheets. The bonding between the inserted carbonate anions and the Co 3+ cations increases the slab cohesion; as a result the α′ Co 3+ -phase ( x Co ⩾ 0.2) is stable indefinitely in KOH medium.

Reduction of a carbonaceous electrode in LiClO 4 -ethylene carbonate electrolyte results in the development of a surface layer formed of Li 2 CO 3 and different lithium alkylcarbonates identified both by electron energy loss and FT-IR spectroscopies.

International audience; A model was proposed to describe the exchange reaction of sodium by lithium in P2 crystals, it was based first on the formation of nucleation centers and then on the growth of O2 domains in P2 crystals from these nucleation centers...

A model was proposed to describe the exchange reaction of sodium by lithium in P2 crystals. The exchange consists on the formation of nucleation centers and then on the growth of O2 domains in P2 crystals from these nucleation centers. Octahedral environments for lithium ions are obtained when one slab over two glides by (2/3,1/3,0) or by (1/3,2/3,0) in P2 structure. The existence of two different gliding vectors should lead to stacking faulted structures that can be simulated using DIFFaX software. The comparison of simulated and experimental XRD patterns for O2–LiCoO2 (ex-Na0.7CoO2) has shown that in that case the growth of the O2 domains in the P2 crystals is faster than the formation of nucleation centers.