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Li 3 FeN 2 displays rich and complex structural response upon electrochemical oxidation/reduction. During the first lithium deintercalation, 4 voltage plateaus corresponding to a total charge transfer of 1.14 e − per iron cation take place. Combining operando Mossbauer spectroscopy and X-ray diffraction, we evidence 3 biphasic reactions involving four orthorhombic phases. Despite a derived anti-fluorine type structure, Li 3 FeN 2 oxidation induces a unidirectional contraction along b axis. Mossbauer spectroscopy established a partial iron oxidation (∼90%). Therefore the participation of the nitrogen network as additional redox center is suggested to explain the observed extra capacity. Moreover, an unexpected low spin to high spin crossover took place for ∼10% of Fe 3+ during the oxidation of Li 3 FeN 2 . Based on the cationic mixing recently demonstrated and the anisotropic structural response, two possible explanations are discussed; (i) a significant deformation of 8 g lithium sites, which contain ∼10% of iron cations or (ii) migration of these cations into the neighboring octahedron 8 j . This High Spin Fe +3 contribution remains almost constant until the end of the oxidation.

The kinetics of the electrochemical lithium insertion reaction in the as-prepared Li7MnN4 has been investigated using ac impedance spectroscopy as a function of cycles and temperature. The results are compared and discussed with that obtained for an optimized Li7MnN4 sample obtained by ball-milling. From this comparison, a promoting effect of a lower crystallite size on the electrochemical kinetics is evidenced. For the first time an experimental evaluation of the activation energy for Li diffusion in the as-prepared and the ball-milled Li7MnN4 is obtained. The lower activation energy obtained for the ball-milled nitride, Ea = 0.28 eV against Ea = 0.42 eV for the pristine material is responsible of the better rate capability and significant improvement of the electrochemical behaviour especially in terms of cycling properties: at high rate of 5C, a remarkable and stable capacity of 120 mAh g−1 is obtained over 50 cycles which competes very well with the LTO anode material.

An optimization of the specific capacity exhibited by the best layered lithiated cobalt nitride Li 2.20 Co 0.40 N is proposed by using a conditioning electrochemical oxidation up to 1.1 V before cycling in the 1.1 V–0.02 V potential range. This initial charge process allows the Co 3+ /Co 2+ redox couple to be involved in the cycling process in addition to the Co 2+ /Co + couple as in the 1 V–0.02 V voltage range. A new electrochemical fingerprint is obtained with a single step at 0.4/0.8 V for the discharge-charge process and a specific capacity of 300 mAh g −1 at C/5 which constitutes a huge improvement compared to 130 mAh g −1 recovered in the conventional 1 V–0.02 V potential window. This high capacity value and the excellent capacity retention of 100% over at least 75 cycles make Li 2.20 Co 0.40 N a promising anode material for Li-ion batteries.

The chemical reactivity in air of the promising metallic nitride Li7MnN4 as negative electrode for Li-ion batteries has been studied. The evolution of the ageing process with exposure time has been examined by XRD and the degradation kinetics has been determined. This cubic metallic nitride is found to be much less sensitive to the air atmosphere than that exhibited by the lamellar nitridocobaltates Li3−2xCoxN (0.1 ⩽ x ⩽ 0.44). A fast oxidation step in air leads to the delithiated Li6.2MnN4 phase after a few hours and is thereafter progressively destroyed by reaction with moisture leading to the formation of LiOH⋅H2O and Li2CO3. Electrochemical experiments on various aged samples support these results. The demonstration of Li7MnN4 storage in dry air is showed to constitute a relevant solution to preserve the integrity of the nitride host lattice and then its excellent electrochemical properties.

The high rate performance of ball-milled Li 7 MnN 4 as negative electrode material in lithium-ion batteries has been investigated at C and 5 C rates. An optimization of ball-milling experimental conditions allows to synthesize this metallic nitride with attractive and improved specific capacity and cycle life compared to the pristine compound. The outstanding finding is its excellent cycle life over 50 cycles with a capacity of 240 mAh g −1 at 1 C rate in the potential range 1.6 V/1 V. Even at 5 C the promoting effect of ball-milling results in a remarkable high and stable capacity of 120 mAh g −1 upon cycling, which compares very well with the behavior achieved for Li 4 Ti 5 O 12 while the pristine material is practically inactive.

International audience; Monodisperse and small tin nanoparticles were prepared from a 2,2'-bipyridine-tin(+2) chloride complex using sodium borohydride as reducing agent. When the synthesis was conducted in the presence of graphite, Sn particles with an average diameter of ca. 29 nm well-dispersed at the surface of graphite were obtained. Electrochemical lithium insertion was carried out in these materials. A stable reversible capacity of ca. 480 mA h g(-1), value 37% higher than that of pure graphite, was found.

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.

We report a systematic study of the layered lithium nitridocuprates Li3 − xCuxN with 0.1 ≤ x ≤ 0.39. The structural data obtained from experimental XRD patterns, Rietveld refinements and unit cell parameters calculation vs x, indicate that copper (I) substitute interlayer lithium ions in the parent nitride Li3N to form the Li3 − xCuxN compound without any Li vacancy in the Li2N− layer. Electrochemical results report Li insertion into the corresponding layered structures cannot take place in the 1.2/0.02 V voltage range as in the case of lithium into nitridonickelates and nitridocobaltates. However, in the initial charge process of Li3 − xCuxN at 1.4 V leading to a specific capacity higher than 1000 mA h/g, the oxidation of copper and nitride ions is probably involved inducing a strong structural disordering process. As a consequence a new rechargeable electrochemical system characterized by discharge–charge potential of ≈ 0.3 V/1.2 V appears from the second cycle. Cycling experiments 0.02 V voltage/0.02 V range induce a complete destruction of the layered host lattice and the presence of Cu3N in the charge state suggests a conversion reaction. The capacity recovered in the 1.4/0.02 V range practically stabilizes around 500 mA h/g after 20 cycles.

Graphite/SnSb composites were prepared by solution-phase reduction of SnCl 2 and SbCl 5 in the presence of graphite powder using either t -BuONa-activated NaH or t -BuOLi-activated LiH. Crude and washed materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission gun-scanning electron microscopy (FEG-SEM). Electrochemical lithium insertion was carried out in both types of composites using voltammetry or galvanostatic charge/discharge techniques. It appeared that graphite-SnSb composites prepared using t -BuOLi-activated LiH as reductant displayed the highest reversible capacity (ca. 500 mA h g −1 ). This phenomenon is likely in relation with a better dispersion and grafting of metal particles on graphite, as suggested by FEG-SEM and TEM analyses. However, such dispersion appeared to increase significantly the irreversible capacity.

An EC/DEC [40:60% (v/v)] solvent mixture has been added in various amounts to the ionic liquid (IL) hexyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N1116-NTf2) in the presence of LiNTf2 (lithium bis(trifluoromethylsulfonyl)imide) as lithium salt for possible use as electrolytes in lithium-ion batteries. These electrolytes exhibit a larger thermal stability than the reference electrolyte EC/DEC [40:60] + LiNTf2 1 M when the percentage of the IL exceeds 30% (v/v). All studied electrolytes are glass forming ones with an ideal glass transition temperature of ca. −85 °C(±5 °C), which has been determined by application of the VTF theory to conductivity and viscosity measurements and confirmed by DSC (Tg = −90 ± 5 °C). An electrochemical window of about 5 V versus Li/Li+ was measured at a glassy carbon electrode. The cycling ability of the optimized electrolyte N1116-NTf2/EC:DEC (40/60% (v/v)) + 1 M LiNTf2 has been investigated at a titanate oxide (Li4Ti5O12) and a cobalt oxide (LixCoO2) electrodes. Cycling the positive and the negative electrodes was conducted successfully with a high capacity and without any significant fading.

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.

We report the first example of an intercalation compound based on the nitrogen framework in which lithium can be intercalated and deintercalated. A comparison of the structural and electrochemical properties of the ternary lithium cobalt, nickel and copper nitrides is performed. Vacancy layered structures of ternary lithium nitridocobaltates Li3−2xCoxN and nitridonickelates Li3−2xNixN with 0.10 ⩽ x ⩽ 0.44 and 0.20 ⩽ x ⩽ 0.60, respectively, are proved to reversibly intercalate Li ions in the 1 V–0.02 V potential range. These host lattices can accommodate up to 0.35 Li ion par mole of nitride. Results herein obtained support Li insertion in vacancies located in Li2N− layers while interlayer divalent cobalt and nickel cations are reduced to monovalent species. No structural strain is induced by the insertion–extraction electrochemical reaction which explains the high stability of the capacity in both cases. For the Li1.86Ni0.57N compound, a stable faradaic yield of 0.30 F/mol, i.e. 130 mAh/g, is maintained at least for 100 cycles. Conversely, the ternary copper nitrides corresponding to the chemical composition Li3−xCuxN with 0.10 ⩽ x ⩽ 0.40 do not allow the insertion reaction to take place due to the presence of monovalent copper combined with the lack of vacancies to accommodate Li ions. In the latter case, the discharge of the lithium copper nitrides is not reversible. Keywords: Nickel nitrides, Lithium insertion, Negative electrode, Lithium batteries

Electrochemical lithium insertion was carried out in tin–graphite composites obtained by two different preparation processes. In the first graphite was mixed with the products obtained by reduction of SnCl 4 with Na tert -Butanoate ( t -BuONa)-activated NaH (two-step synthesis). The second used materials synthesized by reducing SnCl 4 with a graphite and ( t -BuONa)-activated NaH suspension in THF (one-pot synthesis). Both composites were characterized by X-ray diffraction and transmission electron microscopy . It appeared that the tin particle size was controlled by the reduction time of SnCl 4 . The stability of the electrochemical capacity of composites prepared by the two-step synthesis is dependent on the tin particle size: a stable capacity upon cycling was shown with subnanometer particles while a capacity fade was observed with larger nanoparticles. In materials prepared by the one pot synthesis, tin was present either as nanopartcles supported on graphite or as free aggregates. An initial reversible capacity of 630 mA hg −1 decayed to a constant value of 415 mA hg −1 after 12 charge/discharge cycles. It was hypothesized that the fraction of tin bound to graphite contributed to the stable reversible capacity while free tin aggregates were responsible for its decay.

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.

SnCl 2 was reduced in the presence of graphite by t -BuONa-activated NaH. The resulting (tin/graphite)-based system was composed of nanosized tin particles deposited on the graphite surface and of free tin aggregates. Lithium electrochemical insertion occurs in graphite and in tin. A reversible specific charge of 500 mAh/g is found stable upon cycling. This value is lower than the maximum theoretical one (650 mAh/g) assuming a Sn/12C molar composition and the formation of the highest lithium content alloy Li 22 Sn 5 . It is suggested that the part of tin responsible for the stable reversible capacity is the one bound to graphite. To the contrary, free tin aggregates could contribute to a capacity which decreases upon cycling in connection with the volume changes accompanying lithium insertion/extraction in/out of these aggregates.

For the purpose of obtaining an improved performance of the graphite negative electrode of Li-ion batteries, a novel graphite–tin composite has been synthesized by reduction of tin chloride (SnCl 2 ) with KC 8 in THF medium. This composite contains nano-sized tin particles dispersed on the graphite surface and free tin aggregates. Lithium electrochemical insertion occurs both in graphite and in tin. An experimental reversible specific charge of 489 mA h g −1 is found stable upon cycling. Such a value is lower than the maximum theoretical one of 609 mA h g −1 suggesting that only a part of tin is involved in the lithium insertion/extraction process. This part of active tin responsible for the stable capacity could be that bound to graphite. To the contrary, free tin aggregates could contribute to an extra capacity that decreases upon cycling in relation with the volume changes that occurs during alloying/dealloying.

Group 15 element–graphite M/C composites were prepared by reduction of MClx chlorides (AsCl3, SbCl5, BiCl3) by KC8 in THF. Arsenic and antimony were both amorphous: antimony appeared as a film-like material, formed of aggregated nano-sized particles covering parts of the graphite surface; arsenic was present as large graphite supported particles. On the contrary, bismuth was present as crystalline metal nanoparticles distributed on the graphite surface. Amorphous As and Sb–graphite composites displayed stable reversible capacities of 310 and 420 mA h/g, respectively while that of crystalline Bi–graphite materials decreased regularly upon cycling. Although these practical capacities were lower than the expected theoretical ones corresponding to the formation of Li3M compounds, it appeared that, in the presence of graphite, amorphous solids exhibiting a (partly) covalent character like As and Sb gave better long life cycling properties than the crystalline and metallic bismuth. It was very likely that our one step synthesis could generate bonds between graphite and (partly) covalent solids reducing consequently the volume expansion effects occurring during cycling. On the contrary, metallic solids like bismuth that were not inclined to bond with graphite behave, upon cycling, as corresponding massive metals.

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.

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.

Metal-based composites are under investigation as possible negative-electrode materials in lithium-ion batteries. In this paper, we present a new composite material constituted of antimony particles dispersed on graphite. The antimony–graphite compound is prepared by antimony pentachloride reduction with KC8 in tetrahydrofuran. The high reversible capacity of 420 mAh g−1 and the good stability suggest that the association of antimony with graphite allows not only to improve reversible capacity but also to prevent the metal from particle pulverisation generally occurring during lithium alloying.

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.

Antimony-based graphite composite has been studied as a potential material for negative electrodes for lithium-ion batteries. This material has been synthesised by antimony pentachloride intercalated graphite compound reduction using an original method consisting in the use of activated sodium hydride as reducing agent in tetrahydrofuran. The composites have been characterised by X-ray diffraction and transmission electron microscopy. Graphite deintercalated and antimony nanoparticles embedded in organic matrix have been observed. The electrochemical properties of this new material as lithium-ion anode have been investigated. The obtained results highlight not only the leading role of the particle size of the active material but also the influence of a stabilising organic matrix. In our case, volume changes generally occurring during insertion/extraction of lithium into/from metallic host material, which lead to rapid disintegration and deterioration of Li-alloy electrode seem to be avoided. Indeed the presence of the matrix and the conductivity of graphite work in unison to prevent antimony nanoparticles against agglomeration and lead to a good cycling stability of such composite systems.

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 new ac impedance spectroscopy method is proposed to follow the charge–discharge processes of nickel oxo-hydroxide electrode (NOHE) in KOH media and thereafter to determine their state of charge (SOC), involving in situ measurements of the impedance between two electronic contacts soldered on opposite edges of the electrode. A transmission line (TL) model is developed and fitted to experimental results. The physical significance of its parameters is discussed, taking into account one- and two-phase domains.

As a part of a study on the optimisation of the electrolyte for high-density energy lithium batteries, transport properties of concentrated LiClO4 solutions in γ-butyrolactone (BL) have been investigated. The effect of the salt concentration (C) on the viscosity (η) of BL solutions has been discussed in term of the Jones–Dole equation. At concentrations higher than 0.2 M, the molar conductivity (Λ) of LiClO4 solutions follow a C1/3 cube root law which is predicted by the quasi lattice model first introduced by Gosh. In this model, the ions of the strong binary electrolyte are distributed in a lattice-like arrangement (fcc). The experimental value found for the slope of Λ vs. C1/3 relation is in fair agreement with the calculated one. The effect of the temperature on the viscosity and the conductivity of electrolyte solutions have been examined. These two transport processes are well described by Arrhenius type laws from which the activation energies for the viscosity Eaη and conductivity EaΛ are deduced. The variations of Eaη and EaΛ with salt concentration are respectively dependent on C and C4/3 as predicted by the quasi lattice model.

The electrochemical characteristics of Li1−xNi1+xO2 samples have been extensively investigated as a function of the lithium deficiency x in the narrow composition range 0.008–0.065. In particular, the electrochemical and structural behaviours of the quasi-stoichiometric compound (x=0.008) have been proved to be strongly different from those exhibited by a sample with x=0.025. The faster kinetics for Li transport combined with structural changes which are minimized in the quasi-ideal compound explain the lack of notable polarization voltage and the good cycle life of the latter cathode material with a stable capacity of 140 A h/kg over 40 cycles at C/10 rate. In addition, interesting and useful correlations (i) between the cathode impedance and the lithium deficiency and (ii) between the evolution of the cathode impedance and the cycling performance have been established.

Lithium cannot be electrointercalated into graphite in an electrolyte containing propylene carbonate (PC) as the only solvent species. In order to improve the cycleability of graphite electrodes in the presence of PC two methods were used: use of solvent mixtures containing PC and halogen-substituted solvent molecules (α-bromo-γ-butyrolactone and methyl chloroformate); impregnation of the graphite electrode by halogenated solvents prior to cycling in PC-based electrolytes. It appears that the reversible capacity is increased by ∼10% when such halogenated solvent molecules are used. Moreover, the cycleability is dependent on the nature of lithium salt, the concentration of halogen solvent and the specific current.

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.

New lithium rich graphite intercalation compounds have been synthesized. They display a van der Waals space containing five alternating intercalated layers, three of lithium and two of oxygen corresponding to an interplanar distance d I equal to 665 pm. The compound ideally formulated as Li 2 C 6 O 0.5 has been obtained from the second-stage NaC 6 O 0.5 either by its electrochemical reduction in LiClO 4 -ethylene carbonate electrolyte or by its direct reduction with molten lithium. This yellow material, of biintercalation type, is characterized by a repeat distance along c-axis, I c , equal to 1035 pm. This value corresponds to the addition of an interplanar spacing of 370 pm resulting in lithium intercalation in the van der Waals gap of NaC 6 O 0.5 and of another one of 665 pm, resulting in the exchange of sodium by lithium in the five intercalated layers of the starting material. Another compound, formulated as LiC 6 O 0.5 , is a classical stage 3 material in which the intercalated part is the five alternating lithium–oxygen layers also present in Li 2 C 6 O 0.5 . Its repeat distance along c-axis is equal to 1340 pm. All these Li x C 6 O 0.5 compounds contain sodium clusters trapped in their bulk. Lithium species appear to be organized to form a hexal structure as in LiC 6 while there is no occurrence for a structural organization of oxygen present as peroxide ions.

A new yellow lithium-rich graphite intercalation compound formulated Li2C6O0.5 has been synthesized in ambient conditions by electrochemical intercalation of lithium into the blue stage two NaC6O0.5 compound in LiClO4–ethylene carbonate electrolyte. This new compound is a quasi stage 1 compound of biintercalation type characterized by an identity period along c-axis (Ic) equal to 1035 pm. Such a value is the sum of an interplanar distance of 370 pm resulting in lithium intercalation in the Van der Waals gap of NaC6O0.5 and of another one of 665 pm related both to the intercalation of lithium and to the concomitant exchange of sodium by lithium in the five intercalated layers of the pristine stage two compound. Preliminary studies of the structural 2D-organization give evidence for lithium species arranged in a classical hexal structure as in LiC6 or LiC12 compounds. Sodium resulting from sodium ion reduction appears in the form of clusters distributed in the new material.

The electrochemical intercalation of lithium into graphite was studied in various electrolytes containing chloroethylene carbonate (ClEC), ethylene carbonate (EC) and propylene carbonate and their mixtures as solvents and LiClO4, LiBF4 and LiAsF6 as lithium salts. The reduction of ClEC and EC, catalyzed on the surface of the graphite electrode, starts at potentials equal to 1.7 and 0.9 V, respectively, and leads to the formation of reduction products which passivate the carbon surface. The effect of the nature of the lithium salts on the properties of the interfacial layer is also examined. With LiBF4, the first reduction of the carbon electrode results in a massive reduction of the electrolyte, especially LiBF4, that limits the reversible lithium intercalation. With the electrolytes containing ClEC, the reversible intercalation is observed with formation of LiC6. Moreover, a slight excess of capacity compared with LiC6 is observed after the first cycle. It could be attributed to an extra fixation of lithium in the interphase layer generated by C–Li(ads.)–Cl bonds.

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%.

Partial molar volumes at infinite dilution VMX∞ of three electrolytes (LiClO4, LiCF3SO3 and LiPF6) have been determined by vibrating-tube densimetry in pure propylene carbonate (PC), ethylene carbonate (EC) and dimethylcarbonate (DMC) and, for LiClO4, in some mixtures of EC with DMC and PC. Vmx∞ are strongly dependent of the nature of the pure or mixed solvents. Absolute ionic molar volumes of the Li ion and associated anions have been deduced from the partial molar volume of tetra-alkylammonium salts in the same solvents. For this purpose the concept of van der Waals volume and packing density proposed by King has been employed. In all solvents under investigation, the volume of the Li ion has similar values: VLi+∞ ≈ 5 cm3/mol. This result is different from what is obtained using the tetraphenylarsonium tetraphenylborate assumption. The differences among polyatomic anions volumes are greater than expected and strongly dependent on the solvents' nature. These effects are discussed in terms of ion-solvent interactions: ion solvation, packing effect in the solvation shell and electrostriction. Implication of these findings for Li batteries is briefly discussed.

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.

Reversible electrochemical intercalation of unsolvated lithium into graphite previously treated either in LiClO4-ethylene carbonate (EC) or in LiClO4-dimethyl carbonate (DMC) solutions was carried out in a LiClO4-propylene carbonate (PC) electrolyte. Under these conditions, graphite exfoliation did not occur, allowing the graphite anode to cycle reversibly. The modifications of the structure and the morphology of the graphite during its reduction in PC-LiClO4 electrolyte was studied by transmission electron microscopy (electron diffraction, imaging) and X-ray diffraction studies.

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.

A crystal chemistry study of LiNi1 − yCoyO2 phases, used as positive electrode in lithium batteries, is presented. These materials crystallize in the rhombohedral system (space group: R3m) with a layered structure. Rietveld profile refinement of the X-ray data shows that for low substitution amounts (≤ 0.20) extra-nickel ions are always present leading to the Li1 − zNi1 + z − tCotO2 (t = y(1 + z)) formula (z ∗ > 0), while for y ≥ 0.30, a pure 2D structure is obtained (z = 0). The stabilization of the 2D character of the structure by cobalt substitution in lithium nickelate leads to the improvement of the electrochemical properties.

Electrochemical intercalation of unsolvated lithium into pyrographite has been carried out in LiClO4-ethylene carbonate electrolyte. Pure phases have been isolated and characterized by X-ray diffraction studies. The orientated texture of pyrographite has allowed the study of the different families of Bragg reflections (001, hk0, hkl) especially for stage I LiC6, 3D stage II LiC12 and dilute stage II ‘LiC18’ compounds. Experimental data and some theoretical models have been compared.

Nickel hydroxide electrodes have been studied by ac impedance spectroscopy at rest potential and during charge or discharge. A transmission line model is proposed based on behaviour similarities with electrochemical intercalation into graphite. Considering here that protons and electrons react inside the solid, partial electronic and protonic conductivities of the two β-type phases Ni(OH) 2 and NiOOH in equilibrium are taken into account. Even if 1-D and so basically limited to a homogeneous deposit of constant thickness, this model approximates reasonably experimental observations.

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 structural features of the potassium vanadium pentoxide bronze K 0.25 V 2 O 5 , as well as the main characteristics of its sol-gel synthesis are reported. The electrochemical properties of this bronze are discussed in terms of crystallographic data and compared to that obtained with the same bronze prepared through solid state reaction.