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Lithium-rich spinel Li1.2Mn1.8O4 thin film electrodes operated at 3 V/Li+/Li are studied by means of X-ray photoelectron spectroscopy (XPS), mainly on the basis of the evolution of the Mn2p XPS peak during the electrode cycling. The analysis of this core peak has long been debated in literature given its complex character. Based on manganese oxide references, MnO (Mn2+), Mn2O3(Mn3+) and Li2MnO3(Mn4+), we propose a deconvolution method to identify each Mn oxidation state. This method is then used for the deconvolution of Mn2p XPS peaks of bulk lithium-rich spinels Li1+xMn2-xO4 (0 ≤ x ≤ 0.25) for validation before proceeding to the study of cycled Li1.2Mn1.8O4 thin film electrodes. Electrochemical measurements exhibit significant capacity loss during the first cycle. Based on XPS analyses, this phenomenon could be explained by mechanical breakup of parts of the electrode. A stable behavior during subsequent cycles is then observed. The presence of Mn2+ species (XPS) at the most top surface of the electrode and the significant polarization observed during the discharge illustrate the kinetical limitation of the two-phase reaction, despite the reduced thickness of the electrode material.

Constant miniaturization of electronic devices opens the way to the development of thin film microbatteries (TFB). For this type of devices, the use of an all-solid-state thin film technology has many advantages over conventional lithium cells. These microbatteries are thin, bendable and can be produced with a customizable shape for integration in microelectronic devices. Moreover, without liquid electrolyte, they are safer. With the aim to support the industrial production of these TFBs, adequate tools for understanding the electrochemical behavior of the complete microbattery and the identification of their possible failures that can occur have to be developed. In this context, the Electrochemical Impedance Spectroscopy seems to be a good compromise for cells characterization. Widely used for the characterization of liquid electrolyte-based batteries, this technique has been less applied to all solid state batteries, mainly because of the difficulty to work with a two-electrode system. There has been no comprehensive study deeply explaining the impedance evolution during the entire life of a microbattery. In this paper, physical characterizations of individual active materials and aging experiments have been performed in order to undoubtedly assign each EIS contributions, and to propose a more comprehensive electrical model for this family of commercial all-solid-state microbatteries.

Thin film positive electrodes of lithium-rich manganese oxide spinels were prepared by radiofrequency magnetron sputtering from a LiMn 2 O 4 ceramic target at a total pressure close to 2 Pa. Post-annealing treatments were necessary to get well-crystallized thin films displaying interesting electrochemical performances. Raman spectrum exhibiting several well-defined bands between 296 and 635 cm −1 is typical for the lithium-rich spinel. Based on ICP, RBS and XRD analyses, the thin films composition is close to Li 1.2 Mn 1.8 O 4 . The latter is also in accordance with a Mn 3+ /Mn 4+ ratio close to 0.1 deduced from XPS measurements. Best electrochemical performance (capacity value, cycling life) between 2 V and 3.5 V vs Li + /Li was obtained for thin films annealed at 600 °C. A volumetric capacity of 52 μAh cm −2 μm −1 (close to about 90% of the theoretical value) was obtained at the first cycle at a C/100 regime. Contrary to most studies carried out on spinel thin films cycled in the 3 V range, no appreciable degradation of the discharge capacity was observed after few tens of cycles at room temperature, highlighting the beneficial effect of substituting 20% of Mn ions by Li ions and the presence of microvoids in thin films that limits the effect of strain generated from volume variation during the Li insertion/deinsertion process.

LiCoO2 thin films were synthesized via an easy one-step electrochemical-hydrothermal route using ethanol–water blends as solvent. The influence of the synthesis parameters - i.e. ethanol/water ratio, temperature, pressure, reaction time and current density - on the formation of layered R3¯m phase and on its electrochemical behavior in lithium cells was investigated. X-ray diffraction (XRD) shows the formation of well-crystallized R3¯m LiCoO2 thin films with preferred (1 0 1) orientation, without any trace of spinel-like (LT-LiCoO2) phase or cobalt oxide Co3O4 impurities. LiCoO2 films with controlled orientation exhibit a specific capacity close to the theoretical value, and excellent capacity retention even at high current density. Experimental results reveal that electrodeposition under hydrothermal conditions allows high deposition rates reaching 500 nm min−1.

All-solid-state thin film batteries based on sputtered pyrite electrodes, a lithium phosphorus oxynitride electrolyte and a lithium anode were prepared and characterized. The successive reduction of both S22− and Fe2+ species led to an impressive volumetric discharge capacity, five times higher than the one for LiCoO2. Excellent reversibility and capacity retention were obtained during the first and the subsequent 800 charge–discharge cycles. A continuous cycling in the low voltage domain was found to be detrimental to the reversibility of the conversion reaction, suggesting a progressive evolution of the phase distribution inside the electrode. The initial capacity was easily recovered after few full oxidation cycles. Keywords: Pyrite, Thin film, Conversion reaction, Lithium microbattery, Solid-state battery

International audience; The current sustained demand for "smart" and connected devices has created a need for more miniaturized power sources, hence for microbatteries. Lithium-ion or "lithium-free" all-solid-state thin-film batteries are adapted solutions to this issue. The capability to carry out spatially resolved chemical analysis is fundamental for the understanding of the operation in an all-solid-state microbattery. Classically cumbersome and not straightforward techniques as TEM/STEM/EELS and FIB preparation methods could be used to address this issue. The challenge in this work is to make the characterization of Li-based material possible by coupling ion-milling cross section preparation method and AES techniques to characterize the behavior of a LiCoO2 positive electrode in an all solid state microbattery. The surface chemistry of LiCoO2 has been studied before and after LiPON deposition. Modifications of the chemical environments characteristic of the positive electrode have been reported at different steps of the electrochemical process. An original qualitative and a semiquantitative analysis has been used in this work with the peak deconvolution method based on real, certified reference spectra to better understand the lithiation/delithiation process. This original coupling has demonstrated that a full study of the pristine, cycled, and post mortem positive electrode in a microbattery is also possible. The ion-milling preparation method allows access to a large area, and the resolution of Auger analysis is highly resolved in energy to separate the lithium and the cobalt signals in an accurate way.

International audience; Iron molybdate thin films are studied here as a possible electrode material for future Li and Na microbatteries working in a lower potential range than currently used systems. Monoclinic Fe2(MoO4)3 thin films are successfully deposited using radio frequency (RF) sputtering and an annealing treatment. The electrochemical behaviour of the obtained electrodes against Li and Na is then studied in a coin cell configuration with liquid electrolytes. The redox processes ruling the insertion/deinsertion of Li+ and Na+ are investigated by means of XPS (X-ray Photoelectron Spectroscopy). The results highlight a different behaviour depending on the alkali, with a better redox reversibility for sodium at the end of the first charge. For subsequent cycles however, improved capacity retention is evidenced for cycling versus lithium as compared to sodium which was attributed to the properties of the SEI layer.

International audience; Silicon which has a theoretical capacity around 3500 mAh g−1 and low insertion/deinsertion potentials is one of the most promising candidates to replace graphite as a negative electrode in lithium-ion batteries. Electrochemical performances of Si electrodes are highly dependent on the quality of the SEI. Therefore, the effect of an electrolyte additive, the vinylene carbonate (VC) on electrochemical performances was investigated on sputtered silicon thin films which constitute a simple system (avoiding the use of binders or any conducting additive material). The addition of only 2% of VC significantly improves the capacity retention as well as the coulombic efficiency leading to a capacity retention of 84% after 500 cycles and a coulombic efficiency around 99.5%. To explain the behaviour differences, thorough electrochemical analyses (capacity, coulombic efficiency, polarization at half charge...) combined with scanning electron and atomic force microscopies were carried out. Some correlations have been established between the electrochemical performances and the morphology evolution of the electrode. Thus, VC limits the formation of cracks induced by repeated expansion/contraction cycles and the liquid electrolyte/electrode interactions. In addition, the mechanical pressure locally applied to the thin film allows to maintain a dense morphology and hence has a beneficial effect, too. These two key parameters limit the deterioration of the electrode over cycles.

International audience; All-solid-state Li/LiPONB/TiOS microbatteries were manufactured at the pilot scale on silicon substrate. In a first attempt, the characterization of the active materials constituting the microbattery was achieved in order to determine their accurate composition, structure and morphology. Finally, a thorough electrochemical characterization was carried out on all-solid-state cells. Excellent performances were noted in terms of cycle life (with more than 1000 cycles), efficiency and self-discharge (less than 5% per year). In addition, the positive electrode highlighted a high volumetric capacity close to 90 μAh cm−2 μm−1 when cycled at 100 μA cm−2 between 1 V and 3 V vs. Li+/Li.

International audience; C–LiFePO4 composites were synthesized by mechano-chemical activation using iron and lithium phosphates, and also cellulose as carbon precursor; this mixture was treated with 2 thermal treatments (“slow” or “fast” treatment) and 2 temperatures (575 °C or 800 °C). The four synthesized samples were pure olivine-type materials (XRD), but chemical analyses and Mössbauer spectroscopy show Li/Fe and P/Fe ratios larger than 1 and the presence of 5–6 at.% of Fe3+. Three hypotheses were considered to explain the presence of Fe3+ ions: (i) a chemical formula Li1 + xFe1 − xPO4 for the olivine-type phase, (ii) a mixture of olivine-type LiFePO4 and Fe3+ containing impuritie(s) or (iii) LiFePO4 with Fe3+ surface defects. These hypotheses were checked using different characterization methods such as X-ray diffraction, neutron diffraction and magnetic measurements, hypothesis (i) was shown not to be valid but none of hypotheses (ii) and (iii) was definitely confirmed. One can assume either the presence of a Fe3+-rich phase (amorphous or nanocrystalline) or the occurrence of surface defects which can play a significant role as far as nanomaterials are concerned.

Single-phase compounds Li2Mn3MO8 (M = Mg, Co, Ni, Cu) have been synthesized and investigated as replacements of LiMn2O4 for lithium intercalation below 3 V. They all retain the spinel structure, with cation ordering on the octahedral M (16d) site for M = Mg only. Cell parameters vary as Co < Ni < Mg ≈ Cu < Mn and average M–O bond lengths as Co ≈ Ni < Cu < Mg < Mn. Lithium was intercalated both chemically and electrochemically. Electrochemical potential step spectroscopy shows features typical of a two-phase intercalation reaction, in spite of a manganese valence range mostly above the accepted Jahn–Teller distortion limit (50% Mn3+). The tetragonal distortion is only noticeable at high intercalation levels. It yields c/a distortion values much lower for M = Co or Ni than for unsubstituted LiMn2O4. However, no improvement in electrochemical cyclability was obtained. Magnetic susceptibility measurements show features typical of frustrated systems, as expected for the 16d sublattice, and confirm that chemical intercalation reaches lithium contents close to the theoretical limit (one additional Li per AB2O4 formula unit). For cobalt substitution, bond length and Curie constant analysis both lead to a charge distribution Li2[(Mn4+)2Mn3+Co3+]O8 rather than Li2[(Mn4+)3Co2+]O8.

The structural features accompanying the lithium extraction/insertion process in a fluorine-substituted spinel oxide with formula LiMn2(O3.74F0.26) were studiedin situusing Bellcore-type plastic batteries directly placed in a synchrotron X-ray beam. The initial material contains two phases, a cubic spinel and a slightly orthorhombically distorted one (major phase). It becomes entirely cubic on extraction of 0.17 Li atoms per formula unit. The lithium extraction reaction around 4 V vs Li/Li+can be divided into three regions as a function of lithium contentx: (1) a single-phase range for 0.59≤x≤0.83, (2) a two-phase range for 0.23≤x≤0.59 with equilibrium potential 4.122 V, (3) a narrow single-phase range III for 0.18≤x≤0.23. These three domains are fully reversible. With the exception of the presence of the initial orthorhombic distortion, the main features of the so-called electrochemical 4 V plateau are very similar to those of stoichiometric LixMn2O4.

Neutron powder diffraction has been carried out on two series of Li–Mn–O samples with spinel structure, which have been shown to lose oxygen with respect to initial stoichiometric spinels: (i) Li1.05Mn2O4quenched from 800 or 925°C, (ii) “Li1.33Mn1.67O4” (nominal) treated with ammonia gas at 200°C. The structural refinements unambiguously show that both 925°C quenching and low-temperature ammonia treatment induce oxygen vacancies in the spinel lattice. However, the mechanism of oxygen loss is markedly different between quenchings at 800 and 925°C. While the latter actually corresponds to the introduction of anionic vacancies at constant cation composition, the former is due to a rearrangement of the Li/Mn ratio in the spinel phase and the formation of an additional lithium-rich phase Li2MnO3. The presence of vacancies induce a significant increase in atomic displacement parameters of oxygen.

Lithium phyllomanganate, Li x MnO 2 · yH 2 O (x = 0.25–0.29, y ≈ 0.6) with the birnessite structure cannot be obtained directly by oxidation of Mn(OH) 2 in Li-containing medium. It was obtained by a two-step topotactic reaction involving an acidic treatment of sodium phyllomanganate, followed by ion exchange in LiOH at room temperature. The lamellar lithium manganate is characterized by electron diffraction, magnetic measurements and thermogravimetry, showing that the structure is retained after water loss up to 500 °C. The material cannot be chemically oxidized by bromine, cerium(IV), or nitryl fluoborate. However, sodium and lithium phyllomanganates can be delithiated reversibly in electrochemical cells at ca. 4 V vs. Li Li + .

LiAlMnO4 and LiMg0.5Mn1.5O4 have been investigated as replacements of LiMn2O4 for lithium intercalation below 3 V. The decomposition of acetate and carbonate precursors was studied by thermogravimetry. Solid state reactions yielded ‘LiAlMnO4’ with manganese valence < 4 and always containing impurity phases such as LiAl5O8 or LiMn2O4. The intercalation behaviour was studied potentiostatically in lithium cells using both liquid and solid electrolytes, and by X-ray diffraction on intercalated cathodes. The structural and electrochemical behaviour of ‘LiAlMnO4’ is very similar to that of LiMn2O4, and gives lower capacities on cycling. Lithium intercalation in LiMg0.5Mn1.5O4 includes three reduction steps between 2.8 and 1.6 V, corresponding to the intercalation of ca. 0.58, 0.22 and 0.25 Li atoms, respectively. The total initial capacity is 180 mAh/g, but also drops on cycling, mainly due to the collapse of the second step corresponding to the critical threshold around Mn+3.5, where the tetragonal distortion due to the Jahn—Teller effect takes place.

Topotactic reactions in Li– M –O systems with M = Mn, Ti, V, Fe are described in the framework of composition–valence diagrams, using the Li/ M and the transition metal valence ν( M ) as coordinates. We show that this representation is very convenient to depict and compare the various parameters associated with insertion/extraction reactions, i.e., the evolution of ν( M ), the extent of intercalation x in Li x M O y , the electrochemical potentials, and the cell parameter changes. New directions are suggested for topotactic reaction in oxides, especially in titanium ones. The composition–valence diagram helped in the detection of inconsistencies in the intercalation potentials in LiFe 5 O 8 , which are corrected using new voltammetric data. We conclude that lithium intercalation in octahedral sites of iron spinel oxides occurs at constant voltage around 1.6 V, whichever the Li–Fe–O host may be.

The behaviour of acidified aged molybdate solutions has been studied. These solutions, which can be reduced to blue molybdenum deposits close to −200 mV(SSE) for 1

LiCoO 2 powders synthesized by a sol/gel process followed by an annealing heat treatment in the range 400–900 °C are systematically characterized using SEM, X-ray diffraction, FTIR and Raman spectroscopy. The composition of the final powder is found to be controlled by the heat treatment temperature. A thorough multipeak fitting analysis of Raman spectra gives access for the first time to the quantitative estimation of the R-3m and Fd3m relative amounts in the LiCoO 2 powders as a function of the post-annealing temperature. The gradual LT–HT phase transformation can therefore be observed: a pure Fd3m phase is obtained at 400 °C, and then the two LiCoO 2 forms coexist from 500 °C to below 700 °C, the R-3m relative amount increasing from 20% at 500 °C to 90% at 600 °C, to be 100% at 700 °C. Cyclic voltammetric measurements confirmed this evolution, showing the typical behaviour of the high performance R-3m layered phase from 600 °C. These results put forward an original and appropriate use of Raman spectroscopy in the field of electrode materials for lithium batteries.

International audience; The effect of vinylenecarbonate (VC) as electrolyteadditive on the properties of the silicon electrode / liquid electrolyteinterface was studied in this paper. Galvanostatic cycling, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the SEI layer properties and the morphology at different stages of the cycling of thin film electrodes. The electrochemical performances were drastically improved by the introduction of a few per cent of VC additive. It was found that the SEI layer formed in VC-containing electrolyte has a different chemical composition and better resists to the stress caused by large volume variations associated with lithiation and delithiation reactions. The chemical and topographic modifications of the electrode surface at various stages of cycling are discussed in correlation with the evolution of the reversible capacity over cycling with and without VC. This study highlights the importance of the SEI which governs the electrochemical performances of Si thin film model electrodes.

International audience; A mathematical model of a Li/LiPON (Lithium Phosphorus Oxynitride)/LiCoO2 all-solid-state thin-film microbattery was developed. It is isothermal, one-dimensional and takes into account lithium diffusion and electron migration in the positive electrode, migration of lithium ions in the solid electrolyte, and charge-transfer kinetics at the electrode/electrolyte interfaces. Model input parameters are determined for the case of a reference microbattery available on the market using a variety of electrochemical techniques such as galvanostatic intermittent titration technique and electrochemical impedance spectroscopy. A good agreement is found between simulation and charge/discharge experimental data, both in galvanostatic and potentiostatic operation, which therefore validates the model. Finally, the temperature dependence of input parameters is introduced into the model, which allows for predicting microbattery operation at different temperatures.

In this study, we report the synthesis of lamellar R-3m LiCoO 2 thin films electrodes for lithium rechargeable batteries by a single step method based on an electrochemical–hydrothermal synthesis in a concentrated LiOH solution with a cobalt salt. This process combines the effect of temperature (between 150 °C and 200 °C), pressure and galvanostatic current. The obtained films were not annealed after the electrochemical–hydrothermal synthesis. For the first time, the theoretical study of the potential–pH diagram of cobalt was carried out at high temperature and high concentration. These calculations show that a pH value higher than 12 is necessary to avoid the direct precipitation of cobalt hydroxide Co(OH) 2 inside the solution. An improvement of the soluble species stability with an increase of the temperature and a decrease of the cobalt concentration is predicted. The influence of the deposition conditions (temperature and concentration) at a constant current density was experimentally studied. X-ray diffraction (XRD) shows the formation of well-crystallized LiCoO 2 thin films. Raman spectroscopy confirmed the achievement of the electrochemically active R-3m LiCoO 2 phase without any trace of the Fd3m phase at temperatures as low as 150 °C. Electrochemical measurements demonstrate good performances of the material synthesized between 150 °C and 200 °C with better capacity retention at higher temperature.

International audience; LiCoO2 thin films were synthesized by sol/gel process using acrylic acid (AA) as chelating agent. The gel formulation was optimized by varying solvent (ethylene glycol or water) and precursors molar ratios (Li, Co, AA) in order to obtain a dense film for positive electrode of lithium batteries. The gel was deposited by spin-coating technique on an Au/TiO2/SiN/SiO2/Si substrate. Thin films were deposited by either single or multistep process to enhance the density of the thin film and then calcined during 5 h at 800 °C to obtain the R-3m phase (HT-LiCoO2). A chemical characterization of the solution was realized by Fourier Transform Infrared (FTIR) spectroscopy. Thermal decomposition of precursors and gel was studied by Thermo Gravimetric Analyses (TGA). Further investigations were done to characterize rheologic behaviour of the gel and solvents affinity with the substrate. Crystallinity and morphology were analyzed respectively by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The formation of R-3m phase was confirmed by the electrochemical behaviour of the gel derived LiCoO2. Cyclic voltammograms and galvanostatic cycling show typical curve shape of the HT-LiCoO2.

International audience; The olivine-like material LiFePO4 was prepared via a continuous hydrothermal synthesis process working from subcritical to supercritical water conditions. The influence of some processing parameters–temperature and reaction time–was investigated in terms of material purity, grain size and morphology. Supercritical conditions were found to be attractive to synthesize in one step a well-crystallized material without impurities. The primary particles size was in the nanometric range. They showed a natural tendency to form micron size agglomerates, which were supposed to be the cause of the limited capacity, as demonstrated through a cross study using laser particle size distribution analysis, electrochemical measurements and XRD at different Li contents.

International audience; A hydrothermal synthesis process working in supercritical conditions (T > 374 °C, P > 22 MPa) and in a continuous mode has been developed for inorganic nanopowder synthesis. This paper presents a review of the past 5 years of research conducted on this process. Numerous materials (oxides: ZrO2, TiO2, Fe2O3..., ferrites: Fe2CoO4..., or BaZrO3) were obtained with specific features. Some technical issues have been solved, that are presented here. Heat transfer was studied, leading to a more efficient design of the reactor. Future developments have been examined through process engineering, in which our group is engaged, especially through CFD modelling.

International audience; A series of carbon-coated olivine phase (C-LiFePO4) was synthesized under argon by mechano-chemical activation, with two thermal-treatments ("slow" or "fast") and two temperatures (575 °C or 800 °C). In spite of similar chemical and structural properties, they showed rather good, but very different, electrochemical behaviors in long range cycling or high rate conditions. All the studied C-LiFePO4 materials were characterized by an inhomogeneous agglomerates size distribution with small primary particles around 100 nm in diameter and by specific surface areas around 20 m2/g. The electronic properties were shown to be highly dependant on the synthesis conditions: as expected the higher the thermal-treatment temperature and the longer the thermal treatment were, the better the degradation of the carboneous precursor and thus the higher the electronic conductivity of the C-LiFePO4 material. This study suggests that good electrochemical performances at high rate and during a long range cycling at constant rate imply, for a given composite, a good coating with high electronic conductivity and small primary particles (here around 100 nm in diameter). The material obtained at 800 °C with the short thermal-treatment synthesis (15 min) satisfies these requirements.

International audience; Because of its surface sensitivity, X-ray photoelectron spectroscopy allowed us to access the mechanisms at the very surface of 100 nm diameter carbon-coated LiFePO4 nanoparticles. A continuous evolution of the Fe3+/Fe2+ ratio was observed at the surface of the particles upon charge and discharge, in good agreement with the change in the average lithium content of LixFePO4 electrode material. These results support these models considering migration of a reaction front along the a-axis inside the cristallites vs. the shrinking-core model, to describe lithium (de)intercalation in LiFePO4. XPS analyses showed also that electrode/electrolyte interface phenomena are minimized using carbon-coated LiFePO4 particles as positive electrode material vs LiCoO2 for instance, despite the nanometric size of the particles.

International audience; Lithium iron phosphate is one of the most promising positive-electrode materials for the next generation of lithium-ion batteries that will be used in electric and plug-in hybrid vehicles. Lithium deintercalation (intercalation) proceeds through a two-phase reaction between compositions very close to LiFePO4 and FePO4. As both endmember phases are very poor ionic and electronic conductors, it is difficult to understand the intercalation mechanism at the microscopic scale. Here, we report a characterization of electrochemically deintercalated nanomaterials by X-ray diffraction and electron microscopy that shows the coexistence of fully intercalated and fully deintercalated individual particles. This result indicates that the growth reaction is considerably faster than its nucleation. The reaction mechanism is described by a 'domino-cascade model' and is explained by the existence of structural constraints occurring just at the reaction interface: the minimization of the elastic energy enhances the deintercalation (intercalation) process that occurs as a wave moving through the entire crystal. This model opens new perspectives in the search for new electrode materials even with poor ionic and electronic conductivities.

The stability of LiFePO4 in water was investigated. Changes upon exposure to water can have several important implications for storage conditions of LiFePO4, aqueous processing of LiFePO4-based composite electrodes, and eventually for utilisation in aqueous lithium batteries. A Li3PO4 layer of a few nanometers thick was characterised at the LiFePO4 grains surface after immersion in water, accompanied by an increase of FeIII percentage in the grains. For first charge–discharge cycles in a lithium battery, no effect was observed on electrochemical performances for a sample of LiFePO4 immersed for 24 h at a concentration of 50 g L−1 without any pH modification. To limit the aging of LiFePO4 during aqueous electrode processing, it is advised to reduce the immersion duration, to concentrate the LiFePO4 suspensions, and not to modify the pH. In addition, since immersion in water mimics an accelerated exposure to air humidity, LiFePO4 should be stored in a dry atmosphere.

In this paper, we report some practical data concerning the electrochemical behaviour of composite lithium iron phosphates, at higher rates of charge–discharge, at lower operating temperatures and during long cycle life tests. These results were collected on composite LiFePO 4 powders (whose submicrometer particles were coated by carbon or boron-based wraps), all obtained from optimized syntheses using mechanochemical activation of an iron (II) precursor as main starting material.

Spinel phases Li-Mn-C with Li/Mn ratios between 0.35 and 0.8 were synthesized. The relationships between composition, manganese valence, vacancy fraction and electrochemical capacity are described using a new composition-valence phase diagram. Electrochemical performances in lithium batteries are compared. The best materials showed constant capacit> 140 Ah/kg in the range 3.5/2 V in liquid electrolyte batteries up to 20 cycles, without the usual capacity drop observed in stoichiometric LiMn204.

even manganese dioxide (MD) forms including natural ramsdellite, β-MnO2 and samples with structures intermediate between these two types, have been analyzed interms of chemical and structural disorder. XRD and IR spectra show that natural ramsdellite contains groutellite, MnO1.5(OH)0.5. The OH absorption band in the 3400cm-1 region is sharp for groutellite, less intense on CMD spectrum, andsuperimposed to a broad and diffuse absorption ranging from 3600 to 2000cm-1 in most γ-MnO2's. The OH groups are associated with Mn+3 defects, while the broad and diffuse absorption band can be assigned to protons in empty MnO6 octahedra, and so related to instable manganese oxydation state between Mn3+ and Mn4+.A potentiostatic study in IM and 7M KOH shows that the stoichiometric oxides, ramsdelliteand β-MnO2, are not reduced, while CMD and EMD are reversibly reduced by H+/-einsertion. In 7M KOH, a reversible reduction occurs for both CMDs and EMDs until -0.2 V, while a heterogeneous mechanism destroys the structure at lower potential (70% capacity loss after 3 redox cycles). Only ramsdellite and β-MnO2 can be cycled reversibly below -0.37 V, but the drained capacity is very low for β-MnO2.The presence of Mn3+ and Mn4+ vacancies associated to structural disorderin synthetic MDs increases their reduction potential and completely modifies the chemicalproperties. This mixed valence state seems to be at the origin of the reduction properties by proton insertion in protonic electrolytes.

Raman and Fourier transform infrared (FTIR) spectroscopy investigations were performed on carbon-coated LiFePO 4 materials differing by the temperature of their thermal treatments (575 and 800°C) and by their electrochemical performance, with that obtained at a higher temperature showing larger reversible capacity and better capacity retention at high rates. Raman spectra gave information on the carbon located at the surface of the LiFePO 4 particles, which was shown for the two samples to be highly disordered with small in-plane correlation lengths (

Structural and electrochemical properties of a new highly rechargeable lithium iron phosphate are described here, Its behavior as cathodic material was also tested in a complete power system based on a nanocrystalline Li 4 Ti 5 O 12 anode and a nonaqueous liquid electrolyte (1 mol L -1 LiPF 6 in ethylene carbonate/dimethyl carbonate). This cell operates with a very flat voltage profile at around 2 V, with very little capacity fading upon cycling, even at a very high rate (4C or 8C). These features, combined with the low cost and the lack of toxicity of the components, make this system an attractive and inexpensive power source for the low voltage electronic market.

LiFePO4 powders were synthesized under two different conditions ~hydrothermal or mechanochemical activation! using iron~II! phosphate and lithium phosphate as starting materials. The samples were characterized by X-ray diffraction, chemical titration, and their electrochemical performance was investigated in terms of cycling behavior and impedance response. We also report the benefit of introducing an electronic conductor precursor ~typically a sucrose! during or after the synthesis to overcome the poor charge transfer associated to the lithium iron phosphate.

In the first part of this paper, we report the discovery of a new lithium manganese oxide, with formulaLi0.25MnO2, formed by the complete transformation of β-MnO2 in the presence of lithium hydroxide or carbonate at 150 °C. The cell parameters of the new phase are: a = 9.36, b = 5.65, c = 4.90 A, β = 102.21 °. The b parameter is twice 2.825 A, a distance typical of cells with structures containing octahedral Mn, such as the initial rutile-type β-MnO2. This compound, however, is not stable upon lithium intercalation under our experimental conditions. The second part of this paper is devoted to an in situ study of the electrochemical lithium intercalation by using an X-ray diffractometer. The study of two different Li1 + αMn2 − αO4 oxides with Li/Mn ratios of 0.50 and 0.69 shows that the tetragonal phase appears immediately from the beginning of intercalation. The reaction is strictly two-phase, even in the case of Li/Mn > 0.50, where the initial Mn oxidation state is well above the theoretical limit for tetragonal distortion (Jahn-Teller effect) of 3.5. The lithiated phases, however, are markedly different with c/a distortions of 1.16 and 1.10 for hosts with Li/Mn ratios of 0.50 and 0.69, respectively.

The cycling of sodium and lithium phyllomanganates in liquid lithium batteries was investigated both by galvanostatical and potentiostatical methods. Slow-scanning voltammograms show the occurrence of a single-phase reaction extending from 3.1 to 2.6 V on discharge for both compounds. On cycling, the voltammogram of Li phyllomanganate smears out, while the current peak narrows in the case of Na. In both cases, the initial capacity of ∼240 Ah/kg drops continuously on cycling between 2 and 4 V. X-ray diffraction shows an important disordering with cycling, with the possible emergence of a cubic-packed, spinel-like structure.

Spinel oxides with compositions LiMn 2 O 4 and Li 1.23 Mn 1.77 O 4 were studied using an air-tight electrochemical lithium cell mounted on an X-ray powder diffractometer. The combination of electrochemical and X-ray data unambiguously shows the appearance of a tetragonal phase as soon as lithium intercalation in the host oxide begins. The lithium intercalation reaction is found to be two-phase for both oxide hosts, in spite of the high initial manganese oxidation state in Li 1.23 Mn 1.77 O 4 (+3.82), which lies well above the expected Jahn–Teller distortion limit (+3.5). The tetragonal distortion is much stronger in lithiated Li 2 Mn 2 O 4 than in Li 1.23+ x Mn 1.77 O 4 .

Li(Ni,M)O2 (M= Al, Co/Al and Mn) materials used as positive electrode materials for Li-ion batteries have been synthetized by a coprecipitation method and then characterized by X-ray and neutron diffraction, magnetic measurements and galvanostatic tests. The thermal degradation mechanism of the Lix(Ni,M)O2 (M = Al, Co/Al et Mn, x = 0.50 et 0.30) deintercalated phases was studied by Thermal Gravimetric Analyses coupled with Mass Spectrometry. Correlation with in situ X-ray diffraction experiments was then achieved to determine the degradation mechanism and to explain the differences in thermal stability observed depending on the material composition. For all studied materials, the degradation occurs in two steps, corresponding to the transition between the initial α-NaFeO2 type phase and a “LiM2O4” pseudo-spinel phase, which evolves into a NiO type phase at higher temperature. Influence of the substituent nature was discussed.; Des matériaux d'électrode positive pour batteries Li-ion de formule Li(Ni,M)O2 (M = Al, Co/Al et Mn) ont été synthétisés par coprécipitation, puis caractérisés par diffraction des rayons X et des neutrons, par des mesures magnétiques et des tests galvanostatiques. La dégradation thermique des phases désintercalées Lix(Ni,M)O2 (M = Al, Co/Al et Mn, x = 0.50 et 0.30) a ensuite été étudiée par analyses thermogravimétriques couplées à la spectrométrie de masse, corrélées à des expériences de diffraction des rayons X in situ, afin d'en déterminer le mécanisme et d'expliquer les différences de stabilité observées suivant la composition des matériaux. Pour tous les composés étudiés, la dégradation se déroule en deux étapes, correspondant à la transition de la phase lamellaire initiale de type α-NaFeO2 en une phase “ LiM2O4 ” de type pseudo-spinelle qui se transforme ensuite, à plus haute température, en une phase dérivant de NiO. L'influence de la nature de l'élément substituant a été discutée.