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Cycled electrodes of CoFe2O4 and CuFe2O4 were analyzed by 57Fe Mossbauer spectroscopy. On decreasing the recording temperature, the spectra evidence the superparamagnetic−ferromagnetic transition of metallic iron formed during the reduction of iron oxides in a lithium cell. In addition, the full reoxidation of iron to the 3+ oxidation state is evidenced after cell recharge. As compared with CoFe2O4, the presence of copper led to three effects: a lower percentage of surface atoms, a higher average oxidation state of surface iron atoms, and smaller metallic particles in the reduced state. The relationships between the Mossbauer spectra and particle size and morphology of the raw spinel materials are studied. The charging process involves an important reordering of iron atoms between bulk and surface locations in CoFe2O4, which leads to minor differences in the spectra of the charged electrodes of both compounds.

In recent years, metallic tin and tin compounds have proven to be interesting electrode materials for lithium batteries. However, detailed information about the mechanism of reaction in phosphate compounds is needed to improve the performance of some previously examined and future electrode materials containing these species. In the present work, powerful techniques for the study of the local environments of the atoms, such as 119Sn Mossbauer spectrometry and 7Li and 31P MAS NMR, are used to obtain basic information on the processes involved during the discharge/reduction of the electrode material. The results allow extracting valuable information about the possible interactions between the participating atoms and the surrounding framework.

A high-voltage (5 V) LiCo 0.8 Fe 0.2 MnO 4 electrode with spinel-type structure has been prepared. 57 Fe Mossbauer spectra reveal high-spin Fe 3+ ions in octahedral coordination in the pristine sample, which are oxidized to tetravalent iron ions. Surface treatments with zinc and magnesium have been applied. Zinc and magnesium were homogenously distributed, according to EPMA and mapping analysis, while the spinel structure is maintained. The magnesium and the zinc treatments drive to better electrochemical performance and capacity retention.

Novel compositions Li[LixNi1−x]O2, 0

LiGayCo1−yO2 solid solutions with a layered crystal structure (0 ≤ y < 0.75) were prepared under high-pressure (3 GPa) at 850 °C using a piston–cylinder type apparatus. This is in contrast to the solubility of Ga in the layered LiCoO2 structure at atmospheric pressure, which is strongly limited, and reaches a maximum value of y = 0.1 at 700 °C. The structure of Ga substituted LiCoO2 is characterized by XRD analysis and IR spectroscopy. It has been found that Ga substitutes for Co in the CoO2 layer (3a site), while Li and O are in their normal positions (3b and 6c, respectively). The progressive replacement of Co by Ga leads to a linear increase in the mean M–O bond distance and to a smooth decrease in frequency of the main vibration of the GayCo1−yO2 layer, thus indicating a random Co/Ga distribution. The electrochemical performance of LiGayCo1−yO2 as a cathode material in lithium ion cells has been evaluated in potentiostatic and galvanostatic experiments. The de-intercalation voltage of the LiGayCo1−yO2 solid solutions increases and the reversible capacity decreases with increasing gallium content.

Single-phase oxides with Li[Mn 2− y Co y ]O 4 (0≤ y ≤1) stoichiometry and cubic spinel structure have been prepared by using the lactate precursor method. The oxides were alternatively quenched or slow cooled from 750°C. X-ray diffraction and EPR spectroscopy show that Co and Mn are disordered over 16d spinel sites for samples obtained by air quenching. Local environment of Mn 4+ was assessed by comparison of the observed EPR spectra for Li[Mn 2− y Co y ]O 4 compositions with the EPR signal from Mn 4+ in LiMnCoO 4 and the EPR spectrum of LiMn 2 O 4 . Thus, a local Co/Mn ordering is found for spinels obtained by slow-cooling. The use of these materials as the cathodic active compound in lithium cells reveals a higher capacity but lower capacity retention in the 3–4 V regions for metal-quenched samples as compared with slow-cooled products.

We studied the reduction mechanism of SnO in lithium cells by X-ray absorption near OK and SnL I edge spectroscopy, 119 Sn Mossbauer spectroscopy and X-ray diffraction. The reduction mechanism is complex, involving mixed valence intermediate compounds. In the interval 0≤Li/Sn≤2 the main reaction corresponds to a partial reduction of Sn II , which is partially reversible, regenerating the tin oxide during the charge. For Li/Sn greater than two, LiSn bonds are formed, but SnO interactions are still present. The charge within this interval also partially regenerates tin oxide, but the reversibility does not extend to Li/Sn lower than two. At low voltage and very large depth of discharge, the formation of LiSn alloys and Li 2 O clearly takes place, with negligible SnO interactions.

The chemical environment of Sb atoms in misfit layer sulfides (SbS)pTS2 (T = Nb, Ti and Ta) was examined by using 121Sb Mossbauer spectroscopy (MS) and X-ray photoelectron spectroscopy (XPS). 121Sb Mossbauer spectra exhibited an asymmetric profile that can be interpreted by assuming two different coordination numbers for trivalent Sb ions. However, these data do not give evidence for the presence of a significant Sb atom fraction of valence similar to metallic antimony as reported by X-ray single-crystal structure calculations. Sb 3d peak profiles were found to be highly symmetric and to suggest the presence of a single electronic state for Sb atoms within the SbS lattice. Although the binding energy of Sb 3d electrons in Sb-containing misfit layer sulfides was found to coincide with that in Sb2S3, the Wagner−Auger parameter values are intermediate between those reported for Sb2S3 and metallic Sb.

Ni3+ EPR measurements were used to investigate the electronic structure and ion distribution of Li1−x(NiyCo1−y)1+xO2 (y = 0.13 and 0.8 ≤ y ≤ 1.0) solid solutions prepared between 450 and 800°C. The data on the Ni3+ distribution were obtained from the analysis of the EPR line width. The results show that a transition from non-random to a random Ni Co distribution in the NiyCo1−yO2 slabs occurs between 650 and 750°C. 6Li solid state MAS NMR and magnetic susceptibility measurements are in good correspondence with this interpretation.

Step potential electrochemical spectroscopy data of lithium anode cells using VSe2−ySy(0≤y≤0.5) compounds as cathode material and LiClO4 solutions in PC as electrolyte were studied. On increasing y, a lower extension of the intercalation process was observed, due to the loss of a second insertion step corresponding to lithium ion occupancy of tetrahedral sites. In contrast, the reaction rate increased with sulfur content. VSe2−ySy/LiCoO2 lithium-ion cells were cycled to test the electrochemical behaviour of the vanadium chalcogenides as anodic material. A better capacity retention was observed for y = 0.3. The effect of current density on the performance of the cells was also evaluated.

A new method for the preparation of ultrafine LiCoO2 with a layered crystal structure was developed, which consists in thermal pyrolysis of homogeneous lithium-cobalt-citrate precursors. Atomic scale mixing of Li and Co is achieved by citric acid acting as a chelating agent. Electron spectroscopy of concentrated Li-Co-citrate solutions with Li:Co:Cit=1:1:1 and Li:Co:Cit=1:1:2 reveals that the predominant species at pH=7 are [Co(C6H5O7)]− and [Co(C6H5O7)2]4− complexes. Freeze-drying of the two types of solutions leads to the formation of LiCo(C6H5O7).nH2O and (NH4)3LiCo(C6H5O7)2.nH2O precursors, where Co2+ ions are complexed by one and two triionized citrate ions, respectively, and Li+ ions serve as counter ions. Between 400–600 °C, the thermal decomposition of these metal-citrate precursors yields LiCoO2 with layered and pseudo-spinel structure, the proportion between them being depending on: (i) the Co/citrate ratio; (ii) the concentration of the freeze-dried solution; (iii) the heating rate. At 400 °C, the most defectless layered LiCoO2, consisting of hexagonal individual particles with dimensions of 120–170 nm, is a product of the bis-citrate decomposition with a slow heating rate. For this sample, heating up to 600 °C does not affect the crystal size dimensions. For ultrafine layered LiCoO2 and LiCoO2 obtained by solid state reaction at high-temperatures (850 °C), the deintercalation and intercalation reactions proceed in the 3.95 – 3.99 and 3.86 – 3.88 voltage intervals, respectively. For defect trigonal LiCoO2, additional oxidation and reduction peaks at 3.7 – 3.8 and 3.4 – 3.5 V were observed. We did not succeed in preparing monophase LiCoO2 with pseudo-spinel structure.

The misfit layer sulfide of composition (PbS)1.18(TiS2)2has been studied as a host material for the intercalation of sodium. The discharge curve profile using propylene carbonate (PC) as the solvent of electrolyte showed that the intercalation process is complex with the appearance of an extended plateau which suggests the formation of a multiphase region. In fact, an intermediate phase of sodium content 0.2 mol per formula unit, with basal spacing of 29.9 A, which exceeds by 12.4 A the repeating unit PbS–TiS2–TiS2, has been observed. This result is interpreted on the basis of solvent cointercalation. PC molecules are located at the interlayer region defined at the interface TiS2–TiS2. The increase in the sodium content promotes the release of PC molecules out of the layers. The interlayer expansion of the new phase formed is similar to that observed upon intercalation with sodium naftalide and is consistent with the location of sodium ions in the interstitial sites defined by two consecutive sulfur slabs. Under room conditions this phase absorbs water. The final expansion of ca. 6 A is consistent with a bilayer hydration process.

Acid treatment at 0°C of Li 1-x (Ni y Co 1-y ) 1+x O 2 solid solutions yields delithiated well crystalline oxides Li 0.5 (Ni y Co 1-y ) 1+x O 2 which do not contain protons. For the nearly stoichiometric nickel-rich oxides, removal of more than 20% of the lithium leads to a monoclinic distortion of the rhombohedral unit cell. Electron paramagnetic resonance (EPR) of low-spin Ni 3+ ions shows that for up to 0.2 extracted lithium, the generated Ni 4+ ions are statistically distributed in the NiO 2 layers while above 0.2 extracted lithium the Ni 4+ ions trend to order. During acid delithiation the oxidation of Ni 3+ to Ni 4+ ions proceeds prior to the oxidation of Co 3+ to Co 4+ as for a nonaqueous electrolyte. Discharge-charge cycles of lithium cells using acid-delithiated oxides as cathode materials show a significant improvement of reversibility compared with the charge-discharge cycles of the corresponding pristine samples

Monophase Li1-x(NiyCo1-y)1+xO2 oxides (0 ≤ y ≤ 0.4 and 0.8 ≤ y ≤ 0.9) with a layered structure (R3m space group) have been prepared by interaction of (NiyCo1-y)3O4 (0 ≤ y ≤ 0.4) and NiyCo1-yO (0.8 ≤ y ≤ 0.9) with LiOH at low temperature (450°c). As in the case of high-temperature analogues, cobalt substitution for nickel stabilizes the Ni3+ ions and improves the two-dimensionality of the crystal lattice. Acid treatment of LT and HT oxides leads to a partial dissolution of the solid and to removal of lithium and "impurity" cobalt and/or nickel from LiO2 layers of the trigonal framework. For cobalt-rich oxides, the ion extraction is accompanied by partial Li+/H+ exchange, especially for LT samples. Acid-delithiated oxides are studied as cathode materials in lithium batteries. The resulting cells show a high value of the initial voltage (4 V), which allows a direct discharge of the cell without previous charge. For LT samples, the discharge and charge processes occur at lower voltage (especially for Co-rich oxides) and the reversibility of the cell is lower as compared to that of HT analogues. The better reversibility of the cell in the 4.0-3.2 V range is found for HT Ni-rich oxide. The composition of the acid-treated oxides can be recovered without an enhancement polarization of the cell. XRD analysis and IR spectroscopy show good reversibility of lithium insertion and extraction reactions by chemical and electrochemical procedures.

Since the launch in 1990 of the first commercial lithium-ion batteries based on LiCoO2 cathode materials, a considerable progress has been accomplished in the field of the solid state chemistry and electrochemistry of lithium-manganese spinels, which are thought to be alternative cathode materials. In order to improve the cycling stability of lithiummanganese spinels, the partial replacement of Jahn-Teller Mn3+ ions by transition metal ions or electrochemically inactive metal ions has been successfully applied.

First studies of the ternary system SnSe-Bi(2)Se(3) developed in 1960s and 1970s have revealed the existence of a nonstoichiometric trigonal phase with a wide range of compositions. In this study, an almost stoichiometric phase, corresponding to the composition SnBi(4)Se(7), has been identified and isolated. The structure has been determined by X-ray diffraction and the local environment of Sn atoms analyzed by Mössbauer spectroscopy. This phase has a rhombohedral structure, space group Rthremacr;m, with hexagonal lattice parameters a = 4.1602(5) Å and c = 38.934(3) Å. The unit cell contains three slabs, each one composed of seven atomic layers according to the sequence Se-Bi-Se-(Bi,Sn)-Se-Bi-Se. Bismuth atoms partially occupy two sites, 3a (0, 0, 0) and 6c (0, 0, z) with z = 0.4285, while tin atoms partially occupy only one site, 3a. Selenium atoms are placed in two different 6c sites, with z(1) = 0.1350 and z(2) = 0.7108.

cited By 10; International audience; 119Sn Moessbauer spectroscopy, X-ray diffraction and electrochemical experiments were carried out to characterize the reaction mechanism of lithium with spinel phases of the Cu2S-In2S3-SnS2 system. This analysis reveals an irreversible part of the mechanism linked to the reduction of the cations involving a spinel to rocksalt transformation followed by a structural breakdown, and a reversible part linked to the formation of lithium-metal alloys. The electrochemical investigation has shown interesting reversible capacities for these materials, and their possible use as anode materials in lithium-ion cells.

New mixed spinel oxides with LiNi y Co 1-2y Mn 1+y O 4 (y = 0.2, 0.3, and 0.4) stoichiometries have been synthesized under different annealing temperatures and tested as cathode materials in lithium batteries. High-purity cubic spinel-phase products were obtained between 700 and 950°C, in which the lattice parameter increases with nickel content. The structural and textural properties of the powder samples were studied by X-ray diffraction (XRD) and scanning electron microscopy and correlated with the electrochemical behavior. From these experiments, the best performance was obtained for LiNi 0.4 Co 0.2 Mn 1 404 cathodes with 1-5 μm regular octahedral particles, which developed capacity values close to 120 mAh/g with a good capacity retention. The ex situ XRD patterns of the partially charged electrodes were characteristic of a single cubic phase in which lattice parameter decrease with lithium extraction for all compositions.

Etude de la pyrolyse sous vide. Cinetique du 1er ordre: vitesse de decomposition proportionnelle a la quantite de reactif non decompose

The thermal evolktion of chemically lithiated Co3O4, γ-Fe2O3 and α-Fe2O3 has been stkdied by DTA and Tk technikkes. The prodkct of lithiation of Co3O4 contains LixCo3O4, knreacted Co3O4 and traces of LiOH and Li2CO3. LixCo3O4 decomposes exothermally into Co3O4 and Li2O at ca . 150–300°C. At 400–500°C, the reaction betkeen Co3O4, lithikm oxide and carbonate takes place leadink to a mixtkre of LiCoO2 and knreacted Co3O4. Lithiated γ-Fe2O3 contains LixFe2O3, knreacted γ-Fe2O3 and traces of LiOH and Li2CO3. This mixtkre transforms exothermally into a LiFe5O8 strkctkre at ca . 250–350°C. At 400°C a nek phase of rock-salt strkctkre occkrs (a = 4.029 A), that remains knaltered belok 750°C. The thermal behaviokr of lithiated α-Fe2O3 is apparently different to that foknd in lithiated γ-Fe2O3. α-LiFeO2 and α-LiFe5O8 kere the phases present above 550°C.

The electrochemical behaviour of new doped Li-M-Mn-O (M = Al, Fe, Ni) spinel oxides in liquid electrolyte lithium cells was studied. The insertion electrode materials were obtained by heating stoichiometric amounts of thoroughly mixed LiOH and M x Mn1− x CO3 (M = Fe, Ni; x = 0.08−0.15) or Al x Mn1− x (CO3) (OH) y , in the case of Al, at 380 °C in air for 20 h. The transition metal-doped samples, particularly those containing Ni or obtained at low temperatures, where the resulting spinel was cation-deficient and highly disordered, exhibited the best cycling performance in the potential window 3.3−2.3 V. Cell capacity was retained by 80% after 200 cycles. Capacity fading was observed on increasing the firing temperature, together with improved crystallinity and the disappearance of cation vacancies. This impaired electrochemical behaviour is ascribed to a Jahn-Teller effect, which induces an X-ray-detectable cubic-tetragonal phase transition upon lithium insertion. The phase transition was undetectable in the low-temperature samples. The influence of the Jahn-Teller distortion is thus seemingly lessened by a highly disordered structure.

Solid solutions in the α-LiGaO2–LiNiO2 system were prepared over the whole concentration range under high pressure (3 GPa) at 700 °C in oxygen-rich atmosphere. The structure of LiGayNi1−yO2 solid solutions was characterized by XRD analysis, EPR and IR spectroscopy. It was found that Ga substitutes for Ni in the NiO2 layer (3a site), while Li and O are in their normal positions (3b and 6c, respectively). The occupancy of Ni in the Li site is negligible for Ga-substituted oxides. The progressive replacement of Ni by Ga leads to an unusual concentration variation of the a-parameter: at 10% Ga additives, there is a contraction of the a-parameter together with the expansion of the c-parameter. The concentration variation of the a-parameter can be related to increased trigonal distortion of GayNi1−yO2 layers upon Ga substitution. The electrochemical performance of LiGay(Ni1−xCox)1−yO2 solid solutions as a cathode material in lithium ion cells has been evaluated in potentiostatic experiments. During the first charge, there is an irreversible peak at about 4.7 V, which was compared with the electrochemical Li extraction from layered oxides characterized with a partial mixing of lithium and metal ions in the metal layers. After the first charge, a reversible electrochemical intercalation of Li is achieved. The effect of Ga on the potential of lithium extraction/insertion in LiGay(Ni1−xCox)1−yO2 was discussed.