The search for new materials that could improve the energy density of Li-ion batteries is one of today's most challenging issues. Many families of transition metal oxides as well as transition metal polyanionic frameworks have been proposed during the past twenty years. Among them, manganese oxides, such as the LiMn2O4 spinel or the overlithiated oxide Li[Li1/3Mn2/3]O2, have been intensively studied owing to the low toxicity of manganese-based materials and the high redox potential of the Mn(3+)/Mn(4+) couple. In this work, we report on a new electrochemically active compound with the 'Li4Mn2O5' composition, prepared by direct mechanochemical synthesis at room temperature. This rock-salt-type nanostructured material shows a discharge capacity of 355 mAh g(-1), which is the highest yet reported among the known lithium manganese oxide electrode materials. According to the magnetic measurements, this exceptional capacity results from the electrochemical activity of the Mn(3+)/Mn(4+) and O(2-)/O(-) redox couples, and, importantly, of the Mn(4+)/Mn(5+) couple also.

We demonstrate low-potential intercalation of lithium in a solid-state metal phosphide. A topotactic first-order transition between different but related crystal structures at room temperature takes place by an electrochemical redox process: MnP4 <--> Li7MnP4. The P-P bonds in the MnP4 structure are cleaved at the time of Li insertion (reduction) to produce crystalline Li7MnP4 and are reformed after reoxidation to MnP4, thereby acting as an electron storage reservoir. This is an unusual example of facile covalent bond breaking within the crystalline solid state that can be reversed by the input of electrochemical energy.

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Crystal structure and oxygen stoichiometry in LiMn 1.5 Ni 0.5 O 4−␦ , a potential lithium-battery cathode, vary with temperature, as observed in samples quenched from different temperatures and by in situ diffraction and thermogravimetry techniques. When prepared in high O 2 pressure, this cation-ordered spinel is oxygen-stoichiometric, ␦ = 0, space group P4 3 32. Upon heating between 650 and 680°C, increasing oxygen deficiency occurs exclusively in MnO 6 octahedra and Mn-O-Mn bonds, which induces a volume increase of the 12d octahedra, a reduction of Mn as shown by X-ray absorption near-edge structure, equalization of Mn-O and Ni-O bond lengths, and disordering of Mn, Ni on octahedral sites. Hence, the transformation to space group Fd3 ¯m, shown by Rietveld refinement of variable-temperature neutron diffraction data, is a direct consequence of oxygen loss from the structure. On further oxygen loss, a second phase transformation occurs to give a cation-deficient cubic rock salt phase, ␦ ϳ 0.65, at 950°C, which loses more oxygen at higher temperatures until, at 1100°C, the material is essentially a stoichiometric, single-phase cation-disordered rock salt, space group Fm3 ¯m. A second spinel phase persists in small amounts from 950 to 1100°C. Differences in electrochemical behavior depend on sample preparation and correlate with the oxygen content of LiMn 1.5 Ni 0.5 O 4−␦ when used as a cathode in Li test cells.

Although cobalt hydroxide is currently added to Ni(OH ) 2 paste to prepare nickel composite electrodes used in Nibased rechargeable alkaline batteries, its redox chemistry in alkaline media is still poorly documented. The Co(OH ) 2 ACoOOH oxidation reaction in KOH media was investigated, and found to be dependent upon the experimental conditions, namely, temperature, oxidizing agent and reaction time. In addition, this reaction was shown, as determined by means of X-ray diffraction, electronic microscopy and atomic absorption measurements, to occur through a two step mechanism process involving first a dissolution process followed by a solid state reaction. This dissolution step enables preparation, by adjusting the cycling conditions, of cobalt oxyhydroxide with well defined morphology and texture, thereby providing an opportunity to optimize its efficiency as an additive in nickel electrodes.understand how CoOOH forms in electrochemical cells. In