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Abstract: Structural evolution during topotactical electrochemical lithium insertion and deinsertion reactions in ramsdellite-like Li x Ti2O4 has been followed by means of in situ X-ray diffraction techniques. The starting Li x Ti2O4 (x =1) exists as a single phase with variable composition which extends in the range 0.50≤ x ≤1.33. However, beyond the lower and upper compositional limits, two other single phases, with ramsdellite-like structure, are detected. The composition of these single phases are: TiO2 upon lithium deinsertion and Li2Ti2O4 upon lithium insertion. Both TiO2 and Li2Ti2O4 are characterized by narrow compositional ranges. The close structural relationship between pristine LiTi2O4 and the inserted and deinserted compounds together with the relative small volume change over the whole insertion–deinsertion range (not more than 1.1% upon reduction) is a guaranty for the high capacity retention after long cycling in lithium batteries. The small changes in cell parameters well reflect the remarkable flexibility of the ramsdellite framework against lithiation and delithiation reactions. [Copyright &y& Elsevier]

Abstract: The layered nitrides LiWN2 and Li0.84W1.16N2 are investigated related to their electrochemical performances as possible electrodes for rechargeable lithium batteries. In the case of LiWN2, for which Li and W atoms are ideally ordered in alternating Li and W layers, de-intercalation of lithium proceeds up to 50%. The de-intercalated lithium can be intercalated again subsequently. The reversible reaction is the origin of the high cyclability observed in the corresponding lithium cells. On the other hand, in Li0.84W1.16N2 the Li layers are statistically occupied by tungsten (16%) and lithium (84%). A clear effect of the disordered cationic occupation on the electrochemical behaviour has been found, since for Li0.84W1.16N2 a very low extraction rate is obtained during the first oxidation (0.03 Li per formula unit). In addition, cyclability is rather poor. The very different electrochemical behaviour is explained by the structural differences between both layered nitrides. [Copyright &y& Elsevier]

Abstract: New olivines LiMAsO4 (M=Mn, Fe, Co, and Ni) have been tested as positive electrode in lithium cells. Under the used experimental conditions we did not succeed to remove lithium ions from LiFeAsO4, LiMnAsO4 or LiNiAsO4. More work is needed in order to verify whether the lack of electrochemical activity is intrinsic to these materials, or it is due to kinetical limitations such as particle size and poor conductivity. On the contrary lithium ions could be reversibly deinserted/inserted from/into LiCoAsO4 at average voltages of 4.8 and 4.6V respectively; the delithiated compound maintaining the olivine structural framework. The high pressure polymorph of LiMAsO4 (M=Fe, Co, Ni) crystallizing with the spinel structure did not show any electrochemical activity potentially useful in rechargeable lithium batteries. [Copyright &y& Elsevier]

Abstract: Electron energy loss spectroscopy has been used to investigate the average oxidation state of Cr in both electrochemically and chemically delithiathed Li5/3−x Ti7/3CrO7. The O K edge, Ti L2,3 and Cr L2,3 edge were monitored. Upon removal of Li ions, the oxygen K edge shows a continuous change while the Cr L edges remain almost unchanged. The Cr 2p multiplet was compared with reference samples (Cr2O3, CrO2 and K2Cr2O7) in order to assess on the sensitivity of the Cr L-edge to the oxidation state of chromium ion. The similarity between the Cr L spectra of Cr2O3 and CrO2 makes the valence analysis difficult in Li5/3−x Ti7/3CrO7 but the presence of CrVI is excluded in oxidized samples. However, evolution of the low energy loss spectra observed in the 10–15eV region confirms the modification of the electronic structure and partial oxidation of CrIII to CrIV. [Copyright &y& Elsevier]