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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]

Abstract: In the search for new electrodes for lithium batteries processing under high pressure opens new paths to innovative materials. The High Pressure (HP) polymorph of α-FePO4 crystallizes in the CrVO4 structural-type; first principles calculations predict that Li insertion would occur at 3.36V. Accordingly, crystalline samples of HP-FePO4 display electrochemical activity with a lithium insertion process occurring at 3V, which has not been observed in the α-FePO4 polymorph. This reduction process is characterized by a large cell polarization that suggests a very slow kinetics. The poor electrochemical performance of highly crystalline HP-FePO4 is favored in iron phosphate samples obtained under mild conditions of pressure and temperature, that produce a partially amorphous material and prevent an excessive particle growth. [Copyright &y& Elsevier]