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The effect of mechanical grinding on the electrochemical properties of Li2Ti3O7 regarding lithium insertion is studied. X-ray diffraction experiments of milling compounds showed a progressively amorphization of the crystalline material due to both crystalline size decreasing and internal strain increasing. These structural modifications are reflected in the electrochemical behavior of Li2Ti3O7, when it is used as the positive electrode in lithium cells. As a function of milling time a higher specific capacity is obtained during the first discharge of the cell, but when charging an increasing in the irreversible capacity is observed. The most promising Li2Ti3O7 based electrode has been achieved, under our experimental conditions, for 13 hours milling that produces a compound with crystallite size of approximately 20 nm. [ABSTRACT FROM AUTHOR]

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: 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]