The role of Li2MO2 structures (M=metal ion) in the electrochemistry of (x)LiMn0.5Ni0.5O2 • (1-x)Li2TiO3 electrodes for lithium-ion batteries

The electrochemical reactions of lithium with layered composite electrodes (x)LiMn0.5Ni0.5O2 . (1 - x)Li2TiO3 were investigated at low voltages. The metal oxide 0.95LiMn(0.5)Ni(0.5)O(2) . 0.05Li(2)TiO(3) (x = 0.95) which can also be represented in layered notation as Li(Mn0.46Ni0.46Ti0.05Li0.02)O-2, can react with one equivalent of lithium during an initial discharge from 3.2 to 1.4 V vs. Li-0. The electrochemical reaction, which corresponds to a theoretical capacity of 286 mAh/g, is hypothesized to form Li-2(Mn0.46Ni0.46Ti0.05Li0.02)O-2 that is isostructural with Li2MnO2 and Li2NiO2. Similar low-voltage electrochemical behavior is also observed with unsubstituted, standard LiMn0.5Ni0.5O2 electrodes (x = 1). In situ X-ray absorption spectroscopy (XAS) data of Li(Mn0.46Ni0.46Ti0.05Li0.02)O-2 electrodes indicate that the low-voltage (<1.8 V) reaction is associated primarily with the reduction of Mn4+ to Mn2+. Symmetric rocking-chair cells with the configuration Li(Mn0.46Ni0.46Ti0.05Li0.02)O-2/Li(Mn0.46Ni0.46Ti0.05Li0.02)O-2 were tested. These electrodes provide a rechargeable capacity in excess of 300 mAh/g when charged and discharged over a 3.3 to -3.3 V range and show an insignificant capacity loss on the initial cycle. These findings have implications for combating the capacity-loss effects at graphite, metal-alloy, or intermetallic negative electrodes against lithium metal-oxide positive electrodes of conventional lithium-ion cells. (C) 2002 Published by Elsevier Science B.V.