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 0.95LiMn0.5Ni0.5O2·0.05Li2TiO3 (x=0.95) which can also be represented in layered notation as Li(Mn0.46Ni0.46Ti0.05Li0.02)O2, can react with one equivalent of lithium during an initial discharge from 3.2 to 1.4 V vs. Li0. The electrochemical reaction, which corresponds to a theoretical capacity of 286 mAh/g, is hypothesized to form Li2(Mn0.46Ni0.46Ti0.05Li0.02)O2 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)O2 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)O2/Li(Mn0.46Ni0.46Ti0.05Li0.02)O2 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. Keywords: Lithium batteries, Layered cathodes, Lithium manganese nickel oxide