Evolution of local structure around manganese in layered LiMnO2 upon chemical and electrochemical delithiation/relithiation

Mn K-edge X-ray absorption spectroscopic (XAS) analyses have been performed to probe the evolution of electronic and crystal structures of layered LiM nO2 upon chemical and electrochemical delithiation/relithiation. According to the X-ray absorption near-edge structure studies, it becomes clear that the trivalent manganese ion in LiMnO2 is significantly oxidized by acid tre atment and is not fully recovered by subsequent lithiation reaction with n- BuLi. The extended X-ray absorption fine structure results presented here d emonstrate that the local structure around manganese in LiMnO2 is changed f rom a layered alpha-NaFeO2-type structure to a spinel-like one upon chemica l delithiation reaction. It is also found from the XAS analyses for the cyc led LiMnO2 that the electrochemical charge-discharge process gives rise not only to the partial oxidation of manganese ion but also to the migration o f Mn into the interlayer lithium site, resulting in the coexistence of the layered structure and the spinel one. Such results highlight the lattice in stability of layered manganese oxide for the chemical and electrochemical e xtraction of lithium, which is responsible for the remarkable capacity fadi ng and the formation of two plateaus at around the 3 and 4 V regions after the first electrochemical cycle. On the basis of the present experimental f indings, we are now able to suggest that the electrochemical performance of layered LiMnO2 can be improved by blocking the Mn migration path through c ationic substitution.