Electron transfer in LiMn1.5Ni0.5O4 during charging studied with soft X-ray spectrometry

Abstract

This is the first report on analyzing the chemical state of Li-ion battery electrodes at different states of charge by using a wavelength-dispersive spectrometer, which has a two-order improved energy resolution in the soft X-ray energy region compared with that of a conventional energy-dispersive X-ray analyzer. Electrodes containing LiMn 1.5 Ni 0.5 O 4 were charged to prepare Li 0.5 Mn 1.5 Ni 0.5 O 4 and λ-Mn 0.75 Ni 0.25 O 2 . The soft X-ray emission spectra obtained from those materials show that the O-K emission signal was drastically decreased throughout the charging process. This suggests that O-2p electron contributed to the electrochemical oxidation. The density of states and Bader charge evaluated from ab initio calculation support this result.