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

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.