Charge/discharge mechanism of a new Co-doped Li2O cathode material for a rechargeable sealed lithium-peroxide battery analyzed by X-ray absorption spectroscopy

Soft X-ray absorption spectroscopic studies are carried out to clarify the charge/discharge reaction mechanism of Co-doped Li2O (CDL, Co/Li = 0.1 molar ratio) as a cathode material for a new rechargeable lithium-peroxide battery. Upon charging CDL in an aprotic electrolyte, a drastic change can be seen in the O K-edge spectra, with a new, strong peak assignable to σ*(O-O) of peroxide at photon energy of 531.0 eV. This peak is reduced during subsequent discharging, causing the spectrum to essentially return to that of pristine CDL recorded in total fluorescence yield mode. The Co L2,3-edge spectra do not show a remarkable change during charging, with the exception of the disappearance of a Co2+ shoulder peak. The spectrum of charged CDL is in reasonable agreement with the calculated spectrum, assuming that the fraction of Co3+-L (where L indicates a hole state in the oxygen 2p band) is dominant in the electronic configuration of the ground state. This suggests that, to a certain extent, a redox reaction involving a ligand hole state (Co3+-L) participates in generation of the capacity.