We performed Raman spectroscopy of Co-doped Li2O (CDL), a cathode material for lithium-ion batteries. During the charge process of CDL, the spectra showed a new peak at 790 cm(-1), assignable to peroxide. The charge range where the peak was observed coincided with the range where oxygen gas was generated from the reaction of the charged CDL with water using platinum as catalyst. The peak was reduced and disappeared during discharge. This indicated the formation/ decomposition of peroxide in CDL during charge/discharge.