In the following discharge process, the X phase transforms to the P3 phase at about To identify changes in the valence states of Ni and Mn during charging and discharging, ex-situ X-ray absorption near edge structure (XANES) analysis was performed at the Ni and Mn K-edges for O3-NaNMO, O3-NaMNMO, and O3-NaSNMO during the first cycle.