Nominal Na0.6(Li0.2Mn0.8)O2 with the layered P3 structure (s.g. R3m) showed XPS evidence of holes in the O-2p bands on removal of Na+ ions. A large voltage plateau at 4.1 V versus Na+/Na faded significantly over 50 cycles although the capacity in the range 20 ≤ V < 4.5 V remained unchanged. Oxidation of the O-2p bands is not reversible.
