Structure of the high voltage phase of layered P2-Na2/3−zMn1/2Fe1/2O2 and the positive effect of Ni substitution on its stability

Using in-depth structural and spectroscopic analysis, we unravel the nature of phenomena specific to the Fe 3+ /Fe 4+ redox couple in P2-Na 0.67− z Ni y Mn 0.5+ y Fe 0.5−2 y O 2 .