Reversible Electron–Holes on O in P2‐type Na0.67Li0.1Ni0.3Mn0.6O2

Achieving reversible O‐redox through the formation of electron–holes on O could hold the key to a new generation of high energy density Na‐ion cathodes. However, to date, it has only been demonstrated in a small handful of cathode materials and none of these materials exploit the dual benefit of high voltage transition metal redox and O‐redox, instead relying on Mn3+/4+ capacity close to 2 V vs Na+/Na. Here, a new Na‐ion cathode exhibiting electron–holes on O is demonstrated, P2‐type Na0.67Li0.1Ni0.3Mn0.6O2, which also utilizes the high voltage Ni3+/4+ redox couple to deliver the highest reported energy density among this class of compound. By employing a low Li content and avoiding honeycomb ordering within the transition metal layer, it is possible to stabilize the hole states, and the high voltage plateau is preserved in Na0.67Li0.1Ni0.3Mn0.6O2 over cycling. Oxidation of oxide ions in transition metal oxide battery cathodes can increase the energy density, but this often results in the formation of trapped O2 and voltage loss. Here, O2 is suppressed and electron–holes on O are promoted by avoiding honeycomb ordering within the transition metal layer of Na0.67Li0.1Ni0.3Mn0.6O2. Reversible O‐redox in combination with Ni3+/4+ redox, leads to a high voltage, 500 Wh kg‐1 cathode for Na‐ion batteries.