Reversible Electron–Holes on O in P2‐type Na 0.67 Li 0.1 Ni 0.3 Mn 0.6 O 2

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 Mn 3+/4+ capacity close to 2 V vs Na + /Na. Here, a new Na‐ion cathode exhibiting electron–holes on O is demonstrated, P2‐type Na 0.67 Li 0.1 Ni 0.3 Mn 0.6 O 2 , which also utilizes the high voltage Ni 3+/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 Na 0.67 Li 0.1 Ni 0.3 Mn 0.6 O 2 over cycling.