Unblocking Oxygen Charge Compensation for Stabilized High-Voltage Structure in P2-Type Sodium-Ion Cathode

Layered transition-metal (TM) oxides are ideal hosts for Li⁺ charge carriers largely due to the occurrence of oxygen charge compensation that stabilizes the layered structure at high voltage. Hence, enabling charge compensation in sodium layered oxides is a fascinating task for extending the cycle life of sodium-ion batteries. Herein a Ti/Mg co-doping strategy for a model P2-Na_2/3 Ni_1/3 Mn_2/3 O₂ cathode material is put forward to activate charge compensation through highly hybridized O_{2 p} TM_{3 d} covalent bonds. In this way, the interlayer OO electrostatic repulsion is weakened upon deeply charging, which strongly affects the systematic total energy that transforms the striking P2-O2 interlayer contraction into a moderate solid-solution-type evolution. Accordingly, the cycling stability of the codoped cathode material is improved superiorly over the pristine sample. This study starts a perspective way of optimizing the sodium layered cathodes by rational structural design coupling electrochemical reactions, which can be extended to widespread battery researches.