Local Electronic Structure Regulation To Consolidate Surface Oxygen of Layered Oxide Cathodes in Sodium-Ion Batteries

Nickel-based layered oxide materials are promising cathodes for sodium-ion batteries (SIBs) due to the two-electron reactions of Ni 2+ /Ni 4+ and tunable structures. However, they suffer from surface oxygen loss at high charge voltages for interface degradation. Herein, the surface electronic structure of Na 0.9 Ni 0.32 Cu 0.08 Fe 0.1 Mn 0.3 Ti 0.2 O 2 is tuned via secondary annealing to consolidate its surface oxygen for the rock-salt phase. It lowers the O 2p state and enhances the covalent interactions between transition metal (TM) and O, leading to reduced surface oxygen redox activity and suppressing its release. This favors the construction of a uniform and compact cathode–electrolyte interface (CEI) layer to prevent electrolyte degradation. The as-synthesized oxide material delivers a high specific capacity of 146.1 mAh g –1 and an energy density of 140 Wh kg –1 in pouch cell with a hard carbon anode, along with excellent stability to retain 92% of its initial capacity after 500 cycles. This investigation provides insights to interface design for high-performance cathode materials of SIBs.