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 Ni²⁺/Ni⁴⁺and tunable structures. However, they suffer from surface oxygen loss at high charge voltages for interface degradation. Herein, the surface electronic structure of Na_0.9Ni_0.32Cu_0.08Fe_0.1Mn_0.3Ti_0.2O₂is 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^–1and an energy density of 140 Wh kg^–1in 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.