Boosting cycle stability and rate capability of O3-type layered oxide cathodes through nonmetal interstitial doping and surface reconstruction for sodium-ion batteries

O3-type layered oxides have attracted widespread attention in sodium-ion batteries due to their high theoretical specific capacity. However, during electrochemical cycling, they suffer from complex phase transitions and structural degradation, leading to rapid capacity decay, which severely hinders their practical application. In this work, we propose a composite modification strategy involving boron doping coupled with surface coating to enhance the electrochemical performance of O3-NaNi_0.5Mn_0.5O₂ cathode. The introduction of BO₄ tetrahedra at interstitial sites strengthens the bonding between transition metals and oxygen, improving the crystal structure and enlarging the Na⁺ diffusion channels. After treatment with H₃BO₃, the material undergoes surface reconstruction, resulting in a uniform coating layer that effectively eliminates residual alkali and improves air stability. Therefore, the modified cathode exhibits excellent rate capability (86.5 mAh/g at 5C) and cycling stability (87.7 % capacity retention after 200 cycles at 5C). This work provides a simple and feasible composite modification approach for O3-type layered oxides, offering important guidance for the design of long-cycle cathode materials in large-scale energy storage systems.