Water and Carbon Dioxide‐Resistant Cathode With Radial Phase and Valence Gradient Distribution via Composition Regulation

ABSTRACT Regulating the composition and valence states of layered O3‐phase sodium‐ion battery cathode materials can effectively mitigate issues related to complex phase transitions and poor air stability. However, further research is needed to optimize the controllable design of these structures and to better understand the transition mechanisms between different hierarchical phases. Herein, precise regulation of radial sodium‐ion concentration, phase structure, and transition metal average valence of P/O cathode was realized through precursor‐based secondary heterogeneous coprecipitation and solid‐state sintering. Radial scanning transmission electron microscopy and electron energy loss spectroscopy characterization confirmed elemental migration during sintering, resulting in a gradient distribution of sodium content, phase structure, and transition metal valence states. This radially gradient continuous P2/O3–O3 composite without obvious phase interface reduces the barrier of sodium‐ion transport at the phase interface to mitigates volume changes from O3–O3′ phase transitions, inhibits Na + /H + exchange and acid erosion, and enhances moisture/carbon dioxide resistance, kinetic performance, and cycling stability. Consequently, after 10 h of exposure to 82% humidity and 3330 ppm CO 2 concentration, the first‐cycle charge capacity of designed NM + 0.4 μm was 103.8 mAh g −1 , while the capacity loss reduced from 50.12% to 12.35%. This study presents a novel approach to enhancing the stability of layered cathode materials for sodium‐ion batteries.