Robust Surface [BO3] Gradient Integration: Nanoscale Engineering for Enhanced Environmental Stability of Sodium Layered Cathodes

Sodium-ion batteries offer promise for large-scale energy storage, yet the environmental sensitivity of layered cathode materials significantly hinders commercialization. Current strategies often fail to simultaneously address water intercalation and cation exchange while maintaining electrochemical performance. Here, we demonstrate a nanoscale surface engineering approach through the formation of a precisely controlled ∼20 nm [BO3] gradient on layered oxide cathode surfaces. This gradient integration creates a protective interface by coordinating with [MnO6] polyhedra at the material surface, as confirmed by EELS analysis and DFT calculations. The surface-modified P2-Na0.67Mn0.88Al0.12B0.05O2 (NMABO) cathodes deliver 176 mAh g-1 initial capacity at 0.2C and 80.1% retention after 1000 cycles at 10C. Crucially, the engineered interface enables exceptional moisture resistance in NMABO with 80.3% capacity retention after 1300 cycles following 14-day air exposure and shows minimal capacity loss after 2-year storage under controlled conditions. Mechanistic investigations reveal that the [BO3] gradient simultaneously inhibits Jahn-Teller distortion and creates energetic barriers against H2O intercalation and Na+/H+ exchange. The strategy's universality is further validated on commercial O3-NaNi1/3Fe1/3Mn1/3O2 cathodes, which demonstrate robust stability in humid air and confirm superior acid and oxidation resistance. This work establishes a scalable approach for enhancing the environmental stability of sodium layered oxides through rational nanoscale interface design, addressing the fundamental degradation in ambient conditions.