Synergistic Perovskite Titanate Coating and Lattice Doping Toward Air‐Stable and Long‐Life O3‐Type NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ Cathodes

ABSTRACT O3‐type layered oxides are promising cathode materials for sodium‐ion batteries but suffer from structural instability, sluggish kinetics, and moisture sensitivity. This work proposes a synergistic modification of O3‐NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ (NFM). Among various perovskite titanates (CaTiO ₃ , SrTiO ₃ , BaTiO ₃ ) investigated, CaTiO ₃ proves to be the most effective modifier. DFT calculations reveal that Ca ²⁺ doping uniquely strengthens the Na‐O interaction, fundamentally enhancing the air stability. The conformal CaTiO ₃ coating serves as a robust physical barrier against humid air, significantly suppressing the formation of surface carbonates and residual alkali. Simultaneously, Ca ²⁺ and Ti ⁴⁺ are doped into Na and transition metal (TM) sites, respectively, which enlarges the Na ⁺ layer spacing (from 3.701 to 3.812 Å), strengthens the TM─O framework, and mitigates irreversible phase transitions. As a result, the modified NFM@CTO06 cathode exhibits outstanding electrochemical performance, demonstrating a high capacity retention of 85.1% after 300 cycles at 1 C. Furthermore, it demonstrates reduced voltage hysteresis, enhanced Na ⁺ diffusion kinetics, and significantly improved air stability. This surface‐to‐bulk strategy offers a feasible approach toward practical high‐energy‐density sodium‐ion batteries.