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

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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.