Regulating Phase Stability of O3-Type-Layered Oxide Cathode via Zn²⁺ Substitution

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O3-type-layered oxides have gained recognition as highly promising cathode materials for rechargeable sodium-ion batteries, offering superior cyclical sodium compatibility, higher theoretical capacity, and desirable initial Coulombic efficiency than their P2-type counterparts. However, their practical utilizations are often impeded by inherent structural instability and irreversible O3–P3 phase transition, leading to rapid capacity deterioration and limited lifespan. In this study, a transition cation (Zn 2+ )-doped O3-type Na[Zn 0.05 (Ni 1/3 Fe 1/3 Mn 1/3 ) 0.95 ]O 2 (Zn 0.05 -NNFMO) was synthesized via a facile sol–gel method, which demonstrated a high reversible capacity of 116.3 mA h g –1 with superior capacity retention. The expanded interplanar space of Zn 0.05 -NNFMO enhances the Na + diffusion kinetics and reduces the charge-transfer resistance. Moreover, Zn 2+ doping significantly mitigates irreversible phase transitions and lattice distortion caused by the Jahn–Teller effect, thereby contributing to improved structural stability and longevity. This study provides a feasible strategy for constructing stabilized O3-type-layered oxides and high-performance sodium-ion batteries.