Morphological engineering and gradient architecture of O3-Type NaNi1/3Fe1/3Mn1/3O2 cathodes for sodium-ion batteries: Synergistic modulation of wide-temperature adaptability and air stability

The pursuit of high-performance, air-stable cathode materials presents a critical challenge for sodium-ion battery commercialization. While morphological engineering offers property modulation, conventional homogeneous designs fundamentally limit the balance between reactivity and structural stability. This work employs a coprecipitation-based approach to innovatively integrate morphological control and compositional gradient design, constructing a cubic O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM-3) cathode with a nickel-rich core/manganese-rich shell architecture. Benefiting from the superior kinetics of cubic particles and the synergistic effects of gradient structure on Na⁺ transport, surface passivation suppression, and transition metal stabilization, NFM-3 achieves breakthrough performance across a broad temperature range (−20 to 70 °C) and under air exposure conditions. At 25 °C and 0.1 C (2.0–4.0 V), it delivers an initial discharge capacity of 145.2 mAh·g⁻¹ with 82.2 % capacity retention after 500 cycles at 1 C, while maintaining 87.3 mAh·g⁻¹ at a high rate of 10 C. At a low temperature of −20 °C, the material retains a discharge capacity of 126.9 mAh g⁻¹ with 85.5 % capacity retention. At an elevated temperature of 70 °C, the corresponding values are 141.4 mAh·g⁻¹ and 22.5 %, respectively. Notably, after 30-day exposure to ambient conditions, NFM-3 preserves 93.4 % initial capacity while sustaining post-exposure cyclability (75.7 %) and high-rate capability (74.9 mAh·g⁻¹ at 10 C). This work establishes a pioneering pathway toward highly reversible and environmentally resilient SIB cathodes.