Enhancing Structural and Interfacial Stability of NaNi1/3Mn1/3Fe1/3O2 Cathodes via Sb3+ Doping for Sodium Ion Batteries

O3-type NaNi1/3Mn1/3Fe1/3O2 (NFM) cathodes for sodium-ion batteries face critical challenges of sluggish Na+ diffusion and structural degradation during cycling. In this study, we implement an Sb3+ doping strategy that enhances structural stability and interfacial stability by modulating the NFM grain morphology to promote densification of primary particles and shorten Na+ migration paths. The optimized Sb-doped NFM1Sb (1%mol Sb) cathode exhibits excellent electrochemical performance, achieving 86.48% capacity retention after 200 cycles at 1 C and a high rate capability of 122.2 mAh g−1 at 5 C. These improvements are attributed to the alleviation of stress concentration and suppression of microcrack formation during cycling. This work demonstrates the critical role of grain morphology regulation through heavy-metal doping in developing long-life and high-rate SIBs, providing a viable pathway toward next-generation energy storage systems.