Sb-Doped O3-NaNi<sub>0.3</sub>Fe<sub>0.2</sub>Mn<sub>0.5</sub>O<sub>2</sub> Cathode with\nImproved Cyclic Stability for\nSodium-Ion Batteries

As a leading sodium-ion battery cathode material, O3-type\nlayered\noxides combine excellent theoretical specific capacity and cost-effectiveness,\noffering potential solutions for the large-scale energy storage industry.\nHowever, they still struggle with significant capacity degradation\nand inferior battery performance due to the narrow Na<sup>+</sup> diffusion\nchannels and complex phase. In this paper, we introduce Sb ions into\nthe NaNi<sub>0.3</sub>Fe<sub>0.2</sub>Mn<sub>0.5</sub>O<sub>2</sub> cathode material to improve its electrochemical performance. Our\nfindings demonstrate that doping Sb results in an expansion of the\nNa layer spacing and cell volume, contributing to faster diffusion\nof Na<sup>+</sup>. Furthermore, the Na<sup>+</sup>/vacancy ordering\nand undesirable phase transition under high pressure are inhibited\nin the synthesized Na(Ni<sub>0.3</sub>Fe<sub>0.2</sub>Mn<sub>0.5</sub>)<sub>0.98</sub>Sb<sub>0.02</sub>O<sub>2</sub> cathode material,\nwhich obtains a more boosting structure and advanced electrochemical\nperformance. Within the voltage range of 2.0–4.2 V, the cathode\nmaterial possesses an initial discharge specific capacity of 127.71\nmAh g<sup>–1</sup> and maintains a capacity retention of 82.34%\n(64.33% before doping) after 100 cycles. Moreover, at a 10 C current\ndensity, a high discharge specific capacity of 90.26 mAh g<sup>–1</sup> is observed in the doped material. These results contribute essential\ninsights for the design and advancement of cathode materials for sodium-ion\nbatteries with outstanding properties.