A High-Entropy Strategy to Enhance the Structure and Electrochemical Performance of NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ Cathodes

Layered oxide cathode materials for sodium-ion batteries, particularly NaNi1/3Fe1/3Mn1/3O2 (NFM), have garnered significant interest due to their cost-effectiveness and moderate specific capacity. However, their practical application is severely limited by poor air stability and phase transitions along with structural instability during cycling. Inspired by the concept of high-entropy doping, this study introduces both Mg2+ and Ti4+ into the transition metal layer of the NFM material. The interlayer spacing is expanded, and the Na+ transport channels are widened, thereby facilitating rapid sodium-ion diffusion. Furthermore, the introduction of Ti and Mg elements, which exhibit strong interactions with oxygen, enhances the structural stability of the material through synergistic effects among the multielement components. Consequently, the designed NFMTM-10 exhibits superior electrochemical performance. NFMTM-10 achieves an initial Coulombic efficiency as high as 97.5% and a high capacity retention of 80.24% after 100 cycles at 0.1 C. This work demonstrates the feasibility of simultaneously optimizing sodium-ion transport kinetics and crystal structure stability through multielement high-entropy doping design, providing a perspective for developing high-performance sodium-ion battery cathode materials.