Enhancing High-rate Cycling Capability of Sodium-Ion Batteries at High Temperatures through Cathode Structural Design and Modulation

Abstract

Sodium-ion batteries (SIBs), as a promising energy storage technology, offer the advantages of cost-effectiveness and abundance of source materials. However, insufficient thermal stability at elevated temperatures remains a significant challenge for their commercialization. This study aims to enhance the high-temperature thermal stability of SIBs cathode materials through rational structural design and ion doping strategies. The gradient-directed diffusion technique optimizes the calcination process, adjusting the concentration gradient distribution within the material. This approach increases sodium layer spacing and cell volume, improving thermal stability and electrode kinetics under high-rate cycling conditions. On this basis, a copper-iron dual doping strategy is applied further to enhance the cathode's crystal structure and electrical conductivity, reducing side reactions with the electrolyte. Experimental results show that the optimized and doped P2-Na_0.67Mn_0.55Ni_0.30Fe_0.05Cu_0.10O₂ materials exhibit excellent capacity retention at high temperatures, with 87.8% retention after 200 cycles at 10 C and 60°C in half-cell tests. In full-cell configurations, the materials retain 81.7% of their initial capacity after 100 cycles at 5 C and 60°C, while exhibiting near-zero strain characteristics (0.86%). The first principle calculations reveal that NMNCF-2 enhances electrical conductivity, sodium-ion migration rate, and cycling stability by narrowing the band gaps and reducing the migration energy barrier. These findings provide a robust solution for the high-temperature applications of SIBs, demonstrating the potential of structural optimization and ion doping to improve performance and safety significantly.