A novel NASICON-typed Na3V1.96Cr0.03Mn0.01(PO4)2F3 cathode for high-performance Na-ion batteries

Na3V2(PO4)(2)F-3 (NVPF) with a NASICON structure has attracted widespread attention as a cathode material for sodium-ion batteries due to its stable 3d open framework, high operating voltage, and high theoretical energy density. However, this material faces limitations in practical applications due to its inherently low intrinsic electronic conductivity and the high cost of vanadium. In this study, we substituted vanadium with low-cost elements and synthesized a series of NVPF cathode materials with varying levels of Cr/Mn doping using a simple sol-gel method. The optimal NVPF-Cr/Mn1 cathode exhibits discharge specific capacities of 119.7 mAh g(-1) at 1C and 109.8 mAh g(-1) at 10C. Additionally, the discharge specific capacity of NVPF-Cr/Mn1 is 106.9 mAh g(-1), with a capacity retention rate of 80 % after 400 cycles. These performance improvements are attributed to the synergistic effect of co-doping with chromium (Cr) and manganese (Mn): they expand the channels for sodium ion transport within the lattice, reduce the material's impedance and polarization, enhance the kinetics of sodium ion diffusion reactions, effectively prevent lattice distortion, and significantly improve long-term cycling performance. By strategically designing NASICON-type cathodes and employing multi-metal ion substitutions to regulate composition, we not only enhance the battery's cycle life but also contribute to reducing the cost of electrode materials. This approach opens up new possibilities for practical applications in the field of energy storage.