Improved sodium storage properties of Zr-doped Na3V2(PO4)2F3/C as cathode material for sodium ion batteries

To improve the intrinsic electronic conductivity of Na3V2(PO4)2F3 (NVPF), zirconium (Zr) was introduced into the NVPF/C compound through a carbothermal reduction reaction with citric acid as the carbon source. The effects of Zr4+ doping on the crystal structure and morphology of the as-prepared materials were analyzed. Electrochemical and kinetic properties of the samples were investigated by galvanostatic charge-discharge, CV and EIS test. It is confirmed that moderate Zr4+ doping can improve the electrochemical performance of NVPF. Among all Na3V2-xZrx(PO4)2F3/C (x = 0, 0.01, 0.05, 0.1) samples, Na3V1·95Zr0·05(PO4)2F3/C shows the best rate and cycle performance. It exhibits the highest specific capacity of 121.8 and 110.3 mAh/g at 0.2 and 10 C, respectively, and maintains a capacity retention of approximately 83.6% after 1000 cycles at 5 C. The kinetic properties results show that the excellent electrochemical performance of Na3V1·95Zr0·05(PO4)2F3/C can be attributed to the increase in electronic conductivity and ion diffusion coefficient.