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 Na 3 V 2 (PO 4 ) 2 F 3 (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 Zr 4+ 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 Zr 4+ doping can improve the electrochemical performance of NVPF. Among all Na 3 V 2-x Zr x (PO 4 ) 2 F 3 /C (x = 0, 0.01, 0.05, 0.1) samples, Na 3 V 1·95 Zr 0·05 (PO 4 ) 2 F 3 /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 Na 3 V 1·95 Zr 0·05 (PO 4 ) 2 F 3 /C can be attributed to the increase in electronic conductivity and ion diffusion coefficient .