Effect of Cr3+doping on the electrochemical performance of Na3V2(PO4)2F3/C cathode materials for sodium ion battery

Na3V2(PO4)2F3 is considered as one of the most promising cathode materials for sodium-ion batteries (SIBs). However, the low electronic conductivity of this material severely restricts its electrochemical performance. Herein, Cr-doped Na3V2(PO4)2F3/C material was synthesized by a simple sol-gel method, and the effects of Cr3+ doping on the structure, morphology and electrochemical performance were systematically investigated. The optimized material Na3V2-xCrx(PO4)2F3/C (x = 0.05) exhibits high initial discharge capacity of 101.9 mAh g-1 at 10 C and keep a capacity retention of 68.7 % after 1000 cycles. The improved electrochemical performance can be attributed to the higher crystallinity, improved intrinsic electronic conductivity and sodium ion diffusion coefficient due to the doped Cr3+, which accelerates the electron transport and charge transfer rate. The opti-mized Cr-doped Na3V2(PO4)3F3/C material obtained in this work can promote the practical application of Na3V2(PO4)3F3 cathode.