High performance of Bi3+ and Cl− co-doped Li3V2(PO4)3 as cathode for lithium-ion batteries

Abstract

Bismuth (III) (Bi3+) and chloride (Cl−) ion co-doped Li3V1·97Bi0·03(PO4)3−x Cl x /carbon (C) compounds (x = 0·03, 0·05, 0·07, 0·09) were prepared by way of a simple sol–gel method. The X-ray diffraction patterns proved that a small amount of bismuth (III) and chloride ion doping does not change the crystal structure of lithium vanadium phosphate (Li3V2(PO4)3). Charge/discharge results showed that bismuth (III) and chloride ion co-doped samples exhibited higher initial capacities than lithium vanadium phosphate/carbon. Li3V1·97Bi0·03(PO4)2·95Cl0·05/carbon demonstrated the highest capacity of 188 mAh/g at 0·1 C. The cycling performance at 1 C showed that the capacity retention of Li3V1·97Bi0·03(PO4)2·95Cl0·05/carbon reaches 81·31% after 300 cycles. Electrochemical impedance spectroscopy and cyclic voltammetry testing indicated that Li3V1·97Bi0·03(PO4)2·95Cl0·05 has the smallest charge-transfer resistance and the largest lithium-ion (Li+) diffusion coefficient. The improvement can be assigned to the enhanced kinetics of lithium ions, reduction in polarization and decreased charge-transfer resistance of the electrode.