Effect of Ni doping on electrochemical performance of Li3V2(PO4)3/C cathode material prepared by polyol process

Li3V2−xNix(PO4)3/C (x=0, 0.05, 0.1, and 0.2) composite was prepared by a fast liquid phase polyol method. The effect of Ni doping on the structure, morphology and electrochemical performance of Li3V2(PO4)3/C was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. The XRD analysis showed that a small amount of Ni doping does not alter the crystal structure of Li3V2(PO4)3/C cathode material, and the crystal size of the composites increased slightly with the increase of Ni doping. In the potential range of 3.0–4.3 V, the Li3V2−xNix(PO4)3/C (x=0.1) composite showed the highest discharge capacity of 128 mAh g−1 at 0.1C, which is close to the theoretical capacity. The discharge capacity of the sample was stable even after the 20th cycles. According to the results from cyclic voltammetry (CV) measurements, electrochemical behavior of the optimal sample has no change after 100 cycles at 2C rate, indicating the structural stability of the prepared composite. The EIS measurements indicate that the doping with an appropriate amount of Ni decreases the charge transfer resistance, which is favorable for the insertion/extraction of Li+. The improved electrochemical performance of the samples can be attributed to the appropriate amount of Ni doping and carbon and porous structure that enhanced electrical conductivity and structural stability, respectively.