Impacts of synthesis temperature and carbon content on the electrochemical performances of the Li3V2(PO4)3/C composite synthesized by a polyol method

Abstract

As a cathode material for Li-ion battery, Li3V2(PO4)3 was synthesized by a polyol method using LiOH·H2O, V2O5, NH4H2PO4, sucrose, and ethylene glycol as starting materials. Under the polyol process, the impacts of synthesis parameters, including the sintering temperature, holding time, and carbon content, on the morphological evolution and electrochemical properties of Li3V2(PO4)3 were investigated. The XRD results show the formation of pure Li3V2(PO4)3 with monoclinic crystal structure. The images of SEM show the similar-spherical morphology with uniform and optimized particles size, which greatly improves the electrochemical performance. The carbon coated on the Li3V2(PO4)3 particles was clearly observed by electron microscopy. The particle size of Li3V2(PO4)3 powders gradually decreases with the increase of carbon content in composite. In the potential range of 3.0–4.3 V, the composite synthesized at 800 °C for 10 h with 10% carbon content shows the highest discharge capacity of 128 mAh g−1 at 0.1C, which is nearly close to the theoretical capacity, and it remains fairly stable (more than 126 mAh g−1) even after the 20th cycles. Based on the results from the electrochemical impedance spectroscopy (EIS) analysis, the apparent diffusion coefficients of Li ions in the composite materials are between 1.82 × 10−10 and 3.79 × 10−9 cm2 s−1, which are much higher than those of olivine LiFePO4.