Synthesis and electrochemical properties of Li_3V_2(PO_4)_3/C cathode material with an improved sol-gel method by changing pH value

摘要

An improved sol-gel method by changing pH value is developed to synthesize high performance Li_3V_2(PO_4)_3/C cathode material. Li_3V_2(PO_4)_3/C powders are prepared by a conventional sol-gel process without special controlling pH value and the improved sol-gel process, respectively. They are characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), galvanostatic charge/discharge test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and potential step chronoamperometry (PSCA). Not only the cycle performance for the samples prepared by the improved sol-gel method shows obvious enhancement compared with that for the sample prepared via a conventional sol-gel process, but also initial specific capacities have been improved markedly. In the voltage range of 3.0-4.8V, the sample prepared at pH value of 4 exhibits an optimum capability at low-rate. The sample prepared at pH value of 9 possesses a good performance at high-rate. The enhanced electrochemical performance can be attributed to the microstructure of the powders, which can make the lithium ion diffusion and electron transfer easier across the Li_3V_2(PO_4)_3/C interfaces, thus resulting in enhanced electrode reaction kinetics and improved electrochemical performance.