Study On Preparation And Modification Of Li₃V₂（PO₄）₃/C Cathode Material For Lithium Ion Battery

Lithium ion battery cathode material Li3V2(PO4)3/C was synthesized by animproved sol-gel method. Citric acid is used as carbon source and complexing agent.The sample with optimum electrochemical performance can be obtained by adjustingthe pH value in the sol-gel process. Zn-doped Li3V2-xZnx(PO4)3/C (x=0,0.01,0.02,0.03) cathode materials were synthesized also by the improved sol-gel method. Thecomposition and microstructure of these composites were evaluated by XRD, SEMand HRTEM. The cathode films were made by Li3V2-xZnx(PO4)3/C (x=0,0.01,0.02,0.03) powder and then assembled into lithium batteries. The electrochemicalperformances were characterized by charge/discharge test, electrochemical impedancespectroscopy, cyclic voltammetry and potential step chronoamperometry.The electrochemical performances of Li3V2(PO4)3/C cathode materials preparedunder different pH values were evaluated. The results of galvanostaticcharge-discharge indicated that the sample prepared at pH value of4exhibits anoptimum capability at low-rate. The sample prepared at pH value of9possesses agood performance at high-rate. At1C, for example, the initial discharge capacity ofsamples prepared at pH value of4and9was131.7and125.8mAh g-1, respectively,while the initial discharge capacity of samples prepared by traditional sol-gel methodwas73.9mAh g-1. At5C, the initial discharge capacity of samples prepared at pHvalue of4and9was75.2and98.5mAh g-1, respectively, while the initial dischargecapacity of samples prepared by traditional sol-gel method was50.6mAh g-1.Zn-doped Li3V2-xZnx(PO4)3/C (x=0,0.01,0.02,0.03) cathode materials weresynthesized by an improved sol-gel method pH value was controlled at4during theprocess. It was found that Zn-doped samples were performed well at high rate. TheLi3V1.97Zn0.03(PO4)3sample exhibited the best electrochemical performance at highrates. For instance, the sample showed higher initial discharge capacity of131.5and100.7mAh g-1than those of unmodified sample (73.9and50.6mAh g-1) at1C and5C, respectively.