Synthesis And Electrochemical Performance Of Lithium Battery Cathode Materials For Lithium Vanadium Phosphate

Li3V2(PO4)3 with NASICON structure which has high operating voltage, large theoretical capacity, high reversible capacity is thought to be a promising cathode material. However, the poor electrical conductivity and slow lithium ion diffusivity hinder the large-scale application of this material. Therefore, it is need to do some modification of this material. In this paper, the precursor was prepared by ball milling and the porous Li3V2(PO4)3/C was synthesized by high temperature carbon-thermal reduction method. The effects of calcination temperature, calcination time and the quantity of oxalic acid on the performance of material and the kinetics of the electrode were studied in detail, and the main contents are summarized as follows:The bulk Li3V2(PO4)3/C samples were synthesized by high temperature carbon-thermal reduction method with starch, phenolic resin, glucose as carbon source, respectively. The results show that the Li3V2(PO4)3/C sample which prepared with starch as carbon source had the best electrochemical performance. The initial discharge capacity at 0.1C was 109.5 mAh g-1 and the discharge capacity was 100.5 mAh g-1 after 30 cycles, the capacity retention rate was 91.8%. It indicated that starch was an ideal carbon source for Li3V2(PO4)3/C.The porous Li3V2(PO4)3/C composite was synthesized by oxalic acid assisted carbon thermal reaction, and the effects of calcination temperature, calcination time and the quantity of oxalic acid on the peformance of material were investigated. The results showed that:When nV2O5:nH2C2O4= 1:6 and the precursor was calcined at 800℃for 10 h, the synthetic material had optimal physical and electrochemical performance. The porous Li3V2(PO4)3/C composite was monoclinic structure with space group of P21/n. The sample had an excellent electrochemical performance:the initial discharge capacity at 0.1 C was 130.0 mAh g-1, and the discharge capacity was still 124.9 mAh g-1 which was 96.1% of the initial discharge capacity after 20 cycles, even at 2 C, the discharge capacity was still 91.5 mAh g-1 after 50 cycles, the capacity loss was only 7%. The electrode process kinetics of the porous Li3V2(PO4)3/C was studied by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). CV analysis indicated that the range of the solid diffusion coefficient and liquid diffusion coefficient of the porous Li3V2(PO4)3/C at various potential were 1.004×10-9cm2 s-1～1.540×10-8 cm2 s-1 and 1.022×10-7cm2 s-1～2.709×10-7cm2 s-1, The Li-ion diffusion coefficient calculated by EIS range from 2.978×10-11 cm2 s-1 to 1.885×10-8 cm2 s-1. The results showed that this electrode was good at insertion/de-insertion of Li+...