The Research On Synthesis With Solid-state Method And Electrochemical Properties Of Li₃V₂（PO₄）₃

Lithium vanadium phosphate Li3V2(PO4)3with polyanion structure is a promising candidate cathode material for lithium ion batteries. It has attracted much attentions due to the stable structure, excellent electrochemical performance, high safety and environment friendly. However, the poor intrinsic electronic conductivity of Li3V2(PO4)3,limits its practical application. This paper improves the electrochemical performances of Li3V2(PO4)3by coating carbon on the base of optimizing the technological conditions. The results show that:1.The predecomposition conditions of Li3V2(PO4)3were optimized by the orthogonal method. The results showed that,the influencing degree order of the predecomposition conditions on the discharging capacity in the second cycle from big to small were predecomposition temperature, predecomposition time, flow rate of protection gas and milling time. The best combination of the technological conditions was as follows:the ball milling time was3h, the predecomposition temperature was350℃, the predecomposition time was5h and the flow rate of protection gas was100mL/min. The discharge capacity of sample prepared was121.4mAh/g and the Coulombic efficiency was98.86%.2.The synthesis conditions of Li3V2(PO4)3prepared by solid-state method was optimized systematically. The results showed that:the sample possessed well-developed crystallite structure, uniformly distributed particles and small particles, When the synthesis temperature was800℃and the synthesis time was16h. The initial discharge capacity was124.4mAh/g at the0.2C rate and the discharge capacity decreased to121.3mAh/g after30cycles. Its cyclic performances was excellent. The initial discharge capacity was126.9mAh/g at the0.2C rate when the Li/V molar ratio was3.05:2.0and the discharge capacity was126.0mAh/g and the capacity retention rate was99.29%after30cycles. The best combination of the synthetic conditions was as follows:the synthesis temperature was800℃, the synthesis time was16h, the Li/V molar ratio was3.05:2.0.3.Li3V2(PO4)3cathode material was prepared by high temperature solid-state method and modified by carbon coating, which acetylene black, glucose, epoxy resin and phenolic resin were used as carbon sources. The results showed that the prepared Li3V2(PO4)3possessed well-developed monoclinic and crystallite structure. The size of sample which was prepared by using phenolic resin as carbon source at the mass content of5wt%was small and the performances was best. The initial discharge capacity were129.1mAh/g and103.9mAh/g at0.2C and5C. The value of charge transfer resistance was as low as59.04Ω.