Si/BiPO4 composite anode material for lithium ion batteries prepared by solvothermal method

Abstract

Lithium ion batteries play an important role in various energy storage technologies due to their good safety performance. As an anode material, silicon has attracted attention for its higher theoretical capacity than commercial graphite. But large volume expansion and unstable solid electrolyte interface (SEI) during the cycling of silicon lead to rapid capacity decay, which limits the commercial application of silicon anode. In this article, Si/BiPO4 anode materials were prepared by solvothermal reaction. After morphology analysis and constant current charge discharge cycle analysis of Si/BiPO4 anode materials with different mass ratios, it was found that Si/BiPO4 anode materials with the mass ratio of 7:3 exhibited more excellent electrochemical performance. The conversion reaction of BiPO4 and Li generates Bi and Li3PO4, and the alloying reaction of Bi generates Li3Bi. Bi and Li3Bi reduce the internal resistance of the Si/BiPO4 composite, and Li3PO4 is distributed on the surface of Si material, participating in the formation of SEI film and improving the stability of the material. At a current density of 500 mA g−1, the first discharge specific capacity of the Si/BiPO4 anode is 2672.1 mA h g−1. After 200 cycles, the discharge specific capacity remains at 1308.9 mA h g−1. The electrochemical impedances of pure Si and Si/BiPO4 anode materials before and after cycling were analyzed. It was found that the resistance of the Si/BiPO4 anode before and after 100 cycles was lower than that of pure Si materials, which further proved that the addition of BiPO4 material helps to improve the charge transfer ability of pure silicon materials.