Research on the Phase Transformation of Silicon Anode Material for Lithium Ion Batteries by Constant-Capacity Discharging

Silicon is the most attractive anode candidate for lithium ion batteries for its high theoretical capacity. However, it is difficult to be applied as anode material of lithium ion batteries for its poor cyclability and high irreversible capacity caused by structure collapse during the course of lithium insertion-extraction. Considering finding an efficient way to alleviate the crystal transformation during lithium insertion, the silicon anode with the highest theoretical capacity of all know non-lithium substances, was discharged by controlling its insertion capacity. The phase transformation during lithium ion insertion into silicon was investigated in detail. The lithium-insertion phases produced by constant capacity processing consist of Li-Si binary crystals and amorphous host phase. A stable Li12Si7 phase was found under different discharge conditions. This Li-Si binary phase formed by constant capacity showed high structure-reversibility during lithium insertion-extraction. The enhanced cyclability of silicon anode during constant-capacity discharging benefits from the mixture phases of silicon amorphous and crystal Li-Si alloy.