Si(-silicide) embedded in highly elastic exfoliated graphite nanocomposite anode materials produced by high-energy mechanical milling for lithium-ion secondary batteries

Abstract

Silicon-based nanocomposite materials have attracted noteworthy attention as a potential anode material for the lithium-ion rechargeable batteries. However, volume changes of the Si during the lithiation/delithiation result in inferior capacity retention and poor coulombic efficiency. In this work, we report a novel nanocomposite Si-FeSi2/EG in which nano-scale Si-FeSi2 powders encapsulated in the exfoliated graphite (EG) synthesized by a scalable two-stage high-energy mechanical milling. Structure and microstructure of the nanocomposite are investigated by XRD, FE-SEM, and HR-TEM. The morphology of the Si-FeSi2/EG nanocomposite reveals the random distribution of Si-FeSi2 in the EG. The nano-indentation results revealed that the Si-FeSi2/EG electrode exhibited significant elastic recoverable energy as compared to the Si and the Si-FeSi2. Remarkably, the Si-FeSi2/EG nanocomposite demonstrates a stable reversible capacity of ∼1002 mAh g−1 even at 50th cycle with a coulombic efficiency ∼99.8%. The irreversible capacity loss of Si-FeSi2/EG anode after the 1st, 3rd and 50th cycle was 21, 2.2 and 0.2, respectively. The significant cyclic performance was mainly ascribed to the silicon crystal size reduction and highly elastic Si-FeSi2/EG nanocomposite due to encapsulation of the Si-FeSi2 in the exfoliated graphite.