Porous Si-C Composite As High-Performance Anode Material for Li-Ion Batteries

Abstract

Li-ion batteries (LIBs) have received widespread recognition as power sources for various potable electronics, electric vehicles, and large-scale energy storage systems. To meet ever-increasing demand for energy storage, it is necessary to develop next generation anode materials with a high capacity. Carbon-based materials are widely used as anodes for LIB and however, the theoretical capacity for graphite (372 mAh g–1) is limited due to its intercalation chemistry. Si has been considered as one of the most promising next generation materials as LIB anodes to replace commercial graphite because of its outstanding theoretical gravimetric capacity of 3580 mAh g–1 (for Li15Si4 phase), which can be obtained through the electrochemical alloying reaction with Li ion. Currently, the main challenges for using Si-based active materials are structural transition, low electrical conductivity, and unstable solid electrolyte interphase (SEI) formation caused by the large volume change (~400%) during alloying and dealloying cycle and irreversible side reactions with electrolyte. The large volume changes lead to the pulverization of electrode materials, resulting in degradation of capacity upon cycling. To overcome these drawbacks, many researches have been performed and various strategies have been proposed in terms of structural aspects such as hollow sphere, core-shell structure, and porous structure. In this study, porous Si-C composites were prepared through a simple annealing method of commercial amorphous silica (a-SiO2) and magnesium silicide (Mg2Si). Then, a chemical wet etching process was performed to remove formed magnesium oxide (MgO) and a carbon layer coating was finally carried out. The prepared material exhibited high reversible capacity and good cycle performance with very high initial coulombic efficiency. The enhanced electrochemical properties can be attributed to the porous structure with thin carbon coating.