(217ch) Preparation and Characterization of Carbon-Coated Silicon Nano-Composites As Anodes for Lithium-Ion Batteries

Silicon is a potential material to replace graphite as an anode in Li-Ion batteries because of its high theoretical capacity. However, the major barriers to commercialization are volume expansion for lithium insertion/extraction and intrinsically low conductivity of bare silicon particles, result in poor rechargeability and mechanical instability during cyclic charge/discharge of Li-Ion batteries. In this study, an effective and low-priced method to produce carbon-coated silicon nano-composites as a high-capacity anode material for rechargeable lithium-ion batteries has been investigated. Initially, nanosized silicon particles (<500 nm) mixed in a citric acid solution via ultrasonication was prepared by thermal treatment in inert gas at elevated temperature (400-800 °C) to form a homogeneous carbon-coated layer onto the surface of the silicon nanoparticles. The effects of the processing temperature, the duration of thermal treatment, silicon particle size, and the mass ratio of citric acid to silicon were investigated in detail. All of these parameters definitely influence the cyclic charge/discharge performance of the carbon-coated Si nanocomposites. Carbon-coated Si nano-composites in nitrogen gas at 400 °C show the better cycling performance, with a capacity loss of less than 0.9% per cycle and retaining a specific capacity of 1800 mAh/g beyond 31 cycles, which is much better than the graphite anode. Furthermore, the capacity fading and lithiation mechanisms of silicon and carbon-coated silicon particles also been studied in this study by cycling tests and electrochemical impedance spectroscopy (EIS) analyses, respectively. The dimensional stability of the Si nanoparticles provided by the carbon nano-coating enhances the electric contact of silicon particles and it seems to be the leading reason for this observably enhanced electrochemical performance.