Effects of SiC and Resorcinol-Formaldehyde (RF) Carbon Coatings on Silicon-Flake-Based Anode of Lithium Ion Battery

Silicon flakes of about 100 x 1000 x 1000 nm in sizes recycled from wastes of silicon wafer manufacturing processes were coated with combined silicon carbide (SiC) and graphitic (Resorcinol-Formaldehyde (RF)) carbon coatings to serve as active materials of the anode of lithium ion battery (LIB). Thermal carbonization of silicon at 1000 degrees C for 5 h forms 5-nm SiC encapsulating silicon flakes. SiC provides physical strength to help silicon flakes maintain physical integrity and isolating silicon from irreversible reactions with the electrolyte. Lithium diffuses through SiC before alloying with silicon. The SiC buffer layer results in uniform alloying reactions between lithium and silicon on the surface around a silicon flake. RF carbon coatings provide enhanced electrical conductivity of SiC encapsulated silicon flakes. We characterized the coatings and anode by SEM, TEM, FTIR, XRD, cyclic voltammetry (CV), electrochemical impedance spectra (EIS), and electrical resistance measurements. Coin half-cells with combined SiC and RF carbon coatings exhibit an initial Coulombic efficiency (ICE) of 76% and retains a specific capacity of 955 mAh/g at 100th cycle and 850 mAh/g at 150th cycle of repetitive discharge and charge operation. Pre-lithiation of the anode increases the ICE to 97%. The SiC buffer layer reduces local stresses caused by non-uniform volume changes and improves the capacity retention and the cycling life.

Automated summary

The study focuses on using recycled silicon flakes coated with SiC and RF carbon coatings as active materials for LIB anodes. Thermal carbonization at 1000 degrees C forms 5-nm SiC encapsulating silicon flakes, providing physical strength and enhancing electrical conductivity. Experimental results show that coin half-cells with combined SiC and RF carbon coatings exhibit varying performance at different cycle numbers.