The effect of carbon coating on graphite@nano-Si composite as anode materials for Li-ion batteries

The graphite@nano-Si@C composite was prepared by a designed hot reactor with stirring function by coating pitch carbon on the surface of graphite@nano-Si composite, and the effect of the carbon coating on the structure and electrochemical properties of the composite was also investigated by physical characterization and electrochemical measurement technologies. The pitch carbon coating can decrease the surface area of graphite@nano-Si@C composite, and there are no silicon nanopowders bared on the surface. The first discharge/charge capacity of graphite@nano-Si composite is 644.6 and 582.1 mAh g with initial coulombic efficiency of 90.31%, and the capacity retention after 300 cycles is 66.03%. The pitch carbon coating layer impedes delithiation reaction leading to the increase of delithiation voltage, which also affects the charge transport ability of graphite@nano-Si@C composite before activation. However, the capacity retention of graphite@nano-Si@C composite corresponding to 10 wt% and 20 wt% pitch addition after 300 cycles reaches 80.90% and 84.51% with first discharge capacity of 623.6 and 618.8 mAh g, respectively, which is attributed to the pitch carbon coating layer can stable the SEI film and buffer volume expansion to enhance the cycle performance.