Electrochemical Performance of Silicon/Carbon/Graphite Composite Anode for Lithium Ion Batteries

Silicon and graphite with polyvinylidene fluoride as the matrix was pyrolyzed to obtain the Si/C/graphite composite anode with the stable and excellent electrochemical performance. The morphology of the composite was characterized by transmission electron microscope (TEM). The result showed that the composite had core-shell structure in which silicon particles were wrapped by the amorphous carbon. The effects of the silicon particle size and the graphite content on the electrode electrochemical performance were investigated systematically. It reveals that the fine size of silicon particles is beneficial to obtain a stable electrochemical performance. The appropriate content ratio of graphite and silicon is necessary to increase the reversible capacity of the composite. When the mass ratio of silicon to graphite is 1:1 and the silicon particle size is 50 mu, the Si/C/graphite composite presents the first discharge specific capacity of about 1741.6 mAh/g and the first coulombic efficiency of 72.4%. The reversible specific capacity still remains 820 mAh/g after 60 cycles. It demonstrates that the carbon-coating structure can be obtained by pyrolyzing the organic matter which will improve the electrochemical performance of the silicon-based anodes effectively.