Synthesis and electrochemical performance of Si/natural graphite/pitch carbon composites as the anode of a lithium ion battery

Composites with a pitch-based carbon (PC) matrix and a mixture of nanoparticle silicon and natural flake graphite (NG) as filler (Si-NG/PC) was prepared by high energy mechanical milling of mixtures of nano-Si, NG and high softening point pitch, followed by pyrolysis at 1000℃ for 2h to convert the pitch into carbon. The influence of the preparation conditions on the electrochemical properties of the composites for use as the anode of a lithium ion battery was investigated. This included milling time, rotation speed and the precursor formulations. XRD and SEM were used to examine the composition and structure of the composites. Results indicated that the optimum milling time is 21h at a rotation speed of 300r/min, and the optimum proportions of nano-Si and pitch carbon in the composites were less than 35wt.% and around 30wt.%, respectively. Under the optimized conditions, the Si-NG/PC composite presented a high specific capacity and a good cycling stability when tested for 50 cycles.