Synthesis and Electrochemical Properties of CNFs-Si Composites as an Anode Material for Li Secondary Batteries

We have performed a study on the electrochemical and structural characteristics of CNFs-Si composites which are active anode material for lithium secondary batteries. Carbon nanofibers (CNFs) have been synthesized by Chemical Vapor Deposition (CVD) using Co and Cu catalysts. The CNFs on the surface of the Si particle can provide a flexible space to relieve the volumetric expansion during a charge. Therefore, the CNFs composites on Si particles were prepared on the basis of the following two processes: (1) CNFs were grown on the simple mechanical mixture of Si particles and catalysts (CNFs/Si); (2) CNFs were grown on the surface of a pyrolytic carbon that was coated with Si particles (CNFs/PC/Si). The morphology and composition of CNFs-Si composites were analyzed by SEM and EDS measurements. Crystallinity and amorphicity were investigated using XRD and Raman spectroscopy. The characteristics of the synthesized CNFs-Si composites were analyzed through XPS, TGA, and BET. The two different CNFs-Si composite materials were evaluated as the anodic material in three different electrode cells. We found that the initial capacity of the CNFs/PC/Si composite electrode was 1,361 mAh/g with retention rate of 28.4%, which was better than the retention rate of 4.9% with the CNFs/Si electrode.