SURFACE DECORATION OF COMMERCIAL GRAPHITE MICROSPHERES WITH SMALL Si/C MICROSPHERES AS IMPROVED ANODE MATERIALS FOR Li-ION BATTERIES

Abstract

We report a facile chemical vapor deposition (CVD) method to grow silicon/carbon ( Si / C ) microspheres on commercial graphite microsphere (GMs) surface to prepare Si / C / GMs composite anode materials for Li -ion batteries. The CVD synthesis is conducted at 900°C using methyltrichlorosilane ( CH 3 SiCl 3) as both the Si and C precursor, which is a cheap byproduct in organosilane industry. The samples are characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy and X-ray photoelectron spectroscopy. It is found that the obtained Si / C / GMs composites are composed of Si nanocrystals, amorphous carbon and GMs. The CVD time significantly influences the morphology and electrochemical performance of the Si / C / GMs composite materials. The Si / C / GMs composite materials prepared at CVD condition of 900°C for 4 h possess improved electrochemical properties, showing a discharge capacity of 821.4 mAh g−1 at a rate of 50 mA g−1, and a good cycling performance (i.e., a reversible capacity of 565.2 mAh g−1 is retained after 50 cycles). The enhanced electrochemical performance is attributed to the formation of Si / C microsphere network among GMs, which increases the electronic conductivity and is able to buffer the large volume changes of Si during lithium ion insertion/extraction.