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

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 degrees C using methyltrichlo rosilane (CH3SiCl3) 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 degrees 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.