Surface treatment of silicon coated synthetic flake graphite as a negative electrode of lithium secondary batteries

Commercial rechargeable lithium batteries are employed as power supplies for cellular phones and portable computers. Usually carbonaceous materials have been used as the negative electrode because of their better cycling performance and dimensional stability compared to lithium alloys. To increase the specific capacity of the lithium secondary batteries, silicon is considered as one of the promising alternative anode materials. According to the electrochemical reactions between silicon and lithium, silicon can alloy with lithium up to 4.4 Lithium/silicon at high temperature. Theoretical capacity of silicon is ∼ 4000 mAh/g. However, silicon is difficult to apply due to poor cyclability caused by severe volume expansion and due to high irreversible capacity at first cycle. For the carbon-silicon composite system, synergy effect of silicon-carbon composite system is expected. In this system, silicon acts as lithium alloying reactants during charge-discharge process and also carbon matrix play a role as the lithium intercalation sites and conducting medium between silicon particles as well. The relationship between electrochemical properties of silicon coated graphite and the heat treatment condition in hydrogen atmosphere is presented. This is an abstract of a paper presented at the 229th ACS National Meeting (San Diego, CA 3/13-17/2005).