Si-O network encapsulated graphite-silicon mixtures as negative electrodes for lithium-ion batteries

Graphite-silicon mixtures are encapsulated in a Si-O network derived from sol-gel transformation of alkoxy-silane(methyl-trimethoxy-silane). The composites are characterized by powder X-ray diffraction and scanning electron microscopy. The catalyst used in the sol-gel process significantly affects the electrochemical properties of the composites. The initial specific capacity of the composites is close to 500 mA h g(-1) which is between that of graphite alone (similar to 300 mA h g(-1)) and mechanical mixtures of graphite and silicon of identical silicon contents (similar to 900 mA h g(-1)). Base (NH4OH) catalyzed composites perform substantially better than acid (HCl) catalyzed composites. The experimental results have yet to demonstrate any real advantage of the composites over graphite in terms of cycleability. Nevertheless, this approach should not be dismissed as the network material in this study may not have been optimized. (C) 2001 Elsevier Science B.V. All rights reserved.