Chemical reduction of SiCl4 for the preparation of silicon-graphite composites used as negative electrodes in lithium-ion batteries

Silicon-graphite composites were prepared by direct reduction of liquid SiCl4 by various alkali metal graphite-intercalation compounds (GICs). The reaction occurred in all cases and led to intimate mixtures of nanosized silicon and graphite. A cleaning procedure has been used to solubilize the alkali chlorides formed as by-products. Even if silicon is hardly detected when the synthesis is performed from KC8, the experiments conducted with LiC6 lead to nanocrystallized silicon particles well dispersed in the graphite matrix. The Si-graphite composite (9: 91 by weight) issued from LiC6 displays a first-charge capacity of 610 mAh/g, which is in fairly good agreement with the theoretical expected value (656 mAh/g), assuming the formation of the Li3.75Si phase. Interestingly, this Si-C composite exhibits a better capacity retention than similar Si-C composites prepared by ballmilling; the charge capacity is still above 500 mAh/g after 10 cycles. This suggests the existence of a strong interaction between carbon and Si nanoparticles, which may be explained by the formation and growth of silicon when in contact with the graphene sheets. These preliminary electrochemical results point out the use of such an approach of chemical reaction between GICs and SiCl4 for the preparation of Si-C composites. (c) 2008 The Electrochemical Society.