Lithium Insertion in Carbons Containing Nanodispersed Silicon

Graphite and pregraphitic carbons are intercalation hosts commonly used in Li ion cells. Using chemical vapor deposition of benzene and of silicon-containing precursors, the authors have prepared carbons containing nanodispersed silicon. The silicon resides within the unorganized regions in the pregraphitic carbons. Materials with up to 11% atomic silicon have been prepared. These materials reversibly react with lithium in electrochemical cells and the reversible specific capacity increases from {approximately}300 mAh/g, in the absence of silicon, to near 500 mAh/g as silicon is added. For silicon content < 6 atomic percent, the reversible capacity increases linearly with a slope of approximately 30 mAh/g per percentage point silicon. This suggests that each silicon atom can reversibly bond with {approximately}1.5 lithium atoms. The increased capacity due to the silicon appears as a broad feature in the differential capacity between 0.1 and 0.6 V vs. Li metal. The large reversible capacities are maintained over many charge/discharge cycles. The carbonaceous matrix provides a pathway for diffusion of Li to the nanodispersed silicon atoms, while it can still intercalate a substantial amount of lithium. Nanodispersions of other lithium alloying atoms in carbon probably can be prepared.