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, we 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 similar to 300 mAh g(-1), in the absence of silicon, to near 500 mAh g(-1) as silicon is added. For silicon content <6 atomic percent, the reversible capacity increases linearly with a slope of approximately 30 mAh g(-1) per percentage point silicon. This suggests that each silicon atom can reversibly bond with similar to 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. It is our view that 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.