Lithium Insertion in Polymer-Derived Silicon Oxycarbide Ceramics

Data for the electrolytic insertion of lithium into polymer-derived silicon oxycarbide ceramics are analyzed in terms of a nanodomain model for these ceramics. The model is constructed from three molecular building blocks: graphene, silicon dioxide tetrahedra, and mixed bond tetrahedra. In mixed bonds, the silicon atom is shared by both oxygen and carbon. The composition regime being considered is bordered by a triangle formed by C, SiO2, and SiC. Mostly, the nonstoichiometric compositions containing free carbon are considered. The data fit a phenomenological description where silicon-based mixed bond tetrahedra sequester an equivalent of similar to 50 000 mAh/g-atom, while free carbon can sequester similar to 5000 mAh/g-atom, for the reversible portion of the lithium insertion. The compositions lying close to the SiC-C, and SiC-SiO2 tie lines, however, deviate measurably from this general picture.