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, SiO 2 , 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 ∼50 000 mAh/g‐atom, while “free carbon” can sequester ∼5000 mAh/g‐atom, for the reversible portion of the lithium insertion. The compositions lying close to the SiC–C, and SiC–SiO 2 tie lines, however, deviate measurably from this general picture.