Impact of the electrical conductivity on the lithium capacity of polymer-derived silicon oxycarbide (SiOC) ceramics

Abstract

Within this work, we systematically investigate the influence of the amount of free carbon phase on the electrical conductivity and the lithium storage capability of silicon oxycarbide (SiOC) materials. A series of SiOC ceramics comprised of free carbon content ranging from 8 to 54wt.% is examined. The ability to reversibly host lithium ions is correlated with the elemental composition and the electrical conductivity. The materials with low carbon content up to ∼20wt.% reveal conductivities lower than 310−5Sm−1 and initially high capacities of more than 1000mAhg−1, which fade rapidly with continuous cycling. For the samples with higher amounts of free carbon phase, higher electrical conductivities ranging from 0.07 to 2.2Sm−1 are measured. In comparison to the carbon-poor materials, the carbon-rich samples demonstrate enhanced accessibility of Li-ion storing sites with capacities of more than 500mAhg−1. Moreover, a linear dependence between a stable capacity after 60 cycles and free carbon content in the ceramic is found.