Temperature-Dependent Formation of Carbon Nanodomains in Silicon Oxycarbide Glass─A Reactive Force Field MD Study

Novel anode materials for lithium-ion batteries (LIBs) are constantly being explored to further improve battery performance. In this work, ReaxFF molecular dynamics (MD) simulations are performed to model the early stages in the synthesis of nanostructured silicon carbide (SiC), which is one such promising material. The focus lies on its precursor, silicon oxycarbide glass of composition (Si₅O₈C₁₆)_x (17 mol% Si, 28 mol% O, and 54 mol% C), in the following referred to as SiOC. The structure of the amorphous material is characterized via NPT MD simulations at temperatures ranging from 300 to 1000 K. To this end, a graph theoretical approach is employed to quantify the formation of segregated carbon nanodomains in the solid. Three algorithms for detecting nearest neighbors in the amorphous solid, a crucial prerequisite for the assembly of an atomic connectivity graph, are compared. It is shown that the temperature-dependent carbon aggregation follows an exponential trend, largely independent of the neighbor detection method. Also, the effects of variations in elemental composition are explored. Furthermore, the calculated powder X-ray diffraction patterns of the equilibrated silicon oxycarbide glasses are in good agreement with experimental measurements.