Deciphering fast lithium storage kinetics via R-based self-derivation effects in siloxanes

Silicon oxycarbide (SiOC) is regarded as a promising anode material for lithium-ion batteries. However, the effect of SiOC's structural composition on lithium-ion storage behaviors, especially the controllable introduction of free carbon (Cfree) and its influence on electrochemical performance, remains a critical challenge that needs to be solved. In this study, based on our finding that the R-based functional group (composed exclusively of carbon and hydrogen atoms) in R-based triethoxysilane can be derived to carbon radicals through thermal decomposition, and then generates Cfree phases into SiOC, we propose a novel concept of R-based self-derivation effects in siloxanes to achieve controlled Cfree introduction for the SiOC anode material. SiOC spheres with tailored structural compositions and Cfree contents are subsequently prepared using a facile and scalable polymeric precursor method, and the effect of Cfree of SiOC spheres on lithium-ion storage performance is studied in combination with density functional theory calculations, revealing that higher Cfree content significantly enhances the lithium-ion storage kinetics of SiOC anode via constructing ion/electron migration "highways". Notably, SiOC with a high Cfree content up to 37.5 wt% displays excellent lithium-ion storage capability, with a theoretical storage capacity of up to 1004 mAh g−1 and achieving a high reversible capacity of 453 mAh g−1 after 200 cycles at 0.5 A g−1.