Maximizing the utilization of active sites through the formation of native nanovoids of silicon oxycarbide as anode materials in lithium-ion batteries

Thus far, research on silicon oxycarbide (SiOC, SiOnC4-n (0 ≤ n ≤ 4)) as an anode material for lithium-ion batteries (LIBs) has been focused on the quantity and quality of the carbon domains. This study, however, intends to present a new perspective in order to maximize the utilization of active sites by forming nanovoids in the Si–O–C domain. Structural native nanovoids were formed by introducing PSS-Octakis (dimethylsilyloxy) silsesquioxane (POSS) into the synthesis process of SiOC, and it was then utilized as anode materials of LIBs. Moreover, the effects of POSS on the chemical, structural, and electrochemical properties of SiOC were investigated by varying the content of POSS. It was determined that the addition of POSS could form nanovoids, reduce the free carbon region, decrease the electrical conductivity, and increase the oxygen-rich tetrahedral Si–O–C structure. Despite the reduced electrical conductivity, the porosity formed by the addition of POSS induced high output characteristics by enabling fast ion diffusion to the active SiOC site during the repetitive lithiation/delithiation processes. Furthermore, the nanovoids were found to be capable of improving the structural stability during charge/discharge processes through a buffering effect. Moreover, the increased oxygen-rich tetrahedral Si–O–C structure was able to maximize reversible capacity. Such structural change resulted in a high specific capacity of 980 mAh g−1 at a current density of 180 mA g−1 as well as improved rate capability. A high specific capacity of 412 mAh g−1 was obtained even at a high current density of 3600 mA g−1, and 94% of the initial capacity was maintained after 200 cycles at a current density of 360 mA g−1.