Electrochemical Performance of Polymer-Derived Silicon-Oxycarbide/Graphene Nanoplatelet Composites for High-Performance Li-Ion Batteries

Amorphous polymer-derived silicon-oxycarbide (SiOC) ceramics have a high theoretical capacity and good structural stability, making them suitable anode materials for lithium-ion batteries. However, SiOC has low electronic conductivity, poor transport properties, low initial Couloumbic efficiency, and limited rate capability. Therefore, there is an urgent need to explore an efficient SiOC-based anode material that could mitigate the abovementioned limitations. In this study, we synthesized carbon-rich SiOC (SiOC-I) and silicon-rich SiOC (SiOC-II) and evaluated their elemental and structural characteristics using a broad spectrum of characterization techniques. Li-ion cells were fabricated for the first time by pairing a buckypaper composed of carbon nanotubes with SiOC-I or SiOC-II as the anode. When mixed with graphene nanoplatelets, the SiOC-II/GNP composites exhibited improved electrochemical performance. High specific capacity (average specific capacity of 744 mAh/g at a 0.1C rate) was achieved with the composite anode (25 wt % SiOC-II and 75% GNP), which was much better than that of monolithic SiOC-I, SiOC-II, or GNPs. This composite also exhibited excellent cycling stability, achieving 344 mAh/g after 260 cycles at a 0.5C rate and high reversibility. The enhanced electrochemical performance is attributed to better electronic conductivity, lower charge-transfer resistance, and short ion diffusion length. Due to their superior electrochemical performance, SiOC/GNP composites with CNT buckypaper as a current collector can be considered a promising anode material for LiBs.