Carbon-Doped Silicon Nanoparticles in Thermally Reduced Graphene Oxide Composites for High-Capacity Lithium-Ion Battery Anodes

Abstract

Silicon is a promising anode material for next-generation lithium-ion batteries due to its high theoretical capacity (3600 mAh/g), natural abundance, and low cost. However, its practical application is limited by severe ~300% volume expansion during lithiation, leading to rapid capacity fading and poor cycling stability. In this work, recent literature on silicon anodes is reviewed and compared using a novel framework, highlighting the challenge of achieving stable cycling at high areal loadings. Building on these insights, carbon-doped silicon nanoparticles, which are known for their ability to mitigate lithiation-induced stress, are investigated in thermally reduced, spray-dried core-shell composites with reduced graphene oxide (rGO). The thermal reduction temperature of rGO is also varied to assess its impact on electrochemical performance. When encapsulation by rGO was effective, the carbon-doped silicon nanoparticles enhanced both rate performance and cycling stability of the core-shell silicon-rGO composites (Si@rGO), compared to undoped silicon. Among the tested reduction temperatures, 950 °C yielded the best rate performance, balancing rGO deoxygenation (which improves conductivity) with the formation of inactive silicon carbide at higher temperatures (which lowers specific capacity). The optimized Si@rGO composite, featuring carbon-doped silicon and reduced at 950 °C, delivered a specific capacity of 957 ± 53 mAh/g with 74.8 ± 2.4% capacity retention after 160 cycles. Finally, the energy density of a theoretical full battery pairing with NMC881 was estimated, projecting an 18% increase in energy density over a conventional graphite–NMC881 cell at commercial mass loadings.