Engineered Nanovoids in Si/C Composites for High Capacity and Stable Li-Ion Battery Anodes

Silicon is an ideal anode material for advanced Li-ion battery (LIB) because it offers a low voltage for charging and the highest specific and volumetric capacities (Li₁₅Si₄ » 3,579 mAh g^-1 and 8,340 mAh ml^-1) among known elements. In spite of these highly appealing features, it has long been a critical challenge to design silicon-based electrode materials in a scalable way which maintain their high capacity over prolonged cycling due to both disastrous electrode pulverization due to huge volume variations (~300%) and the instability of solid-electrolyte interface (SEI) layers. In this study, engineered carbon nanovoids were successfully introduced in the Si/C composites to efficeintly absorb the large volume expansions of silicon in the nanovoids and maintain electrical integrity of electrode as well as cycling stability for prolonged cycles. To explore the idea, chemical binding and electrostatic self-assembly between amine-functionalized Si nanoparticles and SiO₂ nanoparticles were employed followed by carbon coating and SiO₂ template removal. Thus prepared Si@Nanovoids delivered 1,350 mAh g^-1 at the current of 100 mA g^-1 and showed stable cycling up to 200 cycles at 500 mA g^-1 while the standard Si/C reference electrode lost most of its capacity in 40 cycles. The Si@Nanovoids electrode exhibited minimal volume change thanks to the engineered nanovoids after long cycles. More details in materials synthesis, analysis and electrochemical properties of Si@Nanovoids are to be presented.