Simple and Safe Synthesis of Yolk-Shell-Structured Silicon/Carbon Composites with Enhanced Electrochemical Properties.

With its substantial theoretical capacity, silicon (Si) is a prospective anode material for high-energy-density lithium-ion batteries (LIBs). However, the challenges of a substantial volume expansion and inferior conductivity in Si-based anodes restrict the electrochemical stability. To address this, a yolk-shell-structured Si-carbon composite, featuring adjustable void sizes, was synthesized using tin (Sn) as a template. A uniform coating of tin oxide (SnO) on the surface of nano-Si particles was achieved through a simple annealing process. This approach enables the removal of the template with concentrated hydrochloric acid (HCl) instead of hydrofluoric acid (HF), thereby reducing toxicity and corrosiveness. The conductivity of Si@void@Carbon (Si@void@C) was further enhanced by using a high-conductivity carbon layer derived from pitch. By incorporating an internal void, this yolk-shell structure effectively enhanced the low Li/electron conductivity and accommodated the large volume change of Si. Si@void@C demonstrated an excellent electrochemical performance, retaining a discharge capacity of 735.3 mAh g after 100 cycles at 1.0 A g. Even at a high current density of 2.0 A g, Si@void@C still maintained a discharge capacity of 1238.5 mAh g.