Synthesis and performance of nanostructured silicon/graphite composites with a thin carbon shell and engineered voids

Utilizing silicon as an anode material for Li-ion batteries has been the subject of many studies. However, due to the huge volume change of silicon during lithiation, the electrochemical performance of silicon is poor. Here, we have investigated a novel yet simple approach to synthesize nanostructured silicon/graphite composites with a carbon coating and engineered voids. High-energy ball mill is employed to convert micrometer-sized silicon and graphite to nanostructured silicon/graphite composite building blocks, while a thin carbon coating is applied to encapsulate these composite agglomerates, followed by partial etching of silicon to create engineered voids inside the composite agglomerates. The batteries made with this tailored nanostructure exhibit improved electrochemical performance over the counterparts made with silicon nanoparticles and exhibited a specific capacity of ∼1800 mA h g−1 discharge capacity at the first cycle, 580 mA h g−1 after 40 cycles, and 350 mA h g−1 after 300 cycles. This study has established a novel method scalable at industry environment and capable of producing low cost Si anodes and clearly shown that the cycle stability of the tailored nanostructure improves with increasing engineered voids in the range we have investigated.