Carbon-coated mesoporous silicon microsphere anodes with greatly reduced volume expansion

Carbon-coated nanostructured silicon (Si/C) composites are promising anodes for next-generation lithium-ion batteries, but scalable synthesis of such materials with an anti-pulverization capability, high areal capacity and long cycle life still remains a challenge. In this work, mesoporous Si/C microspheres of ∼165 nm diameter are synthesized by magnesiothermic reduction of porous silica followed by chemical vapor deposition of a thin carbon layer. They consist of numerous primary Si nanocrystals of ∼10 nm diameter which are interconnected, surrounded by abundant internal pores and coated with conductive graphitic carbon. These ameliorating structural and functional features offer a unique synergy that contributes to prevention of pulverization of Si/C microspheres with a highly reduced volume expansion of ∼85% upon full lithiation. The Si/C electrodes deliver a reversible capacity of ∼1500 mA h g^-1 at 0.1 A g^-1, an exceptional long-term stability of ∼90% capacity retention even after 1000 and 2500 cycles at 1.0 and 4.0 A g^-1, respectively, and an excellent areal capacity of ∼1.44 mA h cm^-2 after 500 cycles.