Yolk-void-shell Si-C nano-particles with tunable void size for high-performance anode of lithium ion batteries

Silicon is a promising anode for new-generation lithium ion batteries due to high theoretical lithium storage capacity (4200 mAh g^-1). However, the low conductivity and large volumetric expansion hamper the commercialization of the silicon anode. In this case, we present a yolk-void-shell Si-C anode (denoted as Si@Void@C), which is synthesized through nano-Si oxidation, surface carbonization and etching of SiO _x . The void can be fabricated only by the self-generation and etching of SiO _x layer on the Si surface, without the help of template materials. Moreover, the void size can be adjusted only by means of the annealing temperature, which can be easily and precisely operated. The Si@Void@C/rGO with void size of 5 nm offers a discharge capacity of 1294 mAh g^-1 after 100 cycles at a current density of 500 mA g^-1. These enhanced performances can be ascribed to an appropriate size (5 nm) of void space which sufficiently accommodates the silicon volume expansion and stabilizes the carbon shell. At the same time, the voids effectively inhibit the growth of the solid electrolyte interface layer by depressing the decomposition of the electrolyte on the surface of Si in Si@Void@C/rGO. Furthermore, interfaces between Si@Void@C particles and rGO sheets construct bridges for electrons' conduction. In general, the present work provides a viable strategy for synthesizing silicon-carbon anode materials with long life.