Graphite@silicon embedded in a carbon conformally coated tiny SiO2 nanoparticle matrix for high-performance lithium-ion batteries

Abstract

Engineering of graphite@Si/carbon composites is considered as an effective strategy to surmount the shortcomings of the low conductivity and large volume expansion of bare Si anode materials for lithium-ion batteries. Nevertheless, their applications in high-performance electric vehicles are still challenging owing to their limited accessible capacity. Herein, SiO₂ as an active additive was introduced to improve the capacity of graphite@Si/carbon composites. Two different composites, graphite@Si sequentially embedded in SiO₂ and carbon layers (G@Si/SiO₂ layer/C) and encapsulated in a carbon conformally coated tiny SiO₂ nanoparticle matrix (G@Si/SiO₂ NPs/C), were well-designed. Both the Si/C composites exhibit a longer cycle life than the graphite@Si/C due to the unique double protective sheath of inert components (Li₂O and Li₄SiO₄) and carbon. The former was formed during the first lithium insertion of SiO₂. Specifically, the G@Si/SiO₂ NPs/C shows a high specific capacity (607 mA h g⁻¹), exceptional cycling stability (92% retention after 800 cycles at a 0.5 A g⁻¹) and promising rate capability. The remarkable performances benefit from the porous three-dimensional network structure constructed by an amorphous carbon matrix shell and a graphite core, which well disperse and support Si and SiO₂, thus improving their electrochemical activity, alleviating the volume change and increasing the Li-ion diffusion effectively.