Aluminum as a bi-functional reducing agent for the fabrication of graphene encapsulated silicon microspheres as anodes for high-performance lithium-ion batteries

The composites of reduced graphene oxide (rGO) encapsulated porous silicon (P-Si) microspheres are constructed using metallic aluminum as a bi-functional reducing agent at low temperatures. The preparation process of P-Si is carried out in a special reactor at 300 °C. For the reaction, SiO2 is used as the silicon source and AlCl3 is added to maintain the smooth progress of the thermite reduction reaction. Subsequently, graphene oxide is reduced by aluminum powder in an acidic liquid phase system and then the P-Si/rGO composite material is constructed by freeze-drying technique. As a kind of promising anode for lithium-ion batteries (LIBs), the porous structure of silicon microspheres can relieve the internal stress caused by volume expansion and shorten the diffusion path of lithium ions during charge/discharge processses. The flexible graphene layers can adapt the volume effect of the P-Si microspheres and therefore maintain the structural stability of the composites and enhance the electrical conductivity. The obtained P-Si/rGO composite material exhibits excellent electrochemical performance, which can maintain a superior capacity of 837 mAh g−1 upon 500 cycles under a current density of 0.5 A g−1 and exhibit satisfied cycling stability with a capacity of 704 mAh g−1 after 1000 cycles at a 1 A g−1 current density.