Alumina coated nano silicon synthesized by aluminothermic reduction as anodes for lithium ion batteries

Alumina (Al2O3) coated nano silicon was synthesized by aluminothermic reduction for the first time. It was realized by preoxidation of the nano silicon followed by a aluminothermic reduction that transformed the surface silicon oxide into Al2O3. The thickness of Al2O3 can be controlled by regulating the preoxidized temperature and the processing time. The nano silicon coated with 2-4 nm Al2O3 showed a more stable cycling performance and a higher coulombic efficiency than the uncoated nano silicon. It is believed that the improved electrochemical performance was benefited from the Al2O3 coating, which could hinder the side chemical reactions during the cycling process. This work provides an alternative method for surface coating on nanomaterials by safe and flexible solid state chemical reaction.