A low temperature MgH2-AlCl3-SiO2 system to synthesize nano-silicon for high-performance Li-ion batteries

Abstract Nano-silicon is a star anode material for the next generation Li-ion batteries with the merits of high theoretical capacity and low voltage plateau. To date, it remains a great challenge to efficiently convert low-cost silica (SiO2) into nano-Si at a low temperature due to the solid Si-O band (the bond energy is 460 kJ mol−1). Herein, a low temperature MgH2-AlCl3-SiO2 melt system is developed to synthesize nano-Si through the reduction of SiO2 by MgH2 in the molten AlCl3. It is confirmed to be a controllable liquid-solid process with no side reactions and high Si yield of 97.6%. The battery grade nano-Si product can be obtained by suitable post-treatment without undesirable HF etching. This reaction can be initiated at as low as 150 °C, which is much lower than mostly reported synthesis routes of nano-Si. The nano-Si product with an average particle size of 22.4 nm exhibits superior electrochemical storage capacity of 1185 mA h g−1 over 300 cycles at 0.2 A g−1 and a low increased thickness of 14.5% at 2 A g−1 over 500 cycles. We believe that this low temperature melt system not only paves the new path of synthesizing nano-Si, but also gives a new insight into the effects of nanoscale particle size on the electrochemical performance of Si anode.