Multi-step low-cost synthesis of ultrafine silicon porous structures for high-reversible lithium-ion battery anodes

We demonstrate multi-step synthesis of silicon porous structures with various particle sizes via low-cost annealing and pickling reactions from ball-milled Mg₂Si or Si/Mg powder. Thereinto, the ultrafine Si porous structures (< 50 nm) have been prepared by the two-step alloying/de-alloying processes between Si and Mg, and the formation processes and reaction mechanism have been discussed as well. When used as an anode material for lithium-ion batteries, the porous Si anode with finer particle size shows better capacity retention and coulombic efficiency, confirming the particle size has a great impact on cycling performance. Moreover, the ultrafine porous Si anodes without any buffer medium demonstrate a reversible discharge capacity of ~ 800 mAhg⁻¹ after 1000 long cycles at 1 Ag⁻¹, which is extremely better than the commercial nano-Si particles and graphite anodes. It is believed that the good electrochemical performance could be attributed to the uniform porous structure and superfine particle size that can alleviate the volume change significantly. Hence, these low-cost and simple scalable methods have provided useful strategies for the industrialization of Si anode materials.