Amorphous silicon from low-temperature reduction of silica in the molten salts and its lithium-storage performance

Amorphous silicon(a-Si) is one of the most promising anode-materials for the lithium-ion battery owing to its large capacity and superior fracture resistance.However,a-Si is usually fabricated with the sophisticated chemical vapor deposition or pulse laser deposition in a limited scale.In this work,we have succes s fully pre pared a-Si spheres(~200 nm) by reducing the TiO2-coated silica spheres with Al powders in the molten salts at 300℃.The coated TiO2 layer acts as a protective layer for structural maintenance during the reduction and a precursor for doping.The doped Ti element may suppress the crystal growth of Si to facilitate the formation of a-Si.The observation with in-situ transmission electron microscopy(TEM) further reveals that lithiation kinetics of the synthesized a-Si is controlled by the interfacial reaction.The Li^(+) diffusivity in a-Si determined from the observation is in the order of 10^(-14) cm^(2)/s.The anode of a-Si spheres together with crystalline Si nanoparticles exhibits excellent electrochemical performance,delivering a reversible capacity of 1604 mAh/g at 4 A/g and a capacity retention of 78,3%after 500 cycles.The low temperature reduction process reported in this study provides a low-cost method to fabricate a-Si nanostructures as high-capacity durable anode materials.