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

Abstract

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 successfully prepared a-Si spheres (∼200 nm) by reducing the TiO2-coated silica spheres with Al powders in the molten salts at 300 °C. 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 cm2/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