Novel synthesis of porous Si-TiO2 composite as a high-capacity anode material for Li secondary batteries

Abstract

Porous Si materials can be considered as a candidate for and an alternative to commercial graphite anodes for Li-ion batteries. In this study, we propose a modified magnesiothermic method to increase the materials’ yield and a design strategy to improve their electrochemical properties. For magnesiothermic solid-state reactions, Mg2Si was used instead of metallic Mg and amorphous nanoscale SiO2 was adopted. The two starting materials were converted into Si and MgO via a high-temperature solid-state reaction, resulting in a high-yield percentage of Si. Then, amorphous TiO2 layers were formed and the MgO was removed by chemical etching, forming a porous structure. The materials at each step were thoroughly characterized by using various analytical tools. Electrochemical test results demonstrated that the amorphous TiO2 coated porous Si composite electrode exhibited a high reversible capacity of 1965 mA h g−1 after 100 cycles and a greatly improved initial Coulombic efficiency of 90.1%. These results can be attributed to the controlled porous structure of the composite and amorphous TiO2 coating layer. The modified magnesiothermic method and porous material design could attract commercial use of Si-based materials as Li-ion battery anodes.