Preparation of Hollow Nanostructured Si Spheres by Zincothermic Reduction of SiO2 to Si for Lithium-Ion Batteries

The choice of SiO2 precursor plays an important role in designing and synthesizing specific nanostructured Si materials with improved Li-storage performance. Herein, various SiO2 precursors are used to prepare nanostructured Si spheres via zincothermic reduction and their effects on the reduction process are systematically investigated. It is found that the size and structure of SiO2 precursors have a significant effect on the zincothermic reduction process. Among various precursors, nano-SiO2 and bio-SiO2 (e.g., SiO2 derived from rice husk (RH-SiO2) and bamboo leaves (BL-SiO2)) are successfully reduced to Si spheres, while crystalline bulk SiO2 (i.e., micro-SiO2) cannot be reduced. The ease of zincothermic reduction of nano- and bio-SiO2 is due to the high surface area of SiO2 that allows sufficient and facile chlorination–reduction reactions. In addition, the hollow Si spheres prepared from nano-SiO2, RH-SiO2, and BL-SiO2 are used as anode materials for lithium-ion batteries, all of which exhibit good electrochemical performances, delivering the specific discharge capacities of 947.6, 1130.7, and 1050 mAh g–1 over 300 cycles at 1 A g–1, respectively. Overall, this work offers a deeper understanding of zincothermic reduction and demonstrates the broad applicability of zincothermic reduction for the preparation of nanostructured Si from a variety of Si sources.