Nanoporous silicon spheres preparation via a controllable magnesiothermic reduction as anode for Li-ion batteries

Magnesiothermic reduction is a facile and utility method for scalable synthesis of porous silicon. However, the severe heat accumulation during this process can lead to the porous structure collapse. In this work, we present an applied method for achieving a controllable magnesiothermic reduction through regulating the reaction rate by merely adjusting the particle size of magnesium. The impact effect of magnesium size on the reaction process is also systematically studied. It is found that the heat accumulation can be relieved when the size of magnesium is > 800 mu m (l-Mg). The obtained reduced silicon (l-rSi) can basically maintain the spherical shape and particle size of raw SiO2 and form a highly-developed nano-porous structure. It exhibits a high initial discharge capacity of 3191 m Ah g(-1) and coulombic efficiency of 80.9% with superior cycling stability and rate capability. Moreover, when the obtained l-rSi is added in commercial graphite with only 10 wt%, the capacity of l-rSi/commercial graphite composite increases to 670 m Ah g(-1), which is about 2 times that of commercial graphite, manifesting great potential for industrial application. Our work can be a guide to fabricate nanostructure silicon materials through magnesiothermic reductions for the silicon-based anode of lithium-ion batteries. (C) 2019 Elsevier Ltd. All rights reserved