Understanding the impact mechanism of the thermal effect on the porous silicon anode material preparation via magnesiothermic reduction
Abstract Magnesiothermic reduction of porous silica is a common method to prepare porous silicon anode materials. However, the influence of the thermal effect on the porous silicon material preparation has never been studied thoroughly. In this work, by adopting biosilica from the rice husks as the silica precursor, we study the impact mechanism of the thermal effect on the porous silicon material preparation deeply and comprehensively. It is found that the thermal effect during magnesiothermic reduction plays a very important role to maintain the nanostructure of the silica precursor. With the lower ramp rate of 1 degC min 1, less heat will accumulate and then the formation of the byproduct Mg2SiO4 as well as the agglomerative composite particles of Si and MgO with larger size can be avoided. The obtained product Si JRH 1 with the specific surface area of about 267 m2 g 1 and the pore volume of 1.1 m3 g 1 can basically maintain the interconnected nanoporous structure of the starting material of SiO2 JRH. It exhibits a reversible capacity of 1311 mA h g 1 after 100 cycles at a current density of 200 mA g 1 and 1177 mA h g 1 at 4 A g 1, much higher than those of commercial graphite anodes. The impact mechanism of the thermal effect can be applied to other magnesiothermic reduction to inherit the ideal nanostructure of the silica precursor.