Mechanistic study of AlCl3 salt-enhanced reduction of SiO2

Abstract

Silicon-based materials have a variety of potentials to be employed, especially for the usage of anode material of Lithium-Ion-Battery (LIB) because of its superior electron capacity. Aluminothermic reduction, which refers to the reduction of SiO2 using Al metal and AlCl3 molten salt, has been proposed in literatures, but their suggestions were rather abstract to describe exact synthetic procedure. In this regard, the mechanism of the AlCl3 salt-enhanced Si reduction has been investigated with periodic monolayer kaolinite slab by density functional theory (DFT) calculation. For the initiation, atomic Al was detached from metallic Al surface with low activation energy while Al*-(AlCl3)2AlCl4 - complex was formed. Then, Si clustering took place via two competing reaction pathways, in which the reaction sequences were different to yield AlOCl. Comparison of reaction mechanisms in details revealed that the pre-adsorption mechanism, which refers that AlCl3 is separated from the complex first and Cl transfers to Al* center, was expected to be kinetically favorable. Finally, the formation of Cl2 gas was expected to maintain the activated state of Al at the center of the complex.