Effects of HF Acid on Dissolution of Elemental Si

Separating Si from mixture of Si and Si oxides using HF acid is an important prerequisite for preparing Si/C anode material for lithium ion battery. Increasing Si yield during the separation is desired. This requires understanding effects of HF acid on Si dissolution, but the effects were rarely studied. In this research, high-purity elemental Si was treated with HF acid under different conditions to investigate effects of HF concentration, treatment time, Si/solution ratio, and solvent composition on Si dissolution. The Si could be dissolved at room temperature at low HF concentration (2 wt%) within short contact period (& LE; 15 min), because of occurrence of reaction HF + Si & RARR; SiF4 & UARR; + H2 & UARR;. Dissolution of Si could be hindered by decreasing HF concentration or contact time, increasing Si/solution ratio, or adding ethanol into HF aqueous solution. Treating Si with HF-dissolved ethanol-water solution could promote formation of pores in Si. This research could provide guidance for high-yield recovery of Si and decreasing quantity of toxic fluorine during Si-SiOX separation.