Low-Cost Silicon from Natural Sand with Tunable Oxygen Content and Its Effects on the Electrochemical Properties of Lithium-Ion Battery Anodes.

Silicon (Si) is recognized as a promising anode material for lithium-ion batteries (LIBs). However, the significant volume expansion during lithiation poses a make-or-break challenge for the commercial adoption of silicon as an anode. The solutions to mitigate the challenge often depend on processes that can increase costs for the LIB. Here, we demonstrate a magnesiothermic reduction process that uses low-cost natural sand as the raw material to produce battery-grade silicon with a high conversion rate of ∼98%. The magnesiothermic reduction process can produce Si products with varying oxygen content depending on certain process parameters, including the Mg:Si molar ratios and temperature. Therefore, we also investigated the effect of the oxygen content on electrochemical performance as an anode. The results show that the initial discharge capacity and initial Coulombic efficiency (ICE) decrease linearly with increasing oxygen content. In contrast, the capacity retention and the lithium-ion diffusion coefficient ( ) exhibited an opposite trend. By comparing the electrochemical impedance spectroscopy and of those samples, we observed that samples with a high-oxygen content showed smaller change in charge transfer impedance after cycling while their increased.