Low-Cost Silicon\nfrom Natural Sand with Tunable Oxygen\nContent and Its Effects on the Electrochemical Properties of Lithium-Ion\nBattery Anodes

Silicon (Si) is recognized as a promising anode material\nfor lithium-ion\nbatteries (LIBs). However, the significant volume expansion during\nlithiation poses a make-or-break challenge for the commercial adoption\nof silicon as an anode. The solutions to mitigate the challenge often\ndepend on processes that can increase costs for the LIB. Here, we\ndemonstrate a magnesiothermic reduction process that uses low-cost\nnatural sand as the raw material to produce battery-grade silicon\nwith a high conversion rate of ∼98%. The magnesiothermic reduction\nprocess can produce Si products with varying oxygen content depending\non certain process parameters, including the Mg:Si molar ratios and\ntemperature. Therefore, we also investigated the effect of the oxygen\ncontent on electrochemical performance as an anode. The results show\nthat the initial discharge capacity and initial Coulombic efficiency\n(ICE) decrease linearly with increasing oxygen content. In contrast,\nthe capacity retention and the lithium-ion diffusion coefficient (<i>D</i><sub>Li</sub>) exhibited an opposite trend. By comparing\nthe electrochemical impedance spectroscopy and <i>D</i><sub>Li</sub> of those samples, we observed that samples with a high-oxygen\ncontent showed smaller change in charge transfer impedance after cycling\nwhile their <i>D</i><sub>Li</sub> increased.