Low-Cost Silicon from Natural Sand for Lithium-Ion Batteries and Its Electrochemical Response to Oxygen Content

The cost-effectiveness is an essential factor to be considered for the commercial viability of Silicon (Si) anode for lithium-ion batteries, alongside factors such as electrochemical performance and safety considerations. Here, we utilized low-cost natural sand as raw material and employed the magnesiothermic reduction method to produce battery-grade silicon with an impressive ~98% yield rate. Additionally, Si with varying oxygen content was produced by adjusting the stoichiometry of magnesium and reduction temperature. We also explored the effect of oxygen content on the electrochemical performance as an anode. Our findings indicated a linear decrease in both the initial discharge capacity and initial coulombic efficiency with increasing oxygen content. In contrast, the capacity retention at the 20^th cycle and the lithium-ion diffusion coefficient exhibited an opposing trend. By comparing the electrochemical impedance spectroscopy and lithium-ion diffusion coefficient of those samples, we observed that the sample with high-oxygen content samples displayed less change in charge transfer impedance after cycling, while their lithium-ion diffusion coefficient exhibited a more pronounced increase.