Low-Cost Clean One-Step Production of Solar Silicon from Natural Quartzite

Abstract

Despite the fact that many groups have tried to achieve solar silicon production using molten salt electrolysis, the motivation for this project is to build on a recent breakthrough in silicon molten salt chemistry. The novel molten salt bath comprised of MgF₂-CaF₂-YF₃-CaO-SiO₂ exhibits low volatility (<0.1 μg/cm2·s), low viscosity (<5 mPa·s), high ionic conductivity (>4 S/cm), SiO₂ solubility (>5 wt%), and yttria-stabilized zirconia (YSZ) solid oxide membrane (SOM) compatibility, which are all at least an order of magnitude better than prior works. Our goal is to produce high-purity silicon from natural 99.7-99.9% pure quartzite (SiO₂) in only one step, utilizing molten salt electrolysis with a state-of-the-art molten salt composition. This process can potentially produce silicon with 4-5N purity at $1.70/kg using <30 kWh/kg, with pure oxygen by-product and zero direct Greenhouse Gas (GHG) emissions. The 4-5N product purity would be sufficient for directional solidification, resulting in $2.20-2.70/kg solar-grade silicon cost, i.e., 90-95% lower than today. Besides considerable silicon price reduction, our novel technology provides a high level of scalability that can control solar silicon price fluctuations, while it is a "green" production.