Carbon-Free Conversion of SiO2 to Si via Ultra-Rapid Alloy Formation: Toward the Sustainable Fabrication of Nanoporous Si for Lithium-Ion Batteries

Silicon has the potentialto improve lithium-ion battery (LIB)performance substantially by replacing graphite as an anode. The sustainabilityof such a transformation, however, depends on the source of siliconand the nature of the manufacturing process. Today's siliconindustry still overwhelmingly depends on the energy-intensive, high-temperaturecarbothermal reduction of silica a process that adversely impactsthe environment. Rather than use conventional thermoreduction aloneto break Si-O bonds, we report the efficient conversion ofSiO(2) directly to Mg2Si by a microwave-inducedMg plasma within 2.5 min at merely 200 W under vacuum. The underlyingmechanism is proposed, wherein electrons with enhanced kinetics functionreadily as the reductant while the bombardment fromMg cations and electrons promotes the fast nucleation of Mg2Si. The 3D nanoporous (NP) Si is then fabricated by a facile thermaldealloying step. The resulting hierarchical NP Si anodes deliver stable,extended cycling with excellent rate capability in Li-ion half-cells,with capacities several times greater than graphite. The microwave-inducedmetal plasma (MIMP) concept can be applied just as efficiently tothe synthesis of Mg2Si from Si, and the chemistry shouldbe extendable to the reduction of multiple metal(loid) oxides viatheir respective Mg alloys.

Automated summary

Silicon has potential as a replacement for graphite in lithium-ion batteries to significantly improve performance, but the sustainability depends on the source and manufacturing process. Current silicon industry relies on energy-intensive, environmentally impactful methods. A new method utilizing microwave-induced magnesium plasma can directly convert SiO(2) to Mg2Si within minutes at low power, resulting in nanoporous silicon anodes that outperform graphite. This concept can also be extended to the synthesis of Mg2Si from Si and the reduction of other metal(loid) oxides using their respective magnesium alloys.