Magnesium vapor-phase-driven synthesis of morphology-preserved silicon nanoparticles from silica for lithium-ion batteries

Abstract

Silicon nanoparticles offer an exceptional theoretical capacity for lithium-ion battery anodes, yet their scalable synthesis from abundant precursors remains hindered by costly and complex processes. Magnesiothermic reduction (MTR) of silica offers a cost-effective alternative using non-toxic precursors, but under atmospheric pressure, it often leads to severe particle aggregation and byproduct formation due to heterogeneous reactions with molten magnesium. Here, we demonstrate that low-pressure conditions (∼1 Torr) fundamentally alter the MTR mechanism by facilitating uniform vapor-phase magnesium transport, thereby enabling the synthesis of silicon nanoparticles. The resulting nanoparticles deliver 2166 mA h g−1 capacity with 73.6 % capacity retention after 100 cycles, substantially outperforming silicon synthesized under atmospheric pressure MTR (33 % retention). Unlike previous MTR studies that consistently yield micrometer-scale aggregated particles regardless of precursor size, our pressure-controlled method enables the synthesis of silicon nanoparticles. This work establishes fundamental design principles for pressure-controlled metallothermic processes that achieve thermal management without a heat-sink medium and demonstrates gram-scale synthesis of high-performance silicon anode materials.