Ball-Milling-Assisted Magnesiothermic Reduction of Clay Minerals to Nano-Si as High-Performance Lithium-Ion Battery Anodes

Nanosilicon (Si) holds exceptional promise for next-generation high-energy-density lithium-ion batteries, yet its practical application is hindered by costly and complex synthesis. Here, we present a universal and scalable strategy to synthesize porous nano-Si from natural clay minerals via ball-milling-assisted magnesiothermic reduction, without pretreating clay or external heating. The self-heating ball-milling process enhances energy efficiency while enabling uniform reactions. The inherent aluminum-oxygen octahedral layers in montmorillonite inhibit Si nanocrystal aggregation and buffer temperature by self-decomposition. Moreover, only 0.4 equiv of NaCl relative to the precursor are sufficient to suppress high-temperature byproduct formation, while simultaneously promoting the fragmentation of montmorillonite layers to accelerate the reaction. The obtained nano-Si features a small crystalline size (∼26 nm), hierarchical porosity, and a moderate specific surface area. After carbon-encapsulating and blending with graphite, the Si@C/G composite delivers 699 mAh g^-1 with a high initial Coulombic efficiency of 87.1%, and retains 90.0% capacity over 200 cycles.