Toward the Controlled Synthesis of Nanostructured Si and SiO x Anodes for Li-Ion Batteries via SiO2 Magnesiothermic Reduction Reaction

Nanostructured SiOx (0 <= x <= 2) materials are key for boosting energy density in next-generation Li-ion battery anodes, with the magnesiothermic reduction reaction (MgTR) emerging as a scalable pathway for their production from nanoporous SiO2. In MgTR, SiO2 reacts with Mg at moderate temperatures to form Si and MgO, enabling the preservation of nanostructured features. However, the widespread application of MgTR is hindered by the strong influence of reaction parameters on process dynamics, which leads to the uncontrolled formation of multiple byproducts that not only reduce the Si yield but also require the use of hazardous hydrofluoric acid (HF) for their removal, hampering the synthesis of SiOx due to HF's reactivity with SiO2. Hence, a comprehensive understanding of MgTR dynamics and its interplay with reaction parameters constitutes an essential prerequisite toward the effective synthesis of advanced Si and SiOx nanostructures. In this work, a systematic approach combining a set of independent time-resolved in situ synchrotron X-ray diffraction studies was employed to provide for the first time a comprehensive understanding of MgTR dynamics under varied reaction conditions, including varied SiO2 source (amorphous vs crystalline), different SiO2-to-Mg ratios, and different heating ramps. This approach allowed to unveil a complete picture of MgTR and to identify key conditions to prevent byproduct formation. This advancement marks a critical step toward the large-scale zero-carbon footprint synthesis of Si-based anodes for Li-ion batteries, serving as general guidelines for the controlled synthesis of high-purity Si and SiOx advanced materials.