Thermo-Kinetic Design of Magnesiothermic Reduction for Morphology-Retaining Porous Si@C Anodes

Silicon (Si) is a promising anode material for replacing graphite, but nano-sized Si suffers from low electrode density, whereas micro-sized Si undergoes severe volume expansion and structural degradation, limiting cell-level performance. Magnesiothermic reduction, a conventional route for converting silica precursors into Si, often causes impurity formation and morphology collapse because Mg supply is not balanced with the surface reaction rate. A thermo-kinetic process model is introduced to guide process design by balancing Mg supply and surface consumption during reduction. By tuning reaction conditions to maintain this balance, Stöber SiO₂ is converted into monodisperse spherical porous Si without aggregation. A carbon exoskeleton is introduced before acid etching to preserve the fragile porous framework during purification. Under the optimized condition, the resulting Si@C delivers a reversible capacity of 1571.1 mAh g^-1 at the 100th cycle with an initial coulombic efficiency of 74.2%. The porous architecture and carbon exoskeleton mitigate mechanical degradation, while the monodisperse spherical morphology promotes more uniform electronic and ionic transport and reaction distribution within the electrode. These results demonstrate an effective process platform for producing morphology-retaining porous Si@C through integrated thermo-kinetic control and carbon-assisted stabilization.