Reduction kinetics of porous silicon synthesis for lithium battery anodes

Abstract

Porous silicon (pSi) microparticles can be favorably employed as the high-capacity and stable anode materials in all formats of lithium-based batteries. Magnesiothermic reduction reaction (MRR) of low-cost silica produces pSi structures at relatively low temperatures; however, yield and reduction selectivity are currently limited. Herein, we conduct MRR kinetic studies using the Ginstling–Brounstein (GB) and Jander diffusion models under dynamic (via reactor rotation) and static conditions (D-MRR and S-MRR, respectively) at various reduction temperatures and times. The reduction rate and nominal kinetic constants for the d-MRR are found to be more than three times greater than those for the S-MRR, possibly because of the enhanced mass transfer rate in the d-MRR. d-MRR results in superior precursor conversion and pSi yield than S-MRR. The apparent activation energy for d-MRR is approximately 180 kJ mol–1 by GB model. The pSi microparticles are mesoporous (pore size = 23.7 nm, pore volume = 0.30 cm3 g–1) and comprise interconnected primary silicon nanoparticles (SiNPs) (diameter = 30 nm). Therefore, a pSi/C composite anode demonstrates significantly enhanced cycling stability compared with conventional solid SiNP/C composites. Overall, d-MRR is a highly efficient and scalable production process for pSi microparticles for use in high-capacity anodes for advanced lithium-based batteries.