High-conversion reduction synthesis of porous silicon for advanced lithium battery anodes

•A rotational magnesiothermic reduction (R-MR) system is devised for porous silicon (pSi).•The R-MR gives almost complete conversion of precursor and ultra-high yield of pSi.•pSi/C composites and their hybrids with graphite demonstrate stable cycling for ∼600 cycles.•High-conversion R-MR provides a very efficient and scalable process for pSi for high-energy LIBs. For practical implementation of high-capacity silicon anodes, porous silicon (pSi) structures have demonstrated outstanding cycling stability against the large volume changes typical of solid silicon particles. The conventional magnesiothermic reduction (MR) of silica under static conditions limits the yield of pSi and sometimes produces low-purity of pSi owing to limited mass transfer and many side reactions. Hence, we devise a rotational MR (R-MR) system with rapid magnesium transport in which a uniform Mg/SiO2 molar ratio is readily achievable, and a short reaction time can be applied. Compared to conventional MR, the R-MR process has an extremely high yield (∼90 wt%) of pSi at almost complete conversion of precursor, whereas side reactions are substantially suppressed. Mg 2p X-ray photoelectron spectroscopy analysis of the reduction product reveals that pSi yield is well correlated with the conversion of Mg to MgO. The carbon-coated pSi/C samples and their hybrids with graphite (pSi/C@Gr) composites demonstrate stable cycling performance for 300−600 cycles at high capacity with high cycling efficiency (∼99.9%). Therefore, high-conversion R-MR can be a very efficient and scalable process for obtaining pSi for use in carbon composites (such as pSi/C and pSi/C@Gr) that offer outstanding cycling performance in high-capacity anodes for high-energy LIBs. A rotational magnesiothermic reduction (R-MR) system exhibites ultra-high conversion of precursor and yield of porous silicon that can be used as advanced lithium-ion battery anodes. [Display omitted]