Effect of precursor morphology on the electrochemical performance of porous Si anodes prepared by magnesiothermic reduction

The magnesiothermic reduction of SiO ₂ to Si is a promising route for preparing high-energy-density Si-based anode materials for lithium-ion batteries. However, the effect of the initial morphological properties of SiO ₂ on the electrochemical performance of Si remains unclear. Herein, porous Si (PSi) particles were prepared from four different SiO ₂ precursors, namely, spherical SiO ₂ particles with diameters of 0.3 and 20 μm (denoted SiO ₂-0.3 and SiO ₂-20, respectively), fumed SiO ₂ powder (denoted SiO ₂-F), and well-ordered mesoporous SiO ₂ particles (denoted SiO ₂-K). Highly crystalline PSi particles were obtained after magnesiothermic reduction and subsequent HCl and HF etching. PSi prepared from SiO ₂-0.3 maintained its precursor morphology to some extent, whereas highly irregular Si particles were produced from SiO ₂-20, SiO ₂-F, and SiO ₂-K. Among the PSi particles, those prepared from SiO ₂-0.3 delivered the highest reversible capacity (1427 mAh g ^–1 at 0.1 A g ^–1) after 50 discharge–charge cycles. Because of the unique hierarchically porous morphology of PSi prepared from SiO ₂-0.3, the expansion of its electrode thickness was suppressed below 140 %. Moreover, owing to its nanosized Si domains and good electrode wetting, PSi prepared from SiO ₂-0.3 demonstrated improved electrochemical properties compared with those prepared from SiO ₂-F and SiO ₂-K.