Vapor-solid-solid growth of silicon nanowires using magnesium seeds and their electrochemical performance in Li-ion battery anodes

The energy density of next-generation lithium-ion batteries (LIBs) can be considerably improved by replacing traditional graphite anodes with silicon nanowires (Si NWs). However, the synthesis of Si NWs is restricted due to the requirement for expensive and heavy metal catalysts for growth. Herein, for the first time, we successfully demonstrate the growth of Si NWs using magnesium (Mg) as a catalyst material, within a wet-chemical glass-ware-based setup. Analysis of the Si NWs revealed the presence of Mg2Si at the tips of the Si NWs, indicating that growth proceeds via a vapor–solid-solid (VSS) mechanism. Si NWs were also grown from Mg foil, Mg powder, and from thermally evaporated layers on stainless steel substrates, demonstrating the versatility of Mg as a catalyst material. Mg as a catalyst facilitated high NW mass loadings (up to 0.8 mg/cm2 ) on planar stainless steel current collectors, coupled with tight diameter control (average diameter of ~20 nm). Within LIB half-cell testing, they demonstrated high initial coulombic efficiencies (up to ~81 %) and high gravimetric (up to 2792 mAh/g) and areal capacities (up to 1.58 mAh/cm2 ). The approach highlights Mg as a catalyst for the development of higher mass loading and binder-free Si NWs anodes for LIBs.