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

• Mg catalysts were found to enable the growth of Silicon nanowires (Si NWs) via a vapor-solid-solid (VSS) mechanism, with the formation of Mg 2 Si as an intermediate product. • This VSS mechanism allowed enhanced Si NWs growth density (0.8 mg/cm 2 ) and diameter refinement compared to vapor-liquid-solid (VLS) NWs. • Si NWs exhibited high gravimetric (2792 mAh/g) and areal capacities (1.58 mAh/cm 2 ) on planar substrates. • The reversible capacities are competitive with state-of-the-art Si NWs electrodes, while removing the requirement for scarce and expensive catalyst materials. 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 glassware-based setup. Analysis of the Si NWs revealed the presence of Mg 2 Si 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/cm 2 ) 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/cm 2 ). The approach highlights Mg as a catalyst for the development of higher mass loading and binder-free Si NWs anodes for LIBs.