Mg-Coated Si Thin Film As Model Electrode for Mechanistic Study of Li-Mg-Si Zintl Phase Formation in Lithium-Ion Batteries

Silicon (Si) is a promising anode material for high energy density lithium-ion batteries (LIBs) but its poor cycling performance prevents its large-scale adoption. Introducing Mg salt into the electrolyte has shown to form a ternary Li-Mg-Si Zintl phase upon lithiation of Si and improve the cycling stability; however, its formation mechanism and impacts on the solid electrolyte interphase (SEI) are not yet well understood. Herein, we demonstrate the formation of a ternary Li-Mg-Si Zintl phase via a Magnesium (Mg) coated Si thin film electrode, where Mg diffuses into the Si film upon deposition and in the lithiation process. The Zintl phase alters the nature of SEI, suppresses the excess decomposition of electrolyte and improves the capacity retention of the Si anode. This study provides insights into the formation mechanism of ternary Zintl phase and guidelines for the future design of Si anodes.