Unraveling the Origin of Lithiophilicity toward a Molten Li Metal: Zn Metal as Trojan Horse

In this work, we investigated the origin of lithiophilicity of a Cu foil substrate modified by a sputtered Zn thin film (Cu@Zn) in contact with a molten Li metal to understand the reaction mechanism between Li and Cu@Zn. We studied the reaction between the molten Li metal and the Cu surface during Li solidification via in situ scanning electron microscopy (SEM), subsequently performed post-mortem energy dispersive spectroscopy (EDS) and Grazing Incidence X-ray Diffraction (GIXRD) on the coatings to analyze the chemistry of the reaction products, and compared the results for different thicknesses of nanometric Zn films (5-50 nm). For the first time in the literature, we report the existence of a metastable ternary Li-Cu-Zn alloy at 300 °C after the reaction of Cu@Zn with the molten Li metal. We also report the segregation of Cu and Zn by formation of Cu-Zn intermetallic compounds during the cooling down step. The results of our in situ study are pivotal to clarify the interfacial reactions occurring between a lithiophilic current collector and a molten Li metal and have utmost importance for designing advanced anode materials for future solid-state battery applications.