From Interphase to Interface: Revealing the Dynamic Evolution of Interfacial Electrolyte Configuration and Solid Electrolyte Interphase on Lithium Metal Anode at Elevated Temperature

Achieving durable cycling in lithium metal batteries at elevated temperature necessitates a robust interfacial environment. However, the mechanistic understanding of how elevated temperature governs the dynamic evolution of the interfacial electrolyte configuration and the solid electrolyte interphase (SEI) remains limited, hindering rational electrolyte design. Herein, by using surface-sensitive in situ infrared spectroscopies, we directly visualize the escape of anions from the interface, a process driven by interfacial charge imbalance during desolvation. This phenomenon results in the formation of an anion-lean, solvent-rich interface, with the process being significantly accelerated and exacerbated at elevated temperatures. Consequently, more solvent-derived and fewer anion-derived SEI components are formed, resulting in aggravated interfacial resistance and compromised interfacial stability. In this case, both reducing the anion transference number and introducing adsorbed inert cations can mitigate the elevated temperature-aggravated anion escaping from the interface, leading to the restoration of anion-derived LiF components in the SEI, culminating in enhanced interfacial stability and improved cycling behavior. After revealing the correlation between the dynamic evolution of interfacial electrolyte configuration and SEI fabrication, this work enables the precise tuning of electrolyte and interfacial engineering, shifting the focus from empirically modifying the interphase to fundamentally regulating the interface as the origin of SEI formation.