Molecular Design of Electrolytes toward a Robust Cathode−Electrolyte Interphase for 4.5 V Lithium Metal Batteries under Extreme Operating Conditions

High-energy-density lithium batteries increasingly operate under high voltage and fast charging, with interfacial stability and reaction kinetics at elevated temperature becoming critical bottlenecks. Conventional electrolytes undergo severe parasitic reactions, leading to transition-metal dissolution, increased interfacial resistance, and rapid capacity fading, which hinder simultaneous stability and rate capability. Here, an electrolyte design combining molecular engineering and interfacial regulation is proposed. An α-H-free ester solvent, methyl 2-fluoro-2-methylpropanoate (MFMP), enhances oxidative stability, while its weak solvation reshapes the Li⁺ solvation structure and promotes anion participation, forming an inorganic-rich cathode electrolyte interphase (CEI). A functional additive, ethylene sulfate (DTD), further regulates interfacial reactions at elevated temperatures, leading to a more uniform interphase and lower charge-transfer resistance. The electrolyte delivers stable cycling and improved rate performance at 4.5 V and maintains low resistance and stable capacity at 45 °C. Structural analysis reveals suppressed cathode degradation and reduced parasitic reactions. This work establishes a multiscale strategy linking molecular design, solvation, and interfacial chemistry for batteries under extreme conditions.