A Fluorine-Free Solvent Based on Dual Descriptors for Ultrawide-Temperature Lithium Metal Batteries (-105°C to 70°C).

Abstract

Fluorinated solvents are widely employed in electrolytes for lithium metal batteries (LMBs) due to their broad liquid-phase temperature range. However, their use entails significant challenges, including undesirable interfacial parasitic reactions at elevated temperatures and lithium-salt precipitation at low temperatures. In this study, we propose a fluorine-free electrolyte design strategy based on synergistic optimization of molecular geometry and electron density distribution. The tailored solvent, 2-ethylbutyl acetate (2EA), plays a critical role in modulating intermolecular interactions and Li⁺ coordination. The 2-ethylbutyl group introduces substantial steric hindrance while exerting electron-donating inductive effects, thereby effectively weakening the binding affinity between carbonyl oxygen and Li⁺. Concurrently, steric hindrance inhibits intermolecular interaction of solvent molecules at cryogenic temperatures, resulting in an ultra-low melting point (below -100°C). Furthermore, the synergistic steric and electronic effects reorganize the solvation structure into an anion-dominated configuration, facilitating Li⁺ desolvation and promoting a robust, inorganic-rich interphase. As a result, the 2EA-based electrolyte enables high-voltage Li||LiCoO₂ cells to achieve exceptional cycling stability (80% capacity retention after 1500 cycles at 25°C), remarkable rate capability (90% capacity retention at 10°C), and stable operation over an ultrawide temperature range from -60°C to 70°C.