Hierarchical Solvation Chemistry via Ether-Ester-Cosolvent Synergy Enables High-Performance Lithium-Metal Batteries...

Lithium metal batteries (LMBs) offer high energy densities but are frequently plagued by rapid degradation under extreme conditions, such as low temperatures or high C-rates. This performance decay stems primarily from sluggish Li⁺ transport kinetics and high desolvation energy penalties imposed by conventional electrolytes. Herein, we engineer a hierarchically solvating electrolyte system comprising a weakly coordinating ether (tetrahydropyran, THP), a strongly coordinating ester (methyl propionate, MP), and lithium difluoro(oxalato)borate (LiDFOB). This molecular configuration fosters an anion-enriched primary solvation sheath, effectively minimizing the activation energy required for Li⁺ desolvation. Furthermore, the incorporation of trifluorotoluene (TFT) as a non-solvating diluent modulates the local solvation structure toward aggregate dominance, thereby promoting the formation of a compact and homogeneous solid electrolyte interphase (SEI). Through precise compositional tuning, we achieve a robust SEI architecture characterized by the uniform distribution of ductile organic matrices and high-modulus inorganic species. This mosaic structure provides an optimal mechanical balance of rigidity and elasticity, preserving interfacial integrity during prolonged cycling at cryogenic temperatures. Consequently, Li||Li symmetric cells exhibit ultrastable cycling for over 6000 h at -25°C. In Li||LiCoO_2​ full cells, the electrolyte supports 400 stable cycles, retaining 85.5% and 66.2% of the nominal room-temperature capacity at -25°C and -45°C, respectively. These findings offer critical design principles for tailoring solvation chemistry to enable high-performance LMBs in extreme environments.