Hierarchical Solvation Chemistry via Ether–Ester–Cosolvent Synergy Enables High‐Performance Lithium‐Metal Batteries at a Low Temperature

Overview

Lithium metal batteries exhibit degradation under extreme operational conditions, particularly at low temperatures and high charge rates, due to kinetic limitations in Li+ transport and high desolvation energy barriers imposed by conventional electrolytes. This study presents a hierarchically solvating electrolyte formulation designed to overcome these constraints through molecular engineering of the solvation sheath and solid electrolyte interphase architecture.

Methods and approach

The electrolyte system was engineered using a three-component solvating framework: tetrahydropyran as a weakly coordinating ether, methyl propionate as a strongly coordinating ester, and lithium difluoro(oxalato)borate as the salt. Trifluorotoluene was incorporated as a non-solvating diluent to modulate solvation structure dynamics. This compositional hierarchy was designed to generate an anion-enriched primary solvation sheath, reducing Li+ desolvation activation energy and promoting aggregate-dominated solvation. The resulting solid electrolyte interphase was characterized through analysis of its organic and inorganic component distribution and mechanical properties. Electrochemical performance was evaluated using Li||Li symmetric cells and Li||LiCoO2 full cells across multiple temperature regimes ranging from room temperature to -45°C.

Results

Li||Li symmetric cells demonstrated stable cycling exceeding 6000 hours at -25°C. Full Li||LiCoO2 cells sustained 400 consecutive cycles at -25°C with 85.5% capacity retention relative to room-temperature nominal capacity, and 66.2% retention at -45°C. The solid electrolyte interphase exhibited a composite architecture with uniform distribution of ductile organic matrices and high-modulus inorganic species, providing mechanical balance between rigidity and elasticity. This microstructural configuration maintained interfacial stability during extended cryogenic cycling.

Implications

The hierarchical solvation design principles demonstrated establish a generalizable framework for electrolyte engineering targeted at extreme-environment battery operation. The anion-enriched solvation sheath architecture and aggregate-dominated solution structure represent critical control parameters for minimizing kinetic barriers in low-temperature regimes. The mechanical properties of the composite SEI indicate that optimization of organic-inorganic component distribution constitutes a viable strategy for preserving interface integrity across repeated electrochemical cycles at cryogenic temperatures.