Tuning Carbonate Solvation via Electrolyte Engineering Toward Robust Low-Temperature Lithium Metal Batteries

Conventional ethylene carbonate (EC)-based electrolytes are dominated by strong Li+-solvent coordination, which leads to sluggish reaction kinetics at low-temperature and severe interfacial side reactions under high-voltage operation. Herein, a ternary electrolyte with weak-solvation characteristics based on lithium difluoroxalate borate (LiDFOB) salt and synergistic propylene carbonate (PC)/ methyl difluoroacetate (MDFA)/ fluoroethylene carbonate (FEC) (4:4:2, v/v/v) solvent system is developed. MDFA serves as the primary weakly coordinating component to reconstruct the Li+ solvation environment by weakening Li+-PC coordination, while FEC complements this process by promoting the formation of robust inorganic-rich interphases on both electrodes. The reconstructed solvation structure facilitates Li+ desolvation, whereas the stabilized interphases effectively suppress electrolyte decomposition and transition-metal dissolution, leading to a thin and homogeneous cathode electrolyte interphase (∼7 nm) and a low-resistance LiF-rich solid electrolyte interphase. Benefiting from the synergistic regulation of bulk solvation and interfacial chemistry, Li||Li symmetric cells achieve stable cycling over 1000 h at -30 °C, outperforming EC-based electrolytes by ∼400 h. Moreover, Li||NCM811 full cells retain 98.16% capacity after 110 cycles at -30 °C (3.0-4.3 V). This work provides a feasible solvation modulation strategy for high-performance low-temperature lithium metal batteries.