Strong Solvent and Dual Lithium Salts Enable Fast-Charging Lithium-Ion Batteries Operating from -78 to 60 °C

Current lithium-ion batteries degrade under high rates and low temperatures due to the use of carbonate electrolytes with restricted Li⁺ conduction and sluggish Li⁺ desolvation. Herein, a strong solvent with dual lithium salts surmounts the thermodynamic limitations by regulating interactions among Li⁺ ions, anions, and solvents at the molecular level. Highly dissociated lithium bis(fluorosulfonyl)imide (LiFSI) in dimethyl sulfite (DMS) solvent with a favorable dielectric constant and melting point ensures rapid Li⁺ conduction while the high affinity between difluoro(oxalato)borate anions (DFOB^-) and Li⁺ ions guarantees smooth Li⁺ desolvation within a wide temperature range. In the meantime, the ultrathin self-limited electrode/electrolyte interface and the electric double layer induced by DFOB^- result in enhanced electrode compatibility. The as-formulated electrolyte enables stable cycles at high currents (41.3 mA cm^-2) and a wide temperature range from -78 to 60 °C. The 1 Ah graphite||LiCoO₂ (2 mAh cm^-2) pouch cell achieves 80% reversible capacity at 2 C rate under -20 °C and 86% reversible capacity at 0.1 C rate under -50 °C. This work sheds new light on the electrolyte design with strong solvent and dual lithium salts and further facilitates the development of high-performance lithium-ion batteries operating under extreme conditions.