Advanced Ultralow‐Concentration Electrolyte for Wide‐Temperature and High‐Voltage Li‐Metal Batteries

High‐voltage Li‐metal batteries (LMBs) are regarded as next‐generation high‐energy‐density storage devices to apply to extensive fields such as electric vehicles, space explorations, subsea operations, and grid‐scale storages. Unfortunately, their practical applications are restricted by some defects of commercial carbonate electrolytes including flammability, low oxidation stability, narrow temperature operation window, and Li dendrites growth. Herein, a novel ultralow‐concentration electrolyte (ULCE, 0.1 m) is fabricated by dissolving lithium difluoro(oxalato)borate in N‐methyl‐N‐methoxyethyl‐pyrrolidinium bis(trifluoromethylsulfonyl)imide ([MEMP][TFSI]) ionic liquid and 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropylether. This advanced ULCE exhibits impressive merits including low cost, non‐flammability, wide operation temperature (−100 to +70 °C), and high electrochemical window (5.75 V). Meanwhile, it helps to suppress Li dendrite growth due to the combined effect of the cation shielding by MEMP+ cations and robust solid electrolyte interphase formed by the preferential decomposition of DFOB− and TFSI− anions. The LiNi0.6Co0.2Mn0.2O2 (NCM622)/Li cell with ULCE shows outstanding performance under a high voltage of 4.5 V and a wide temperature range from −60 to 70 °C. This work provides a distinctive sight to design advanced electrolyte for lower cost, safe, and wide‐temperature high‐energy‐density LMBs. An advanced ultralow‐concentration electrolyte (ULCE) is fabricated by dissolving 0.1 m LiDFOB in ionic liquid and hydrofluoroether. The ULCE shows low cost, non‐flammability, good electrochemical stability, and a wide temperature window. Owing to the unique solvation structure in this ULCE, Li anode paired with high‐voltage cathode affords outstanding performances at a wide temperature range from −60 to 70 °C.