Freeze‐Vulnerable Plastic Crystal to Cryogenic Liquid Electrolyte for Lithium Batteries by Deep Freezing‐Point Depression

Abstract Low‐ T _f solvents ( T _f = freezing point) are considered and employed for low‐temperature lithium‐ion battery (LIB) electrolytes to keep electrolytes in the liquid phase at low temperatures. Unfortunately, T _f is synchronized with T _b (boiling point) so low T _f brings T _b down and therefore discourages the thermal stability of electrolytes using low‐ T _f solvents. In this work, 1) the hot wing of LIB‐working temperature by employing a high‐ T _b (inevitably high‐ T _f ) solvent and 2) the cold wing by using a significant T _f depression is secured. Sulfolane is employed as the high‐ T _f (therefore, high‐ T _b ) and high‐ K _f ( K _f = cryoscopic constant) solvent since its mesomorphic state between solid and liquid. That abnormally and significantly decreases the enthalpy of fusion, and resultantly grants extremely high K _f at 66.4 K m ⁻¹ . By employing sulfolane with 2 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the liquid‐phase temperature window down to <−80 °C for the cold wing and simultaneously guaranteed its flash point at >+150 °C for the hot wing is successfully extended. LIB cells with lithium iron phosphate and lithium metal worked in a good stand with 2 m LiTFSI/sulfolane at room temperature, −30 °C as an ambient cold, −74 °C as a deep cold, and +80 °C as a deep hot.