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 degrees C for the cold wing and simultaneously guaranteed its flash point at >+150 degrees 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 degrees C as an ambient cold, -74 degrees C as a deep cold, and +80 degrees C as a deep hot.