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

Abstract

AbstractLow‐Tf solvents (Tf = 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, Tf is synchronized with Tb (boiling point) so low Tf brings Tb down and therefore discourages the thermal stability of electrolytes using low‐Tf solvents. In this work, 1) the hot wing of LIB‐working temperature by employing a high‐Tb (inevitably high‐Tf) solvent and 2) the cold wing by using a significant Tf depression is secured. Sulfolane is employed as the high‐Tf (therefore, high‐Tb) and high‐Kf (Kf = 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 Kf 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.