Endowing the Operability of Supercapacitors at High Temperatures by Regulating the Solvation Structure in Dilute Hybrid Electrolyte with Trimethyl Phosphate Cosolvent

The redox stabilities of different oxygen donor solvents (C═O, P═O and S═O) and lithium salt anions for supercapacitors (SCs) electrolytes have been compared by calculating the frontier molecular orbital energy. Among six lithium difluoro(oxalate)borate (LiDFOB)‐based mono‐solvent electrolytes, the dilute LiDFOB‐1,4‐butyrolactone (GBL) electrolyte exhibits the highest operating voltage but suffers from electrolyte breakdown at elevated temperatures. Trimethyl phosphate (TMP) exhibits the highest redox stability and a strongly negative electrostatic potential (ESP), making it suitable for promoting the dissolution of LiDFOB as expected. Therefore, TMP is selected as a co‐solvent into LiDFOB‐GBL electrolyte to regulate Li+ solvation structure and improve the operability of electrolytes at high temperatures. The electrochemical stable potential window (ESPW) of 0.5 m LiDFOB‐G/T(5/5) hybrid electrolyte can reach 5.230 V. The activated carbon (AC)‐based symmetric SC using 0.5 m LiDFOB‐G/T(5/5) hybrid electrolyte achieves a high energy density of 54.2 Wh kg−1 at 1.35 kW kg−1 and the capacitance retention reaches 89.2% after 10 000 cycles. The operating voltage of SC can be maintained above 2 V when the temperature rises to 60 °C. A ternary lithium difluoro(oxalato)borate (LiDFOB)‐1,4‐butyrolactone (GBL)‐trimethyl phosphate (TMP) hybrid electrolyte is proposed to construct high‐voltage supercapacitors with wide operating temperature range. GBL acts as the main solvent to promote ion migration due to its high dielectric constant, while TMP as the co‐solvent to regulate the Li+ solvation structure due to its high donor number.