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