A tailor-made deep eutectic solvent for 2.2 V wide temperature-tolerant supercapacitors via optimization of N,N-dimethylformamide/water co-solvents.

A high-performing electrolyte plays an imperative role in the pursuit of high energy density, green, low-cost, and safe supercapacitors. To this end, a novel deep eutectic solvent (DES) composed of N-methylacetamide and lithium perchlorate has been engineered by the addition of co-solvents including water and N,N -dimethylformamide (DMF). Interestingly, each co-solvent makes a specific contribution to DES performance as water for flame resistance and DMF for antifreeze. The optimized hybrid DES is tested as the electrolyte for symmetric supercapacitors with polyaniline/reduced graphene oxide composite electrodes (PANI-rGO). The hybrid DES with high ionic conductivity imparts a high operation voltage of 2.2 V to devices whereas the PANI-rGO electrode with the pseudocapacitive behavior provides the high capacitances. Due to the above synergistic effects, our device delivers the maximum energy density of 28.2 W h kg−1 at a power density of 1.1 kW kg−1 and shows moderate cyclic stability at room temperature. More importantly, the supercapacitors can well function in a low temperature range from −20 to 25 °C. The device operated at 25 °C achieves the maximum capacitance of 41.9 F g−1 due to improved ionic conductivity of the DES electrolyte. The current study opens a new route towards sustainable and affordable energy storage devices. [Display omitted] • DES electrolyte with N,N -dimethylformamide as co-solvent shows 2.2V window. • PANI-rGO exhibits pseudocapacitive behavior in the hybrid DES electrolyte. • Fabricated symmetric supercapacitor has potential to operate from −20 to 70 °C. • It delivers an energy density of 28.2 W h kg−1 at a power density of 1.1 kW kg−1 [ABSTRACT FROM AUTHOR]