High performance solid-state supercapacitors based on highly conductive organogel electrolyte at low temperature

Solid-state supercapacitors have advantages of leakage free and flexibility but usually have low energy density at low temperature. This is largely due to the significantly declined ionic conductivity as well as the relatively low voltage window of the gel electrolytes. Here we designed a low temperature tolerant organogel electrolyte by systematically tuning the solvents’ ionic conductivity, melting point and electrochemical stability via acetonitrile (AN), methyl formate (MF), and propylene carbonate (PC), respectively. The tuned gel electrolyte of polymer metrix of poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) with salt of ionic electrolyte 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) exhibited ionic conductivity of 2.95 mS cm−1, mechanical strain rate of 350% and voltage window of 0–4 V at low temperature of −60 °C. The stack cell of solid-state supercapacitor using activated carbon as electrode films exhibited capacitance retention of 98.5% at −60 °C compared with that under room temperature, a 3.9% capacitance attenuation after 10,000 charge/discharge cycles, and exceptional stack energy density of 30.8 Wh kg−1, at least three times higher than the state-of-the-art solid-state supercapacitors.