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Adiponitrile (ADN) has recently received extensive attention as a solvent for energy storage devices due to its significantly high flash point and stabilizing ability against oxidation of electrolytes at high voltages. A free standing and flexible gel polymer electrolyte (GPE) film has been reported containing a mixture of ADN and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) immobilized in poly(vinylidene fluoride-co-hexafluoropropylene) for application in electrical double-layer capacitors (EDLCs). The GPE containing 5 mol % LiTFSI in ADN shows excellent characteristics in terms of thermal stability (∼120 °C), wider electrochemical stability window (∼3.92 V versus Ag), and high ionic conductivity (∼1.97 × 10 −3 S cm −1 at room temperature). The EDLC is fabricated with an ADN-based GPE film sandwiched between symmetric electrodes of activated carbon (derived from a waste biomass pinecone). The EDLC has been electrochemically characterized by electrochemical impedance spectroscopy, cyclic voltammetry, and charge−discharge tests. The specific capacitance of the capacitor has been observed to be 225−241 F g −1 , which corresponds to a specific energy of 31.2−34.0 Wh kg −1 and a maximum specific power of 15.4−18.0 kW kg −1 . The EDLC illustrates stable performance for ∼20 000 cycles of galvanostatic charge−discharge with ∼80% capacitance retention and 96−100% Coulombic efficiency. The capacitor gives stable performance for a temperature range of −30 to 90 °C.