The synthesis of a gelled polymer electrolyte (GPE) using poly(ethylene glycol) blending poly(acrylonitrile) (i.e., PAN-b-PEG-b-PAN) as a host, dimethyl formamide (DMF) as a plasticizer and LiClO4 as an electrolytic salt for electric double layer capacitors (EDLCs) is reported. The PAN-b-PEG-b-PAN copolymer in the GPE has a linear configuration for high ionic conductivity and excellent compatibility with carbon electrodes. When assembling the GPE in a carbon-based symmetric EDLC, the copolymer network facilitates ion motion by reducing the equivalent series resistance and Warburg resistance of the capacitor. This symmetric cell has a capacitance value of 101 F g−1 at 0.125 A g−1 and can deliver an energy level of 11.5 Wh kg−1 at a high power of 10 000 W kg−1 over a voltage window of 2.1 V. This cell shows superior stability, with little decay of specific capacitance after 30 000 galvanostatic charge-discharge cycles. The distinctive merit of the GPE film is its adjustable mechanical integrity, which makes the roll-to-roll assembly of GPE-based EDLCs readily scalable to industrial levels.