An energy storage device includes an anode, a cathode, and a separator disposed between the anode and the cathode. At least one of the anode, cathode and separator includes a copolymer functioning as a non-aqueous adhesive and/or solid-state electrolyte for the energy storage device. The copolymer is a copolymer or a derivative thereof, which is produced by polymerization of monomers containing conductive ion group and/or olefinic monomers in the presence of 2-propenenitrile. Therefore, the energy storage device which the copolymer is used therein has excellent charging and discharging performance to therefore effectively enhance the efficiency and extend the service life of the energy storage device.