Electrochemical capacitors with polymer electrolytes based on ionic liquids

A series of electrochemical capacitors, based on carbon powders (specific surface area 830 and 2600 m2/g) as an electroactive material, applying polymer–ionic liquid (IL) solid electrolytes were prepared and tested. Both polymer electrolytes as well as capacitor electrodes, in the form of thin foils, were prepared by a casting technique. All-plastic capacitors, having a coin-like shape, a diameter of 18 mm and a mass of ca. 200–900 mg, were constructed by sandwiching a polymer electrolyte between two electrodes. Ionic liquids: 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-1-methylpyrrolidinium bis(trifluoromethane sulfonyl) imide and 1-butyl-3-methylimidazolium hexafluorophosphate served both as sources of ions as well as polymer plasticisers. In some cases, sulpholane was added to the system as an additional plasticiser. The performance of capacitors was determined by cyclic voltammetry, impedance spectroscopy and galvanostatic charging and discharging. Specific capacity was in the range of 4.2–7.7 μF/cm2, calculated per total surface of the carbon materials, and up to 200 F/g expressed versus the mass of carbon material.