Solvent-free double-layer capacitors with polymer electrolytes based on 1-ethyl-3-methyl- imidazolium triflate ionic liquid

A series of electrochemical capacitors based on carbon powders (specific surface areas 830 and 2600 m2/g) and polymer electrolytes were constructed 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 were coin-shaped, with a diameter of 12–18 mm and a mass of ∼100–500 mg, and were constructed by sandwiching the polymer electrolyte between two electrodes. An ionic liquid, 1-ethyl-3-methyl-imidazolium triflate, served both as a source of ions as well as a polymer plasticiser. In some cases, sulpholane was added to the system as an additional plasticiser. Poly(acrylonitrile), poly(vinylidenefluoride), and its copolymer with hexafluoropropylene, poly(ethylene oxide), poly(vinyl alcohol) as well as poly(methylmethacrylate) served as a polymer matrix. Polymer electrolytes showed conductivity up to 16 mS/cm. The performance of the capacitors was determined by cyclic voltammetry, impedance spectroscopy and galvanostatic charging/discharging. Specific capacity was up to 230 F/g, expressed versus the mass of the carbon material.