A new polymer electrolyte poly(acrylonitrile)–dimethylsulphoxide–salt for electrochemical capacitors

The PAN–DMSO–Et4NBF4 and PAN–DMSO–Et4NTf (Tf is triflate ion) electrolytes were prepared as white, turbid foils with a thickness in the range of 0.1–0.5 mm, using the casting technique. Room temperature conductance of the electrolytes, detected from ac impedance experiments, was at the level of 8 and 14 mS cm−1 for Et4NBF4 and Et4NTf salts, respectively. The electrochemical stability window of approximately 2.6–2.8 V was estimated using a glassy carbon electrode. Temperature dependence of the conductivity is of the Arrhenius-type for both electrolytes, with an activation energy of approximately 34 kJ mol−1. The double-layer capacitors built with these electrolytes, serving both as separators and activated carbon powder (ACP) binders, showed a specific capacity of 50 F g−1 of carbon material. Capacitors were assembled by sandwiching the PAN–DMSO–salt electrolyte between two PAN–salt–DMSO–ACP–AB electrodes and pressing across the system; the resulting devices had a coin-like shape with 8 mm diameter and thickness between 2.0 and 2.5 mm.