Highly conductive electrolytic solution for electric double-layer capacitor using dimethylcarbonate and spiro-type quaternary ammonium salt

Use of a novel electrolyte, a spiro-type quaternary ammonium salt (SBP-BF4), in an electric double-layer capacitor (EDLC) has allowed the use of a linear-structure carbonate-which, although it has a low viscosity, had never been used as a solvent because it does not dissolve a conventional electrolyte-as a sub-solvent for an electrolytic solution in combination with a main solvent, propylenecarbonate (PC). Of such linear-structure carbonates, use of dimethyl-carbonate (DMC) in an electrolytic solution attains not only low viscosity but also high conductivity of an electrolytic solution. Furthermore, an EDLC using the electrolytic solution exhibits very excellent capacitance, internal resistance, temperature properties, and discharging rate.