Electrolytic Properties of Quaternary Ammonium Salts with Difluoro(oxalato)borate Anions and Its Application to Electric Double Layer Capacitors

Introduction EDLC (electric double layer capacitor) is an energy storage device utilizing an electric double layer formed in an electrode | electrolyte interphase. The use of the small quaternary ammonium ion can increase the number of ions accumulated in pores of an activated carbon electrode and obtain high capacitance. We synthesized tetramethylammonium tetrafluoroborate (TMABF4) with relatively small cation size. The solubility of TMABF4 in propylene carbonate (PC) was below 0.1 mol dm at 25°C. In the previous paper, it was found that tetramethylammonium difluoro(oxalato)borate(TMADFOB) with unsymmetrical anion synthesized by us shows higher solubility more than 1.6 mol dm in PC at 25°C. In this paper, we report electrolytic properties of concentrated TMADFOB and its application to electric double layer capacitors.