High performance spiro ammonium electrolyte for Electric Double Layer Capacitors

The smallest spiro ammonium salt reported to date, 1 M 4-Axoniaspiro[3,4]octane tetrafluoroborate (APBF4), was successfully synthesized and investigated as the electrolyte with acetonitrile (AN) in an Electric Double Layer Capacitor (EDLC) for the first time. The electrochemical characteristics of EDLC devices containing 1 M APBF4/AN paired with commercial activated carbon electrodes were compared to devices containing popular EDLC electrolytes, 1 M 5-Azoniaspiro[4.4]nonane tetrafluoroborate (SBPBF4/AN) and 1 M tetraethyl ammonium tetrafluoroborate (TEABF4/AN), using cyclic voltammetry (CV), galvanostatic charge discharge (GCD), and electrochemical impedance spectroscopy (EIS). The average gravimetric capacitance of the 1 M APBF4 device (124.7 F g−1) was found to be greater than the values measured for both the 1 M SBPBF4 device (108.6 F g−1) and the 1 M TEABF4 device (99.2 F g−1). The direct current equivalent series resistance (ESR) of the 1 M APBF4 device (383.4 mΩ cm−2) was found to be substantially lower than the values measured for both the 1 M SBPBF4 device (501.0 mΩ cm−2) and the 1 M TEABF4 device (710.8 mΩ cm−2). These results demonstrate that APBF4, when compared to current commercial electrolytes, significantly enhances the energy storage properties of EDLC devices.