Propionitrile as a single organic solvent for high voltage electric double-layer capacitors

Abstract

This study investigates the novel use of propionitrile (PN) as the single organic solvent for high-voltage carbon/carbon capacitors. Quaternary ammonium salts spiro-(1,1ʹ)-bipyrrolidinium tetrafluoroborate (SBPBF4) and 1,1-dimethylpyrrolidinium tetrafluoroborate (DMPBF4) dissolved in acetonitrile (AN) and propionitrile (PN) are compared. PN-based electrolytes exhibit a large and symmetric electrochemical stability, an exceptional anodic potential limit, good ionic conductivity, and low viscosity, allowing EDLCs to operate at 3.5 V even with a high current density (2.5 A g−1). Moreover, PN-based electrolytes can suppress the anodic dissolution of the Al current collector at a high potential. These advantages help in the realization of EDLCs with excellent cycling stabilities at high voltages. As a result, at 3.5 V, EDLCs with PN-based electrolytes exhibit the highest energy and power density of 49.3 Wh kg−1 and 22.9 kW kg−1, respectively. Therefore, the electrolyte systems reported here could be a promising electrolyte candidate to replace currently commercialized electrolytes for practical applications.