Performance of electric double layer capacitors with gel electrolytes containing an asymmetric ammonium salt

Polymer gel electrolytes, composed of poly(vinylidene fluoride) (PVdF) and propylene carbonate (PC) as a plasticizer with the asymmetric ammonium salt triethylmethylammonium tetrafluoroborate (TEMABF(4)), have been applied to electric double layer capacitors (EDLCs) with activated carbon cloth elect rodes. The present capacitors with TEMABF(4) have a higher capacitance, bet ter coulombic efficiency, and lower leak current than those with a typical electrolytic salt, tetraethylammonium tetrafluoroborate (TEABF(4)). Ac impe dance measurements show that the capacitors with TEMABF4 have not only lowe r electrolyte-bulk resistances but also lower electrolyte/electrode-interfa ce resistances in comparison with the capacitors with TEABF(4).