Leakage currents and self-discharge of ionic liquid-based supercapacitors

Ionic liquid (IL)-based supercapacitors have been widely demonstrated to outperform electrochemical double-layer capacitors (EDLCs) working with conventional organic electrolytes in terms of specific energy and operating voltage. Here, the results of a study on the leakage currents (Ileak) and self-discharge energy loss factors (SDLF) of IL-based EDLCs at different cell voltages up to 3.2 V and at 30 and 60 C are reported. Cells assembled with the N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI) and N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide pure ILs and a mixture of PYR14TFSI and propylene carbonate (PC) 1 to 1 molar were tested. The results are compared to those achieved with EDLCs featuring the conventional 1 M tetraethyl ammonium tetrafluoroborate (Et4NBF4)-PC electrolyte. The study demonstrates that ILs provide Ileak and SDLF that are lower than those obtained with the latter electrolyte, with PYR14TFSI allowing the lowest values