Enhancing Stability in Acetonitrile-Based Supercapacitors: Implementation of Di-Pyrrolidinium Ionic Salts

One of the main strategies to enhance the energy density of electrochemical double layer capacitors (EDLCs) is to surpass the limitations of traditional electrolyte operating voltages. In our study, a novel high-purity di-pyrrolidine based electrolyte salt, 1-butyl-3-dimethylpyrrolidinium di[bis(trifluoromethanesulfonyl)imide] (C4di [mPyr].di[TFSI]) is synthesized, and high voltage electrolyte using acetonitrile (AN) as the sole solvent is prepared for EDLCs. The 0.5 M C4di[mPyr].di[TFSI]/AN electrolyte demonstrates an impressive electrochemical stability window of 6.04 V and a high operating voltage of 3.4 V, which is almost the highest stability reported so far for low concentration AN-based electrolytes. The impedance and conductivity of the 0.5 M C4di[mPyr].di [TFSI]/AN electrolyte are highly comparable to commercial 1.0 M TEA.BF4/AN electrolyte. EDLCs equipped with the electrolyte can maintain specific capacitance retentions of 94.92 % and 77.78 % after 2000 cycles at 3.4 V and 3.6 V, respectively. Besides, the GC-MS and XPS further prove its stability and confirm the possible electrochemical reactions of the C4di[mPyr].di[TFSI]/AN electrolyte on the electrode surface under the polarized voltages. Furthermore, the XPS also appears to show a relatively weak interaction between TFSI- and the electrode, which may serve as a potential factor in inhibiting the hydrolysis of TFSI- and the polymerization of AN.