Ionic Liquids Containing Sulfonium Cations as Electrolytes\nfor Electrochemical Double Layer Capacitors

Abstract

In\nthis work, we report on the behavior of ionic liquids (ILs)\ncontaining sulfonium cations as electrolytes for electrochemical double\nlayer capacitors (EDLCs). Physical properties such as viscosity and\nionic conductivity are reported over a range of temperatures for ILs\ncontaining the diethylmethyl sulfonium [S₂₂₁], triethyl\nsulfonium [S₂₂₂], and diethylpropyl sulfonium [S₂₂₃] cations paired with the bis­(trifluoromethanesulfonyl) imide [Tf₂N] anion. The size and structure of the cations are shown\nto influence the physical and electrochemical properties of the ILs,\nwith a significant degree of ionic coordination being evident in [S₂₂₃]­[Tf₂N]. The electrochemical behavior of these\nILs in EDLCs was compared with that of a fairly established IL electrolyte, <i>N</i>-butyl-<i>N</i>-methylpyrrolidinium bis­(trifluoromethanesulfonyl)\nimide ([Pyr₁₄]­[Tf₂N]), and it is shown that\n[S₂₂₁]­[Tf₂N] can perform better in terms of\nenergy and power at room temperature, despite operating at a much\nreduced potential.