No abstract

In this work, we report on the behavior of ionic liquids (ILs) containing sulfonium cations as electrolytes for electrochemical double layer capacitors (EDLCs). Physical properties such as viscosity and ionic conductivity are reported over a range of temperatures for ILs containing the diethylmethyl sulfonium [S 221 ], triethyl sulfonium [S 222 ], and diethylpropyl sulfonium [S 223 ] cations paired with the bis-(trifluoromethanesulfonyl) imide [Tf 2 N] anion. The size and structure of the cations are shown to influence the physical and electrochemical properties of the ILs, with a significant degree of ionic coordination being evident in [S 223 ][Tf 2 N]. The electrochemical behavior of these ILs in EDLCs was compared with that of a fairly e s t a b l i s h e d I L e l e c t r o l y t e , N -b u t y l -N -m e t h y l p y r r o l i d i n i u m b i s -(trifluoromethanesulfonyl) imide ([Pyr 14 ][Tf 2 N]), and it is shown that [S 221 ][Tf 2 N]can perform better in terms of energy and power at room temperature, despite operating at a much reduced potential.

Given their relevant physicochemical properties, ionic liquids (ILs) are attracting great attention as electrolytes for use in different electrochemical devices, such as capacitors, sensors, and lithium ion batteries. In addition to the advantages of using ILs containing lithium cations as electrolytes in lithium ion batteries, the Li(+) transport in ILs containing the most common anion, bis(trifluoromethanesulfonyl) imide anion ([Tf2N]), is reportedly small; therefore, its contribution to the overall conductivity is also low. In this work, we describe the preparation and characterization of two new and one known IL containing the tetracyanoborate anion ([B(CN)4]) as the anionic species. These ILs have high thermal and chemical stabilities, with almost twice the ionic conductivity of the [Tf2N] ILs and, most importantly, provide a greater role for the Li(+) ion throughout the conductivity process. The experimental ionic conductivity and self-diffusion coefficient data show that the [B(CN)4]-based ILs and their Li(+) mixtures have a higher number of charge carriers. Molecular dynamics simulations showed a weaker interaction between Li(+) and [B(CN)4] than that with [Tf2N]. These results may stimulate new applications for ILs that have good Li(+) transport properties.