Ionic Liquids Containing Sulfonium Cations as Electrolytes for Electrochemical Double Layer Capacitors

Anthony J R Rennie,Roberto M Torresi,Vitor L Martins,Peter J Hall

doi:10.1021/acs.jpcc.5b08241

Anthony J R Rennie, Roberto M Torresi + Show 2 more

Open Access

https://doi.org/10.1021/acs.jpcc.5b08241

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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 [S221], triethyl sulfonium [S222], and diethylpropyl sulfonium [S223] cations paired with the bis(trifluoromethanesulfonyl) imide [Tf2N] 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 [S223][Tf2N]. The electrochemical behavior of these ILs in EDLCs was compared with that of a fairly established IL electrolyte, N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide ([Pyr14][Tf2N]), and it is shown that [S221][Tf2N] can perform better in terms of energy and power at room temperature, despite operating at a much reduced potential.

Highlights

IntroductionElectrochemical double-layer capacitors (EDLCs) are a class of energy storage devices known for their high-power densities (up to 10 kW kg−1).[1−3] Their ability to accept or deliver charge at substantially higher rates than electrochemical cells suitable for use in applications where peak demand is substantially greater than the average load.[4,5] Other desirable features of EDLCs are that they possess long cycle life (in excess of 500000 cycles) and relatively high energy efficiencies.[1−7] EDLCs can be used to produce systems that require less maintenance than those where energy is stored in batteries.Conventional EDLCs are comprised of activated carbonbased electrodes, an electrically insulating separator, and an organic electrolyte solution.[1−7] The electrolyte is typically a solution of tetraethylammonium tetrafluoroborate in acetonitrile or propylene carbonate, restricting the use of EDLCs at higher operating temperatures.Ionic liquids (ILs) have received a significant degree of attention as an alternative to organic electrolytes, for EDLCs8,9 and for lithium ion batteries.[10−13] They are considered to be less hazardous than conventional electrolytes due to their nonflammable nature and the fact that they tend to exhibit negligible vapor pressures.[9,14]ILs are salts with relatively low melting temperatures (typically
Electrochemical double-layer capacitors (EDLCs) are a class of energy storage devices known for their high-power densities.[1−3] Their ability to accept or deliver charge at substantially higher rates than electrochemical cells suitable for use in applications where peak demand is substantially greater than the average load.[4,5]
We report on the behavior of neat S-Ionic liquids (ILs) in EDLCs operating at room temperature and investigate the influence that cation structure has on cell performance

Summary

Introduction

Electrochemical double-layer capacitors (EDLCs) are a class of energy storage devices known for their high-power densities (up to 10 kW kg−1).[1−3] Their ability to accept or deliver charge at substantially higher rates than electrochemical cells suitable for use in applications where peak demand is substantially greater than the average load.[4,5] Other desirable features of EDLCs are that they possess long cycle life (in excess of 500000 cycles) and relatively high energy efficiencies.[1−7] EDLCs can be used to produce systems that require less maintenance than those where energy is stored in batteries.Conventional EDLCs are comprised of activated carbonbased electrodes, an electrically insulating separator, and an organic electrolyte solution.[1−7] The electrolyte is typically a solution of tetraethylammonium tetrafluoroborate in acetonitrile or propylene carbonate, restricting the use of EDLCs at higher operating temperatures.Ionic liquids (ILs) have received a significant degree of attention as an alternative to organic electrolytes, for EDLCs8,9 and for lithium ion batteries.[10−13] They are considered to be less hazardous than conventional electrolytes due to their nonflammable nature and the fact that they tend to exhibit negligible vapor pressures.[9,14]ILs are salts with relatively low melting temperatures (typically

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