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Ternary mixtures of sulfolanes and ionic liquids for use in high-temperature supercapacitors

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posted on 08.03.2018 by Stephen Fletcher, Iain Kirkpatrick, Rob Thring, Rod Dring, Joshua L. Tate, Harry R.M. Geary, Victoria J. Black
Ionic liquids are a natural choice for supercapacitor electrolytes. However, their cost is currently high. In the present work, we report the use of ternary mixtures of sulfolane, 3-methyl sulfolane, and quaternary ammonium salts (quats) as low-cost alternatives. Sulfolane was chosen because it has a high Hildebrand solubility parameter (δ H = 27.2 MPa 1/2 ) and an exceptionally high dipole moment (μ = 4.7 D), which means that it mixes readily with ionic liquids. It also has a high flash point (165 °C), a high boiling point (285 °C), and a wide two-electrode (full-cell) voltage stability window ( > 7 V). The only problem is its high freezing point (27 °C). However, by using a eutectic mixture of sulfolane with 3-methyl sulfolane, we could depress the freezing point to -17 °C. A second goal of the present work was to increase the electrical conductivity of the electrolyte beyond its present-day value of 2.1 mS cm -1 at 25 °C, currently provided by butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (BTM-TFSI). We explored two methods of doing this: (1) mixing the ionic liquid with the sulfolane eutectic and (2) replacing the low-mobility TFSI anion with the high-mobility MTC anion (methanetricarbonitrile). At the optimum composition, the conductivity reached 12.2 mS cm -1 at 25 °C.

Funding

This work was sponsored by the EPSRC (UK) Grant Number EP/M009394/1, “Electrochemical Vehicle Advanced Technology” (ELEVATE).

History

School

  • Science

Department

  • Chemistry

Published in

ACS Sustainable Chemistry and Engineering

Volume

6

Issue

2

Pages

2612 - 2620

Citation

FLETCHER, S. ... et al., 2018. Ternary mixtures of sulfolanes and ionic liquids for use in high-temperature supercapacitors. ACS Sustainable Chemistry and Engineering, 6 (2), pp. 2612 - 2620.

Publisher

American Chemical Society

Version

VoR (Version of Record)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution 4.0 International (CC BY 4.0) licence. Full details of this licence are available at: http://creativecommons.org/licenses/ by/4.0/

Acceptance date

06/12/2017

Publication date

2018

Notes

ACS AuthorChoice - This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.

eISSN

2168-0485

Language

en

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