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Title: Ternary mixtures of sulfolanes and ionic liquids for use in high-temperature supercapacitors
Authors: Fletcher, Stephen
Kirkpatrick, Iain
Thring, R.H.
Dring, Roderick
Tate, Joshua L.
Geary, Harry R.M.
Black, Victoria J.
Keywords: Activated carbon
Conductivity
Eutectic
Ionic liquid
Sulfolane
Supercapacitor
Issue Date: 2018
Publisher: American Chemical Society
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.
Abstract: 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.
Description: 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.
Sponsor: This work was sponsored by the EPSRC (UK) Grant Number EP/M009394/1, “Electrochemical Vehicle Advanced Technology” (ELEVATE).
Version: Published
DOI: 10.1021/acssuschemeng.7b04117
URI: https://dspace.lboro.ac.uk/2134/32151
Publisher Link: https://doi.org/10.1021/acssuschemeng.7b04117
Appears in Collections:Published Articles (Chemistry)

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