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Fourteen kinds of ammonium salt, including nine ionic liquids, were evaluated for use as the electrolyte (as a solute) of an electric double layer capacitor (EDLC) from the viewpoint of practical performance and thermal stability. For this study, three kinds of anion species were selected for the counter anion: tetrafluoroborate (BF4), hexafluorophosphate (PF6) and bis(trifluoromethylsulfonyl)imide (TFSI) anions. A series of EDLCs with only 0.4% deviation in the capacitance of each cell, based on activated carbon and various salts in propylene carbonate (PC), were strictly prepared. The capacitance at room temperature, and the resistance value of the EDLCs at a relatively large direct current at low temperatures were measured. We also examined the durability of these systems by continuous charging at 70 °C and 3.0 V. We report that N-(2-methoxyethyl)-N-methylpyrrolidinium-BF4, a cyclic aliphatic quaternary ammonium with a methoxyethyl functional group, is the preferred ionic liquid for an EDLC electrolyte with respect to capacitance, power density, even at low temperatures and thermal durability.

© The Electrochemical Society, Inc. 2005. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproducted, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in JOURNAL OF THE ELECTROCHEMICAL SOCIETY 152 (4): A710-A715 2005., Article, Journal of the Electrochemical Society. 152(4):A710-A715 (2005)

An aliphatic quaternary ammonium salt which has a methoxyethyl group on the nitrogen atom formed an ionic liquid (room temperature molten salt) when combined with the tetrafluoroborate (BF 4 − ) and bis(trifluoromethylsulfonyl)imide [TFSI; (CF 3 SO 2 ) 2 N − ] anions. The limiting oxidation and reduction potentials, specific conductivity, and some other physicochemical properties of the novel ionic liquids, N , N -diethyl- N -methyl- N -(2-methoxyethyl)ammonium tetrafluoroborate (DEME-BF 4 ) and DEME-TFSI have been evaluated and compared with those of 1-ethyl-3-methylimidazolium tetrafluoroborate. DEME-BF 4 is a practically useful ionic liquid for electrochemical capacitors as it has a quite wide potential window (6.0 V) and high ionic conductivity (4.8 mS cm −1 at 25 °C). We prepared an electric double layer capacitor (EDLC) composed of a pair of activated carbon electrodes and DEME-BF 4 as the electrolyte. This EDLC (working voltage ∼2.5 V) has both, a higher capacity above room temperature and a better charge–discharge cycle durability at 100 °C when compared to a conventional EDLC using an organic liquid electrolyte such as a tetraethylammonium tetrafluoroborate in propylene carbonate.

A simple and very efficient synthesis of N-tosylindole is described, based on the acid-catalysed cyclization of ortho-alkylated N-tosylanilides, which can be prepared from aniline and dialkyl sulfide by [2,3]sigmatropic rearrangements