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Title: Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures

Formulating room-temperature ionic liquid (RTIL) mixed electrolytes was recently proposed as an effective and convenient strategy to increase the capacitive performance of electrochemical capacitors. In this paper, we investigate the electrical double-layer (EDL) structure and the capacitance of two RTILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF 4), and their mixtures with onion-like carbon electrodes using experiment and classical density functional theory. The principal difference between these ionic liquids is the smaller diameter of the BF 4 anion relative to the TFSI anion and the EMI + cation. A volcano-shaped trend is identified for the capacitance versus the composition of the RTIL mixture. The mixture effect, which makes more counterions pack on and more co-ions leave from the electrode surface, leads to an increase of the counterion density within the EDL and thus a larger capacitance. Finally, these theoretical predictions are in good agreement with our experimental observations and offer guidance for designing RTIL mixtures for EDL supercapacitors.
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5] ;  [6] ;  [2]
  1. Univ. of California, Riverside, CA (United States). Dept. of Chemical and Environmental Engineering; East China Univ. of Science and Technology, Shanghai (China). State Key Lab. of Chemical Engineering
  2. Univ. of California, Riverside, CA (United States). Dept. of Chemical and Environmental Engineering
  3. Drexel Univ., Philadelphia, PA (United States). Dept. of Materials Science and Engineering. A.J. Drexel Nanomaterials Inst.
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
  5. East China Univ. of Science and Technology, Shanghai (China). State Key Lab. of Chemical Engineering
  6. Univ. of California, Riverside, CA (United States). Dept. of Chemistry
Publication Date:
Grant/Contract Number:
AC05-00OR22725; 91334203; 21376074; B08021
Type:
Accepted Manuscript
Journal Name:
ACS Energy Letters
Additional Journal Information:
Journal Volume: 1; Journal Issue: 1; Journal ID: ISSN 2380-8195
Publisher:
American Chemical Society (ACS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of California, Riverside, CA (United States); East China Univ. of Science and Technology, Shanghai (China)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Natural Science Foundation of China (NNSFC); Chinese Scholarship Council
Contributing Orgs:
Drexel Univ., Philadelphia, PA (United States)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1346631

Lian, C., Liu, K., Van Aken, Katherine L., Gogotsi, Yury G., Wesolowski, David J., Liu, Honglai, Jiang, D. E., and Wu, Jianzhong. Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures. United States: N. p., Web. doi:10.1021/acsenergylett.6b00010.
Lian, C., Liu, K., Van Aken, Katherine L., Gogotsi, Yury G., Wesolowski, David J., Liu, Honglai, Jiang, D. E., & Wu, Jianzhong. Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures. United States. doi:10.1021/acsenergylett.6b00010.
Lian, C., Liu, K., Van Aken, Katherine L., Gogotsi, Yury G., Wesolowski, David J., Liu, Honglai, Jiang, D. E., and Wu, Jianzhong. 2016. "Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures". United States. doi:10.1021/acsenergylett.6b00010. https://www.osti.gov/servlets/purl/1346631.
@article{osti_1346631,
title = {Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures},
author = {Lian, C. and Liu, K. and Van Aken, Katherine L. and Gogotsi, Yury G. and Wesolowski, David J. and Liu, Honglai and Jiang, D. E. and Wu, Jianzhong},
abstractNote = {Formulating room-temperature ionic liquid (RTIL) mixed electrolytes was recently proposed as an effective and convenient strategy to increase the capacitive performance of electrochemical capacitors. In this paper, we investigate the electrical double-layer (EDL) structure and the capacitance of two RTILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), and their mixtures with onion-like carbon electrodes using experiment and classical density functional theory. The principal difference between these ionic liquids is the smaller diameter of the BF4– anion relative to the TFSI– anion and the EMI+ cation. A volcano-shaped trend is identified for the capacitance versus the composition of the RTIL mixture. The mixture effect, which makes more counterions pack on and more co-ions leave from the electrode surface, leads to an increase of the counterion density within the EDL and thus a larger capacitance. Finally, these theoretical predictions are in good agreement with our experimental observations and offer guidance for designing RTIL mixtures for EDL supercapacitors.},
doi = {10.1021/acsenergylett.6b00010},
journal = {ACS Energy Letters},
number = 1,
volume = 1,
place = {United States},
year = {2016},
month = {4}
}