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Title: Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors

Abstract

Well-tailored mixtures of distinct ionic liquids can act as optimal electrolytes that extend the operating electrochemical window and improve charge storage density in supercapacitors. Here, we explore two room-temperature ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4). We study their electric double-layer behavior in the neat state and as binary mixtures on the external surfaces of onion-like carbon electrodes using quasielastic neutron scattering (QENS) and classical density functional theory techniques. Computational results reveal that a mixture with 4:1 EmimTFSI/EmimBF4 volume ratio displaces the larger [TFSI–] anions with smaller [BF4–] ions, leading to an excess adsorption of [Emim+] cations near the electrode surface. These findings are corroborated by the manifestation of nonuniform ion diffusivity change, complementing the description of structural modifications with changing composition, from QENS measurements. Molecular-level understanding of ion packing near electrodes provides insight for design of ionic liquid formulations that enhance the performance of electrochemical energy storage devices.

Authors:
ORCiD logo [1];  [2]; ORCiD logo [3]; ORCiD logo [2]; ORCiD logo [4]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of California, Riverside, CA (United States)
  3. Drexel Univ., Philadelphia, PA (United States); U.S. Naval Research Lab., Washington, D.C. (United States)
  4. Drexel Univ., Philadelphia, PA (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Energy Frontier Research Centers (EFRC) (United States). Fluid Interface Reactions, Structures and Transport Center (FIRST)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1439150
Alternate Identifier(s):
OSTI ID: 1482459
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 19; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Osti, Naresh C., Gallegos, Alejandro, Dyatkin, Boris, Wu, Jianzhong, Gogotsi, Yury, and Mamontov, Eugene. Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.8b02521.
Osti, Naresh C., Gallegos, Alejandro, Dyatkin, Boris, Wu, Jianzhong, Gogotsi, Yury, & Mamontov, Eugene. Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors. United States. https://doi.org/10.1021/acs.jpcc.8b02521
Osti, Naresh C., Gallegos, Alejandro, Dyatkin, Boris, Wu, Jianzhong, Gogotsi, Yury, and Mamontov, Eugene. Thu . "Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors". United States. https://doi.org/10.1021/acs.jpcc.8b02521. https://www.osti.gov/servlets/purl/1439150.
@article{osti_1439150,
title = {Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors},
author = {Osti, Naresh C. and Gallegos, Alejandro and Dyatkin, Boris and Wu, Jianzhong and Gogotsi, Yury and Mamontov, Eugene},
abstractNote = {Well-tailored mixtures of distinct ionic liquids can act as optimal electrolytes that extend the operating electrochemical window and improve charge storage density in supercapacitors. Here, we explore two room-temperature ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4). We study their electric double-layer behavior in the neat state and as binary mixtures on the external surfaces of onion-like carbon electrodes using quasielastic neutron scattering (QENS) and classical density functional theory techniques. Computational results reveal that a mixture with 4:1 EmimTFSI/EmimBF4 volume ratio displaces the larger [TFSI–] anions with smaller [BF4–] ions, leading to an excess adsorption of [Emim+] cations near the electrode surface. These findings are corroborated by the manifestation of nonuniform ion diffusivity change, complementing the description of structural modifications with changing composition, from QENS measurements. Molecular-level understanding of ion packing near electrodes provides insight for design of ionic liquid formulations that enhance the performance of electrochemical energy storage devices.},
doi = {10.1021/acs.jpcc.8b02521},
journal = {Journal of Physical Chemistry. C},
number = 19,
volume = 122,
place = {United States},
year = {2018},
month = {4}
}

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