Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors

Naresh C. Osti; Alejandro Gallegos; Boris Dyatkin; Jianzhong Wu; Yury Gogotsi; Eugene Mamontov

doi:10.1021/acs.jpcc.8b02521

Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors

Naresh C. Osti, Alejandro Gallegos, Boris Dyatkin, Jianzhong Wu, Yury Gogotsi, Eugene Mamontov

Chemical Spectroscopy

Research output: Contribution to journal › Article › peer-review

57 Scopus citations

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.

Original language	English
Pages (from-to)	10476-10481
Number of pages	6
Journal	Journal of Physical Chemistry C
Volume	122
Issue number	19
DOIs	https://doi.org/10.1021/acs.jpcc.8b02521
State	Published - May 17 2018

Funding

This work was supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Work at ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for U.S. DOE under contract no. DEAC05-00OR22725. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under contract no. DE-AC02-05CH11231.

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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.",

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AU - Gogotsi, Yury

AU - Mamontov, Eugene

PY - 2018/5/17

Y1 - 2018/5/17

N2 - 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.

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Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors

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