Mixed Ionic Liquid Improves Electrolyte Dynamics in Supercapacitors
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Univ. of California, Riverside, CA (United States)
- Drexel Univ., Philadelphia, PA (United States); U.S. Naval Research Lab., Washington, D.C. (United States)
- Drexel Univ., Philadelphia, PA (United States)
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.
- Research Organization:
- 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 Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1439150
- Alternate ID(s):
- OSTI ID: 1482459
- Journal Information:
- Journal of Physical Chemistry. C, Vol. 122, Issue 19; ISSN 1932-7447
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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