Asymmetric Composition of Ionic Aggregates and the Origin of High Correlated Transference Number in Water-in-Salt Electrolytes

Yu, Zhou; Curtiss, Larry A.; Winans, Randall E.; Zhang, Yang; Li, Tao; Cheng, Lei

doi:10.1021/acs.jpclett.9b03495

Title: Asymmetric Composition of Ionic Aggregates and the Origin of High Correlated Transference Number in Water-in-Salt Electrolytes

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Abstract

"Water-in-salt" electrolytes open up exciting new avenues for expanding the electrochemical window of aqueous electrolytes. We investigated the solvation structure and dynamics of highly concentrated lithium bis(trifluoromethane)sulfonimide aqueous electrolyte using experimentally corroborated molecular dynamics simulations. The simulations revealed that the heterogeneous structure of the electrolyte comprises percolating networks of ion and water domains/aggregates. Interestingly, the ionic regions are composed of more TFSI^- ions than Li⁺ ions. The Li⁺-ion transport mechanism was further explored. Li⁺ ions can hop along the coordinated TFSI- ions in the ionic aggregates. The calculated correlated transference number of the 20 m electrolyte is similar to 0.32, which is reasonably high for the high concentration due to a weak negative correlation between the motion of cations and anions within the heterogeneous microscopic domains. These molecular dynamics results connect the heterogeneous structure of the electrolyte to the correlated dynamics of the Li⁺ ion and provide a new understanding of the Li⁺-ion transport mechanism in this novel electrolyte.

Authors:

^[1];

^[2];

^[3]; Li, Tao ^[4];

^[1]

Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division and Joint Center for Energy Storage Research
Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science Division
Univ. of Illinois at Urbana-Champaign, IL (United States). Dept. of Nuclear, Plasma, and Radiological Engineering, Beckman Inst. for Advanced Science and Technology, Program of Computational Science and Engineering and Dept. of Electrical and Computer Engineering
Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science Division; Northern Illinois Univ., DeKalb, IL (United States). Dept. of Chemistry and Biochemistry

Publication Date:: Fri Jan 17 00:00:00 EST 2020

Research Org.:: Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:: USDOE Office of Science - Office of Basic Energy Sciences - Joint Center for Energy Storage Research (JCESR)

OSTI Identifier:: 1605988

Grant/Contract Number:: AC02-06CH11357

Resource Type:: Accepted Manuscript

Journal Name:: Journal of Physical Chemistry Letters

Additional Journal Information:: Journal Volume: 11; Journal Issue: 4; Journal ID: ISSN 1948-7185

Publisher:: American Chemical Society

Country of Publication:: United States

Language:: English

Subject:: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; correlated transference number; ionic aggregate; molecular dynamics; water-in-salt electrolytes

Citation Formats


                    Yu, Zhou, Curtiss, Larry A., Winans, Randall E., Zhang, Yang, Li, Tao, and Cheng, Lei. Asymmetric Composition of Ionic Aggregates and the Origin of High Correlated Transference Number in Water-in-Salt Electrolytes.  United States: N. p., 2020. 
Web.  doi:10.1021/acs.jpclett.9b03495.

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                    Yu, Zhou, Curtiss, Larry A., Winans, Randall E., Zhang, Yang, Li, Tao, & Cheng, Lei. Asymmetric Composition of Ionic Aggregates and the Origin of High Correlated Transference Number in Water-in-Salt Electrolytes.  United States.  https://doi.org/10.1021/acs.jpclett.9b03495

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                    Yu, Zhou, Curtiss, Larry A., Winans, Randall E., Zhang, Yang, Li, Tao, and Cheng, Lei. Fri .  
"Asymmetric Composition of Ionic Aggregates and the Origin of High Correlated Transference Number in Water-in-Salt Electrolytes".  United States.  https://doi.org/10.1021/acs.jpclett.9b03495.  https://www.osti.gov/servlets/purl/1605988.

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@article{osti_1605988,

  title        = {Asymmetric Composition of Ionic Aggregates and the Origin of High Correlated Transference Number in Water-in-Salt Electrolytes},

  author       = {Yu, Zhou and Curtiss, Larry A. and Winans, Randall E. and Zhang, Yang and Li, Tao and Cheng, Lei},

  abstractNote = {"Water-in-salt" electrolytes open up exciting new avenues for expanding the electrochemical window of aqueous electrolytes. We investigated the solvation structure and dynamics of highly concentrated lithium bis(trifluoromethane)sulfonimide aqueous electrolyte using experimentally corroborated molecular dynamics simulations. The simulations revealed that the heterogeneous structure of the electrolyte comprises percolating networks of ion and water domains/aggregates. Interestingly, the ionic regions are composed of more TFSI- ions than Li+ ions. The Li+-ion transport mechanism was further explored. Li+ ions can hop along the coordinated TFSI- ions in the ionic aggregates. The calculated correlated transference number of the 20 m electrolyte is similar to 0.32, which is reasonably high for the high concentration due to a weak negative correlation between the motion of cations and anions within the heterogeneous microscopic domains. These molecular dynamics results connect the heterogeneous structure of the electrolyte to the correlated dynamics of the Li+ ion and provide a new understanding of the Li+-ion transport mechanism in this novel electrolyte.},

  doi          = {10.1021/acs.jpclett.9b03495},

  journal      = {Journal of Physical Chemistry Letters},

  number       = 4,

  volume       = 11,

  place        = {United States},

  year         = {Fri Jan 17 00:00:00 EST 2020},

  month        = {Fri Jan 17 00:00:00 EST 2020}

}

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