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Exchange-Mediated Transport in Battery Electrolytes: Ultrafast or Ultraslow?


Dereka, Bogdan; Lewis, Nicholas H C; Zhang, Yong; Hahn, Nathan T; Keim, Jonathan H; Snyder, Scott A; Maginn, Edward J; Tokmakoff, Andrei (2022). Exchange-Mediated Transport in Battery Electrolytes: Ultrafast or Ultraslow? Journal of the American Chemical Society, 144(19):8591-8604.

Abstract

Understanding the mechanisms of charge transport in batteries is important for the rational design of new electrolyte formulations. Persistent questions about ion transport mechanisms in battery electrolytes are often framed in terms of vehicular diffusion by persistent ion–solvent complexes versus structural diffusion through the breaking and reformation of ion–solvent contacts, i.e., solvent exchange events. Ultrafast two-dimensional (2D) IR spectroscopy can probe exchange processes directly via the evolution of the cross-peaks on picosecond time scales. However, vibrational energy transfer in the absence of solvent exchange gives rise to the same spectral signatures, hiding the desired processes. We employ 2D IR on solvent resonances of a mixture of acetonitrile isotopologues to differentiate chemical exchange and energy-transfer dynamics in a comprehensive series of Li+, Mg2+, Zn2+, Ca2+, and Ba2+ bis(trifluoromethylsulfonyl)imide electrolytes from the dilute to the superconcentrated regime. No exchange phenomena occur within at least 100 ps, regardless of the ion identity, salt concentration, and presence of water. All of the observed spectral dynamics originate from the intermolecular energy transfer. These results place the lower experimental boundary on the ion–solvent residence times to several hundred picoseconds, much slower than previously suggested. With the help of MD simulations and conductivity measurements on the Li+ and Zn2+ systems, we discuss these results as a continuum of vehicular and structural modalities that vary with concentration and emphasize the importance of collective electrolyte motions to ion transport. These results hold broadly applicable to many battery-relevant ions and solvents.

Abstract

Understanding the mechanisms of charge transport in batteries is important for the rational design of new electrolyte formulations. Persistent questions about ion transport mechanisms in battery electrolytes are often framed in terms of vehicular diffusion by persistent ion–solvent complexes versus structural diffusion through the breaking and reformation of ion–solvent contacts, i.e., solvent exchange events. Ultrafast two-dimensional (2D) IR spectroscopy can probe exchange processes directly via the evolution of the cross-peaks on picosecond time scales. However, vibrational energy transfer in the absence of solvent exchange gives rise to the same spectral signatures, hiding the desired processes. We employ 2D IR on solvent resonances of a mixture of acetonitrile isotopologues to differentiate chemical exchange and energy-transfer dynamics in a comprehensive series of Li+, Mg2+, Zn2+, Ca2+, and Ba2+ bis(trifluoromethylsulfonyl)imide electrolytes from the dilute to the superconcentrated regime. No exchange phenomena occur within at least 100 ps, regardless of the ion identity, salt concentration, and presence of water. All of the observed spectral dynamics originate from the intermolecular energy transfer. These results place the lower experimental boundary on the ion–solvent residence times to several hundred picoseconds, much slower than previously suggested. With the help of MD simulations and conductivity measurements on the Li+ and Zn2+ systems, we discuss these results as a continuum of vehicular and structural modalities that vary with concentration and emphasize the importance of collective electrolyte motions to ion transport. These results hold broadly applicable to many battery-relevant ions and solvents.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > Catalysis
Physical Sciences > General Chemistry
Life Sciences > Biochemistry
Physical Sciences > Colloid and Surface Chemistry
Uncontrolled Keywords:Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis
Language:English
Date:18 May 2022
Deposited On:07 Feb 2023 17:43
Last Modified:28 Jun 2024 01:39
Publisher:American Chemical Society (ACS)
ISSN:0002-7863
OA Status:Closed
Publisher DOI:https://doi.org/10.1021/jacs.2c00154
Project Information:
  • : FunderU.S. Department of Energy, Office of Science, Basic Energy Sciences
  • : Grant IDDE-SC0014305
  • : Project Title
  • : Funderwiss National Science Foundation
  • : Grant IDP400P2_180765
  • : Project Title
  • : FunderU.S. Department of Energy’s National Security Administration
  • : Grant IDDE-NA0003525
  • : Project Title