Controlling the Ion Transport Number in Solvent-in-Salt Solutions

Ivan Popov; Airat Khamzin; Ray A. Matsumoto; Wei Zhao; Xiaobo Lin; Peter T. Cummings; Alexei P. Sokolov

doi:10.1021/acs.jpcb.2c02218

Controlling the Ion Transport Number in Solvent-in-Salt Solutions

Ivan Popov, Airat Khamzin, Ray A. Matsumoto, Wei Zhao, Xiaobo Lin, Peter T. Cummings, Alexei P. Sokolov

Soft Materials and Membranes

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

7 Scopus citations

Abstract

Solvent-in-salt (SIS) systems present promising materials for the next generation of energy storage applications. The ion dynamics is significantly different in these systems from that of ionic liquids and diluted salt solutions. In this study, we analyze the ion dynamics of two salts, Li-TFSI and Li-FSI, in highly concentrated aqueous and acetonitrile solutions. We performed high-frequency dielectric measurements covering the range of up to 50 GHz and molecular dynamics simulations. The analysis of the conductivity spectra provides the characteristic crossover time between individual charge rearrangements and the normal charge diffusion regime resulting in DC conductivity. Analysis revealed that the onset of normal charge diffusion occurs at the scale of ∼1.5-3.5 Å, comparable to the average distance between the ions. Based on the idea of momentum conservation, distinct ion correlations were estimated experimentally and computationally. The analysis revealed that cation-anion correlations can be suppressed by changing the solvent concentration in SIS systems, leading to an increase of the light ion (Li⁺in our case) transport number. This discovery suggests a way for improving the light cation transport number in SIS systems by tuning the solvent concentration.

Original language	English
Pages (from-to)	4572-4583
Number of pages	12
Journal	Journal of Physical Chemistry B
Volume	126
Issue number	24
DOIs	https://doi.org/10.1021/acs.jpcb.2c02218
State	Published - Jun 23 2022

Funding

We thank Jeppe Dyre for helpful discussions. This work was supported by 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. I.P. acknowledges partial financial support by the NSF (award CHE-2102425) for the data analysis. A.Kh. is thankful to the support by the Kazan Federal University Strategic Academic Leadership Program.

Funders	Funder number
National Science Foundation	CHE-2102425
U.S. Department of Energy
Office of Science
Basic Energy Sciences
Kazan Federal University

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10.1021/acs.jpcb.2c02218

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title = "Controlling the Ion Transport Number in Solvent-in-Salt Solutions",

abstract = "Solvent-in-salt (SIS) systems present promising materials for the next generation of energy storage applications. The ion dynamics is significantly different in these systems from that of ionic liquids and diluted salt solutions. In this study, we analyze the ion dynamics of two salts, Li-TFSI and Li-FSI, in highly concentrated aqueous and acetonitrile solutions. We performed high-frequency dielectric measurements covering the range of up to 50 GHz and molecular dynamics simulations. The analysis of the conductivity spectra provides the characteristic crossover time between individual charge rearrangements and the normal charge diffusion regime resulting in DC conductivity. Analysis revealed that the onset of normal charge diffusion occurs at the scale of ∼1.5-3.5 {\AA}, comparable to the average distance between the ions. Based on the idea of momentum conservation, distinct ion correlations were estimated experimentally and computationally. The analysis revealed that cation-anion correlations can be suppressed by changing the solvent concentration in SIS systems, leading to an increase of the light ion (Li+in our case) transport number. This discovery suggests a way for improving the light cation transport number in SIS systems by tuning the solvent concentration.",

author = "Ivan Popov and Airat Khamzin and Matsumoto, {Ray A.} and Wei Zhao and Xiaobo Lin and Cummings, {Peter T.} and Sokolov, {Alexei P.}",

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AU - Popov, Ivan

AU - Khamzin, Airat

AU - Matsumoto, Ray A.

AU - Zhao, Wei

AU - Lin, Xiaobo

AU - Cummings, Peter T.

AU - Sokolov, Alexei P.

PY - 2022/6/23

Y1 - 2022/6/23

N2 - Solvent-in-salt (SIS) systems present promising materials for the next generation of energy storage applications. The ion dynamics is significantly different in these systems from that of ionic liquids and diluted salt solutions. In this study, we analyze the ion dynamics of two salts, Li-TFSI and Li-FSI, in highly concentrated aqueous and acetonitrile solutions. We performed high-frequency dielectric measurements covering the range of up to 50 GHz and molecular dynamics simulations. The analysis of the conductivity spectra provides the characteristic crossover time between individual charge rearrangements and the normal charge diffusion regime resulting in DC conductivity. Analysis revealed that the onset of normal charge diffusion occurs at the scale of ∼1.5-3.5 Å, comparable to the average distance between the ions. Based on the idea of momentum conservation, distinct ion correlations were estimated experimentally and computationally. The analysis revealed that cation-anion correlations can be suppressed by changing the solvent concentration in SIS systems, leading to an increase of the light ion (Li+in our case) transport number. This discovery suggests a way for improving the light cation transport number in SIS systems by tuning the solvent concentration.

AB - Solvent-in-salt (SIS) systems present promising materials for the next generation of energy storage applications. The ion dynamics is significantly different in these systems from that of ionic liquids and diluted salt solutions. In this study, we analyze the ion dynamics of two salts, Li-TFSI and Li-FSI, in highly concentrated aqueous and acetonitrile solutions. We performed high-frequency dielectric measurements covering the range of up to 50 GHz and molecular dynamics simulations. The analysis of the conductivity spectra provides the characteristic crossover time between individual charge rearrangements and the normal charge diffusion regime resulting in DC conductivity. Analysis revealed that the onset of normal charge diffusion occurs at the scale of ∼1.5-3.5 Å, comparable to the average distance between the ions. Based on the idea of momentum conservation, distinct ion correlations were estimated experimentally and computationally. The analysis revealed that cation-anion correlations can be suppressed by changing the solvent concentration in SIS systems, leading to an increase of the light ion (Li+in our case) transport number. This discovery suggests a way for improving the light cation transport number in SIS systems by tuning the solvent concentration.

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Controlling the Ion Transport Number in Solvent-in-Salt Solutions

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