Critical Role of Anion-Solvent Interactions for Dynamics of Solvent-in-Salt Solutions

Ivan Popov; Robert L. Sacci; Nicolette C. Sanders; Ray A. Matsumoto; Matthew W. Thompson; Naresh C. Osti; Takeshi Kobayashi; Madhusudan Tyagi; Eugene Mamontov; Marek Pruski; Peter T. Cummings; Alexei P. Sokolov

doi:10.1021/acs.jpcc.9b10807

Critical Role of Anion-Solvent Interactions for Dynamics of Solvent-in-Salt Solutions

Ivan Popov, Robert L. Sacci, Nicolette C. Sanders, Ray A. Matsumoto, Matthew W. Thompson, Naresh C. Osti, Takeshi Kobayashi, Madhusudan Tyagi, Eugene Mamontov, Marek Pruski, Peter T. Cummings, Alexei P. Sokolov

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38 Scopus citations

Abstract

Most polar solvent molecules are unstable toward electrode materials used in Li-based batteries. Solid electrolytes and ionic liquids are far more stable; however, they have relatively low conductivity, and therefore electrical energy storage devices based on them would suffer from low power. Solvent-in-salt (SIS) systems combine chemical stability with relatively high conductivity. Here, we show how the nature of the employed anion affects the structure and dynamics of SIS systems. The transport of ions in lithium bis(fluorosulfonyl)imide (Li-FSI) systems was determined to be always faster than that in lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) systems. Moreover, we found that viscosity does not solely control conductivity and that the lower conductivity of TFSI^- solutions is related to their stronger interaction with the solvent. This restricts solvent dynamics and slows down ion motions compared to that of FSI^-. Interestingly, the TFSI-solvent interaction also leads to better charge separation (weaker ion-ion correlations) and a higher transference number for Li. Our results suggest that the ability to tune the solvent network formed around the anions may further improve electrolyte conductivity and Li transference number for safer and more efficient energy storage devices.

Original language	English
Pages (from-to)	8457-8466
Number of pages	10
Journal	Journal of Physical Chemistry C
Volume	124
Issue number	16
DOIs	https://doi.org/10.1021/acs.jpcc.9b10807
State	Published - Apr 23 2020

Funding

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. Research at the BASIS of the ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Access to the HFBS was provided by the Center for High Resolution Neutron Scattering, a partnership between the NIST and the NSF under agreement no. DMR-1508249. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.

Funders	Funder number
Scientific User Facilities Division
National Science Foundation	DMR-1508249
U.S. Department of Energy
National Institute of Standards and Technology
Office of Science
Basic Energy Sciences
Oak Ridge National Laboratory

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title = "Critical Role of Anion-Solvent Interactions for Dynamics of Solvent-in-Salt Solutions",

abstract = "Most polar solvent molecules are unstable toward electrode materials used in Li-based batteries. Solid electrolytes and ionic liquids are far more stable; however, they have relatively low conductivity, and therefore electrical energy storage devices based on them would suffer from low power. Solvent-in-salt (SIS) systems combine chemical stability with relatively high conductivity. Here, we show how the nature of the employed anion affects the structure and dynamics of SIS systems. The transport of ions in lithium bis(fluorosulfonyl)imide (Li-FSI) systems was determined to be always faster than that in lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) systems. Moreover, we found that viscosity does not solely control conductivity and that the lower conductivity of TFSI- solutions is related to their stronger interaction with the solvent. This restricts solvent dynamics and slows down ion motions compared to that of FSI-. Interestingly, the TFSI-solvent interaction also leads to better charge separation (weaker ion-ion correlations) and a higher transference number for Li. Our results suggest that the ability to tune the solvent network formed around the anions may further improve electrolyte conductivity and Li transference number for safer and more efficient energy storage devices.",

author = "Ivan Popov and Sacci, {Robert L.} and Sanders, {Nicolette C.} and Matsumoto, {Ray A.} and Thompson, {Matthew W.} and Osti, {Naresh C.} and Takeshi Kobayashi and Madhusudan Tyagi and Eugene Mamontov and Marek Pruski and Cummings, {Peter T.} and Sokolov, {Alexei P.}",

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AU - Sacci, Robert L.

AU - Sanders, Nicolette C.

AU - Matsumoto, Ray A.

AU - Thompson, Matthew W.

AU - Osti, Naresh C.

AU - Kobayashi, Takeshi

AU - Tyagi, Madhusudan

AU - Mamontov, Eugene

AU - Pruski, Marek

AU - Cummings, Peter T.

AU - Sokolov, Alexei P.

PY - 2020/4/23

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N2 - Most polar solvent molecules are unstable toward electrode materials used in Li-based batteries. Solid electrolytes and ionic liquids are far more stable; however, they have relatively low conductivity, and therefore electrical energy storage devices based on them would suffer from low power. Solvent-in-salt (SIS) systems combine chemical stability with relatively high conductivity. Here, we show how the nature of the employed anion affects the structure and dynamics of SIS systems. The transport of ions in lithium bis(fluorosulfonyl)imide (Li-FSI) systems was determined to be always faster than that in lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) systems. Moreover, we found that viscosity does not solely control conductivity and that the lower conductivity of TFSI- solutions is related to their stronger interaction with the solvent. This restricts solvent dynamics and slows down ion motions compared to that of FSI-. Interestingly, the TFSI-solvent interaction also leads to better charge separation (weaker ion-ion correlations) and a higher transference number for Li. Our results suggest that the ability to tune the solvent network formed around the anions may further improve electrolyte conductivity and Li transference number for safer and more efficient energy storage devices.

AB - Most polar solvent molecules are unstable toward electrode materials used in Li-based batteries. Solid electrolytes and ionic liquids are far more stable; however, they have relatively low conductivity, and therefore electrical energy storage devices based on them would suffer from low power. Solvent-in-salt (SIS) systems combine chemical stability with relatively high conductivity. Here, we show how the nature of the employed anion affects the structure and dynamics of SIS systems. The transport of ions in lithium bis(fluorosulfonyl)imide (Li-FSI) systems was determined to be always faster than that in lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) systems. Moreover, we found that viscosity does not solely control conductivity and that the lower conductivity of TFSI- solutions is related to their stronger interaction with the solvent. This restricts solvent dynamics and slows down ion motions compared to that of FSI-. Interestingly, the TFSI-solvent interaction also leads to better charge separation (weaker ion-ion correlations) and a higher transference number for Li. Our results suggest that the ability to tune the solvent network formed around the anions may further improve electrolyte conductivity and Li transference number for safer and more efficient energy storage devices.

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Critical Role of Anion-Solvent Interactions for Dynamics of Solvent-in-Salt Solutions

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