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

Journal Article · · Journal of Physical Chemistry. C
 [1];  [1];  [1];  [2];  [2];  [1];  [3];  [4];  [1];  [3];  [2];  [5]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Vanderbilt Univ., Nashville, TN (United States)
  3. Ames Lab., and Iowa State Univ., Ames, IA (United States)
  4. National Inst. of Standards and Technology, Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
+ Show Author Affiliations
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. Finally, 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.
Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
National Institute of Standards and Technology (NIST); National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1616800
Journal Information:
Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 16 Vol. 124; ISSN 1932-7447
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
diffusion
electrical conductivity
salts
solution chemistry
solvents