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Published December 1, 2019 | Supplemental Material
Journal Article Open

Fluoride-ion solvation in non-aqueous electrolyte solutions


Understanding the factors that influence ion-solvent properties for the fluoride ion in organic solvents is key to the development of useful liquid electrolytes for fluoride-ion batteries. Using both experimental and computational methods, we examined a range of chemical and electrochemical properties for a set of organic solvents in combination with dry N,N,N-trimethylneopentylammonium fluoride (Np₁F) salt. Results showed that solvent electronic structure strongly influences Np₁F dissolution, and the pK_a of solvent protons provides a good guide to potential F⁻ reactivity. We found a number of organic solvents capable of dissolving Np₁F while providing chemically-stable F⁻ in solution and characterized three of them in detail: propionitrile (PN), 2,6-difluoropyridine (2,6-DFP), and bis(2,2,2-trifluoroethyl) ether (BTFE). Arrhenius analysis for Np₁F/PN, Np₁F/DFP, and Np₁F/BTFE electrolytes suggests that DFP facilitates the highest F⁻ ion mobility of the three neat solvents. Electrolyte mixtures of BTFE and amide co-solvents exhibit higher ionic conductivity than the neat solvents. This improved ionic conductivity is attributed to the ability of BTFE:co-solvent mixtures to partition between Np₁⁺ and F⁻ ion-aggregates, promoting better ion dissociation.

Additional Information

© 2019 The Royal Society of Chemistry and the Chinese Chemical Society. The article was received on 09 Aug 2019, accepted on 15 Oct 2019 and first published on 16 Oct 2019. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. TFM, RHG and SCJ acknowledge support from the Honda Research Institute, USA; TFM also acknowledges support from the Office of Naval Research (Award N00014-10-1-0884). VKD acknowledges support from the JPL Year Round Internship Program. SM acknowledges support from a California AGEP fellowship. This research also used resources of the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by the DOE Office of Science under contract DE-AC02-05CH11231. There are no conflicts to declare.

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