Solution Properties and Practical Limits of Concentrated Electrolytes for Nonaqueous Redox Flow Batteries

Jingjing Zhang, R. E. Corman, Jonathon K. Schuh, Randy H Ewoldt, Ilya A. Shkrob, Lu Zhang

Research output: Contribution to journalArticle

Abstract

Nonaqueous redox flow batteries (NRFBs) use energized organic fluids that contain redox active organic molecules (ROMs) and supporting electrolyte. Such all-organic electrolytes have wider electrochemical stability windows than the more familiar aqueous electrolytes, potentially allowing a higher energy density in the solutions of charged ROMs. As this energy density increases linearly with the concentration of the charge carriers, physicochemical properties of concentrated ROM solutions in both states of charge present considerable practical interest. For NRFBs to become competitive with other types of flow cells, the current techno-economic analyses favor highly concentrated solutions (>1 M) with high ionic conductivity (>5 mS/cm). It is not presently clear that such solutions can have the required dynamic properties. In this study, we show that ion diffusivities and conductivities of ROM-containing electrolytes reach maxima around 0.5 M and decrease significantly at higher concentrations; realistic limits are established for variations of these parameters. Furthermore, using closed-shell analogues for open-shell charged ROMs, we show that reconstitution of highly concentrated fluids during electrochemical charging will have strong adverse effects on their properties, including an increase in viscosity and decrease in conductivity and ion diffusivity. Given our results, it appears that the target concentrations of NRFB fluids need to be reconsidered in terms of concentration-dependent conductivity and viscosity.

Original languageEnglish (US)
Pages (from-to)8159-8172
Number of pages14
JournalJournal of Physical Chemistry C
Volume122
Issue number15
DOIs
StatePublished - Apr 19 2018

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Electrolytes
electric batteries
electrolytes
Molecules
Fluids
Viscosity
Ions
molecules
conductivity
diffusivity
fluids
Ionic conductivity
Charge carriers
flux density
viscosity
Oxidation-Reduction
Flow batteries
Economics
dynamic characteristics
ion currents

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Solution Properties and Practical Limits of Concentrated Electrolytes for Nonaqueous Redox Flow Batteries. / Zhang, Jingjing; Corman, R. E.; Schuh, Jonathon K.; Ewoldt, Randy H; Shkrob, Ilya A.; Zhang, Lu.

In: Journal of Physical Chemistry C, Vol. 122, No. 15, 19.04.2018, p. 8159-8172.

Research output: Contribution to journalArticle

Zhang, Jingjing ; Corman, R. E. ; Schuh, Jonathon K. ; Ewoldt, Randy H ; Shkrob, Ilya A. ; Zhang, Lu. / Solution Properties and Practical Limits of Concentrated Electrolytes for Nonaqueous Redox Flow Batteries. In: Journal of Physical Chemistry C. 2018 ; Vol. 122, No. 15. pp. 8159-8172.
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