jp8b02009_si_002.xlsx (122.19 kB)
Solution Properties and Practical Limits of Concentrated Electrolytes for Nonaqueous Redox Flow Batteries
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posted on 2018-04-05, 00:00 authored by Jingjing Zhang, R. E. Corman, Jonathon K. Schuh, Randy H. Ewoldt, Ilya A. Shkrob, Lu ZhangNonaqueous 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.
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Practical Limitsenergy density increasescharge carriers0.5 Mtarget concentrationsflow cellsROM solutionsion diffusivitiesion diffusivityclosed-shell analoguesConcentrated Electrolytesconcentration-dependent conductivityROM-containing electrolytesNRFB fluids needenergy densitysolution PropertiesSuch all-organic electrolytesNonaqueous Redox Flow Batteries Nonaqueous redox flow batterieselectrochemical stability windowsviscosityphysicochemical propertiestechno-economic analyses favor
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