Seeing the Unseen: Mg 2+ , Na + , and K + Transference Numbers in Post-Li Battery Electrolytes by Electrophoretic Nuclear Magnetic Resonance
The growing demand for energy storage devices worldwide combined with limited resources for lithium attracts interest in other alkali or alkaline earth metals. In addition to conductivity, the cation transference number is a decisive parameter to rank the electrolyte performance. However, the existi...
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Veröffentlicht in: | Journal of the American Chemical Society 2024-04, Vol.146 (16), p.11105 |
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Hauptverfasser: | , , , , |
Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | The growing demand for energy storage devices worldwide combined with limited resources for lithium attracts interest in other alkali or alkaline earth metals. In addition to conductivity, the cation transference number
is a decisive parameter to rank the electrolyte performance. However, the existing experimental methods for its determination suffer from various intrinsic problems. We demonstrate here a novel approach for
determination based on determining the total conductivity with impedance spectroscopy (IS) and the partial conductivity of the anion species, with the latter being obtained from the anion mobility by electrophoretic NMR. First, this eNMR/IS approach is validated by comparing
values from different methods in a Li-based solvate ionic liquid electrolyte. Then, it is applied to obtain
of cations with nuclei not detectable in NMR transport measurements, employing bis(trifluoromethanesulfonyl)imide (TFSI)-based metal salts. Solvate ionic liquids consisting of triethylene glycol dimethyl ether (G3) and Mg(TFSI)
or NaTFSI yield values of
and
on the order of 0.4, similar to
. Furthermore, we apply the method to polymer electrolytes, again testing the concept with LiTFSI, and finally investigating NaTFSI, KTFSI, and Mg(TFSI)
in poly(ethylene oxide). Values of
and
are in the range of 0.14-0.2, similar to those of
, while Mg
shows a higher transference number (
= 0.3). The method is very versatile as it allows quantification of
for any type of cation, and moreover, it is applicable to highly concentrated electrolytes without suffering from assumptions about dissociation or from unknown interfacial resistances which impede electrochemical methods. |
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ISSN: | 0002-7863 1520-5126 1520-5126 |
DOI: | 10.1021/jacs.3c12272 |