Solvent effects on Li ion transference number and dynamic ion correlations in glyme- and sulfolane-based molten Li salt solvates
The Li + transference number of electrolytes is one of the key factors contributing to the enhancement in the charge-discharge performance of Li secondary batteries. However, a design principle to achieve a high Li + transference number has not been established for liquid electrolytes. To understand...
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Published in | Physical chemistry chemical physics : PCCP Vol. 22; no. 27; pp. 15214 - 15221 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Cambridge
Royal Society of Chemistry
21.07.2020
|
Subjects | |
Online Access | Get full text |
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Summary: | The Li
+
transference number of electrolytes is one of the key factors contributing to the enhancement in the charge-discharge performance of Li secondary batteries. However, a design principle to achieve a high Li
+
transference number has not been established for liquid electrolytes. To understand the factors governing the Li
+
transference number
t
Li
, we investigated the influence of the ion-solvent interactions, Li ion coordination, and correlations of ion motions on the Li
+
transference number in glyme (G
n
,
n
= 1-4)- and sulfolane (SL)-based molten Li salt solvate electrolytes with lithium bis(trifluoromethansulfonyl)amide (LiTFSA). For the 1 : 1 tetraglyme-LiTFSA molten complex, [Li(G4)][TFSA], the Li
+
transference number estimated using the potentiostatic polarisation method (
t
PP
Li
= 0.028) was considerably lower than that estimated using the self-diffusion coefficient data with pulsed filed gradient (PFG)-NMR (
t
NMR
Li
= 0.52). The dynamic ion correlations (
i.e.
, cation-cation, anion-anion, and cation-anion cross-correlations) were determined from the experimental data on the basis of Roling and Bedrov's concentrated solution theory, and the results suggest that the strongly negative cross-correlations of the ion motions (especially for cation-cation motions) are responsible for the extremely low
t
PP
Li
of [Li(G4)][TFSA]. In contrast,
t
PP
Li
is larger than
t
NMR
Li
in the SL-based electrolytes. The high
t
PP
Li
of the SL-based electrolytes was ascribed to the substantially weaker anti-correlations of cation-cation and cation-anion motions. Whereas the translational motions of the long-lived [Li(glyme)]
+
and [TFSA]
−
dominate the ionic conduction for [Li(G4)][TFSA], Li ion hopping/exchange conduction was reported to be prevalent in the SL-based electrolytes. The unique Li ion conduction mechanism is considered to contribute to the less correlated cation-cation and cation-anion motions in SL-based electrolytes.
Ion-solvent interactions and Li ion coordination structure have a significant impact on dynamic ion correlations and Li ion transference number of molten Li salt solvate electrolytes. |
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Bibliography: | 10.1039/d0cp02181d electrode potential against the natural logarithm of the Li salt concentration in the mixture of LiTFSA in the solvents, numerical data of the six experimentally obtained parameters for the calculation of Onsager transport coefficients, and the normalised transport coefficients. See DOI Electronic supplementary information (ESI) available: Plots of the Li/Li + ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1463-9076 1463-9084 |
DOI: | 10.1039/d0cp02181d |