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Negative effective Li transference numbers in Li salt/ionic liquid mixtures: does Li drift in the "Wrong" direction?
M Gouverneur1, F Schmidt, M Schönhoff
1Institute of Physical Chemistry, University of Muenster, Correnstraße 28/30, 48149 Münster, Germany. schoenho@uni-muenster.de.
Physical Chemistry Chemical Physics : PCCP
|March 2, 2018
Summary
Lithium ions in ionic liquids move with anions, forming charged clusters. This correlated motion impacts lithium-ion battery conductivity and transport mechanisms.
Area of Science:
- Electrochemistry
- Materials Science
- Physical Chemistry
Background:
- Ionic liquids are promising electrolytes for lithium-ion batteries.
- Understanding ion transport mechanisms is crucial for battery performance.
Purpose of the Study:
- To investigate the ion transport mechanisms in lithium salt/ionic liquid mixtures.
- To determine the effective transference numbers of lithium ions.
Main Methods:
- Utilized 1H, 19F, and 7Li electrophoretic NMR.
- Measured electrophoretic mobilities of ion species.
Main Results:
- Observed correlated motion of lithium ions with anions (TFSA- or BF4-).
- Identified negatively charged lithium-containing clusters ([Li(TFSA)2]- or [Li(BF4)3]2-).
- Determined negative effective transference numbers for lithium ions (-0.04 to -0.02).
Conclusions:
- Lithium ion transport in these ionic liquids is dominated by cluster formation and vehicular transport.
- Negative transference numbers indicate a significant contribution of anion-correlated motion to lithium transport.
- Findings have implications for optimizing lithium-ion battery electrolytes and understanding mass transport.