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General Trend of Negative Transference Number in Li Salt/Ionic Liquid Mixtures

preprint
submitted on 15.02.2019 and posted on 18.02.2019 by Nicola Molinari, Jonathan P. Mailoa, Boris Kozinsky
We show that strong cation-anion interactions in a wide range of lithium-salt/ionic liquid mixtures result in a negative lithium transference number, using molecular dynamics simulations and rigorous concentrated solution theory. This behavior fundamentally deviates from the one obtained using self-diffusion coefficient analysis and agrees well with experimental electrophoretic NMR measurements, which accounts for ion correlations. We extend these findings to several ionic liquid compositions. We investigate the degree of spatial ionic coordination employing single-linkage cluster analysis, unveiling asymmetrical anion-cation clusters. Additionally, we formulate a way to compute the effective lithium charge that corresponds to and agrees well with electrophoretic measurements and show that lithium effectively carries a negative charge in a remarkably wide range of chemistries and concentrations. The generality of our observation has significant implications for the energy storage community, emphasizing the need to reconsider the potential of these systems as next generation battery electrolytes.

History

Email Address of Submitting Author

nmolinari@seas.harvard.edu

Institution

Harvard University

Country

USA

ORCID For Submitting Author

0000-0002-2913-7030

Declaration of Conflict of Interest

Nothing to declare

Exports