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Effect of High Salt Concentration on Ion Clustering and Transport in Polymer Solid Electrolytes: a Molecular Dynamics Study of PEO-LiTFSI

preprint
submitted on 21.05.2018 and posted on 22.05.2018 by Nicola Molinari, Jonathan P. Mailoa, Boris Kozinsky

The model and analysis methods developed in this work are generally applicable to any polymer electrolyte/cation-anion combination, but we focus on the currently most prominent polymer electrolyte material system: poly(ethylene) oxide/Li- bis(trifluoromethane) sulfonamide (PEO + LiTFSI). The obtained results are surprising and challenge the conventional understanding of ionic transport in polymer electrolytes: the investigation of a technologically relevant salt concentration range (1 - 4 M) revealed the central role of the anion in coordinating and hindering Li ion movement. Our results provide insights into correlated ion dynamics, at the same time enabling rational design of better PEO-based electrolytes. In particular, we report the following novel observations. 1. Strong binding of the Li cation with the polymer competes with significant correlation of the cation with the salt anion. 2. The appearance of cation-anion clusters, especially at high concentration. 3. The asymmetry in the composition (and therefore charge) of such clusters; specifically, we find the tendency for clusters to have a higher number of anions than cations.

History

Email Address of Submitting Author

nicola.molinari12@alumni.imperial.ac.uk

Email Address(es) for Other Author(s)

jonathan.mailoa@us.bosch.com bkoz@seas.harvard.edu

Institution

Robert Bosch LLC, Imperial College London, Harvard University

Country

United States of America

ORCID For Submitting Author

0000-0002-2913-7030

Declaration of Conflict of Interest

No conflict of Interest

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