Electrolytes control battery recharge time and efficiency, anode/cathode stability, and ultimately safety, consequently electrolyte optimization is crucial for the design of modern energy storage device. However, conductivity and general transport properties of the cation/anion pair(s) dissolved in the electrolyte often pose a technological limitation to the viability of the battery, and progress in fundamental insights into the origin of transport limitations are challenging yet extremely valuable. We adopt theoretical and molecular modeling techniques to shine light on transport properties and correlation effects in electrolyte systems. Here we focus on two classes: polymer- and ionic liquid-based electrolytes.<br/><br/>Poly(ethylene oxide) (PEO) -based solid polymer electrolytes have a long history of research due to the easy processability and good transport properties, yet new observations that challenge our conventional understanding are still reported, especially at high salt concentrations relevant for technological applications. Our study of such regimes for PEO-Li-TFSI reveals the central role of the anion in coordinating and hindering Li-ion movements. In particular, we observe significant competition between the anion and the polymer backbone to coordinate lithium atoms and surprising formation of asymmetric cation-anion clusters. The latter observation resonates well with recent experimental findings, where negatively-charged Li-anion clusters were speculated to exist to justify the negative lithium transference number measured in this system.<br/><br/>Electrolytes containing ionic liquids (ILs) possess superior chemical stability, however, poor transport properties are hindering their applicability. Given the ionic nature, these systems possess high degrees of ion-ion correlation, therefore posing a non-trivial yet crucial and exciting challenge to understanding their transport properties. We show that, first, the strong ionic interactions result in significant correlations and deviations from ideal solution behavior. Second, we computationally confirm the recently measured negative Li transference number in Li-containing IL-based electrolytes, and extend this surprising result to a vast range of different chemistries, suggesting a universal behavior of this class of electrolytes. Third, we leverage our microscopic understanding to suggest and test modifications to increase the cation transference number.

From atomistic understanding of correlation and transport to electrolyte design

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.