Transport anomalies in electrolytes emerging from strong ionic correlation

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. Electrolytes containing ionic liquids (ILs) possess superior chemical stability, however, poor transport properties are hindering their applicability. These systems possess high degrees of ion-ion correlation, therefore posing a non-trivial yet crucial and interesting challenge to understanding their transport properties.

Here we present molecular dynamics analysis of transport properties in IL-based electrolytes. First, we show that intra- and inter-species correlation can lead to anomalously low and even negative Li transference numbers. Second, we computationally quantify the recently measured negative Li transference number in IL-based electrolytes, and extend this surprising result to a vast range of different chemistries, suggesting a universal behavior of this class of electrolytes. Additionally, we show that lithium-containing clusters carry a negative charge. Third, we leverage our microscopic understanding to suggest and test modifications to increase the cation transference number.