Janna Maranas

Abstract:

Polymer electrolytes have potential for use in next generation lithium and sodium batteries. Replacing the liquid electrolyte currently used has several advantages: it allows use of high energy density solid lithium as the anode, removes toxic solvents, improves safety, and eliminates the need for heavy casings. Despite their advantages, the conductivity of solid polymer electrolytes is not sufficient for use in batteries. As a result, considerable effort towards improving conductivity and understanding mechanisms of lithium transport has taken place over the last 30 years. This talk considers the use of mixed anions in polymer electrolytes. In simulations on Na conducting polymer membranes, we observe that ions aggregate in linear chains when the anion contains a ring structure. When the charge localization is varied, the length of the ion chains changes. Through this type of “experiment”, we find that ion-assisted, superionic, conduction occurs when ions move quickly along the outside of the ion chain, or in hop on/hop off collective events. Both are sensitive to the ion chain length. In this artificial tuning, the ion chain length is not predictable. Further, the corresponding experimental control is lacking. Here, we present a method to control the length of ion chains using mixed anions. A strongly binding anion forms the core of the ion chain, while weakly binding anions leave cations that lead to superionic conduction. The ratio of “core” anions to “mobile” anions controls the length of ion chains, and is easily duplicated in experiments.