Abstract:
Polymer electrolytes have a potential for use in next generation lithium and sodium batteries. Replacing the liquid electrolyte currently used has several advantages: it allows the 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 high ion content polymers as Na battery electrolytes. Polymer electrolytes do not conduct efficiently enough for practical application because ion motion is coupled to polymer motion. However, slow polymer motion (and thus stiffness) is critical for preventing dendrite formation that limits the use of Na or Li metal anodes. Here we demonstrate, with a combination of simulation, synthesis, and characterization, that polymer motion and ion motion decouple at high ion contents. To achieve this result, we use an anion-containing polymer with free Na cations. We design the polymer such that the ions self-assemble into chain-like aggregates. As percolation is reached, conduction remains high because stable ion chains transport free cations regardless of polymer motion.
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