Polyanion Electrolytes with Well-Ordered Ionic Layers in Simulations and Experiment

We present a combined computational and experimental study, leveraging molecular dynamics simulations and X-ray scattering, to provide molecular-level insights into the layered ionic structures of polyanion electrolytes. X-ray scattering patterns for poly(ethylene oxide-co-allyl glycidyl ether-sulfonate) copolymers, P(EO-co-AGES), with various ion contents and counterions, indicated the presence of narrow lamellar morphologies. Simple bead-spring models, with polymer chain architectures very similar to the fully sulfonated poly(allyl glycidyl ether sulfonate) homopolymer (100 mol % AGES), predicted similar lamellar morphologies formed by stacked sheet-like ionic aggregates. Based on our analysis, we conclude that the ionic groups arrange into stacked layers separated by amorphous backbone layers, with the side groups partially crystallized and oriented nonparallel to the lamellae. Moreover, we propose that (i) the ionic groups are templated within the crystals to yield very stable structures up to high temperatures, and (ii) the layering is driven by the ionic interactions and not crystallization of the side chains. The cation diffusivities and ionic conductivities were severely restricted in the layered ionic morphologies of these materials.