Li+ Conduction in Glass-forming Single-ion Conducting Polymers with and without Ion Clusters Studied in the Impedance Frequency Regime

Single-ion conducting polymer electrolytes have been studied for their advantages such as high transference number, lower interfacial resistance with electrodes, and ability to accommodate low-cost manufacturing for battery applications. However, amorphous poly(ethylene oxide) (PEO) and related electrolytes are limited by their ion transport rate that is coupled with -EO- segmental motion. Polymer electrolytes with ion-clusters can potentially provide fast transport in ion-channels, because the ion cluster phase is ionophilic and its energy landscape is continuous. In this contribution, we report on single-ion conducting polymers with varying polymer backbone types that contain delocalized tethered anions (-sulfonyl(trifluoromethylsulfonyl)imide (-TFSI-)) prepared from side-chain monomers capable of free-radical polymerization. The polymer backbone type is found to have strong implications for ion aggregation and nanoscale morphology. The new side-chain ionic polymer with non-polar backbone (polystyrene derivative) is found to self-assemble with lamellar ordering of nanoscale ion clusters. Meanwhile, side-chain ionic polymers with polar backbones (polyacrylate and polymethacylate derivatives) were found to be less ordered and were compared to the former to generate insight on ion transport mechanisms. We show that, in the impedance frequency regime, regardless of the ion aggregation morphology that the ionic conductivity is related to α relaxation which is similar to glass-forming liquids, though with certain degrees of decoupling. Nonetheless, these results do not preclude that fast cation dynamics exist locally in the ion cluster phase.