Ion States Impact Charge Transport and Dielectric Constant for Poly(ethylene oxide)-Based Sulfonylimide Lithium Ionomers

Understanding dielectric response and charge transport in ion-containing polymers is essential for the design and implementation of these materials in energy-related applications. Our previous study identified the significant impacts of anion chemical composition on ion conduction for poly(ethylene oxide)-based lithium ionomers with polymer-fixed sulfonylimide (MTLi) and sulfonate anions (J. Mater. Chem. C, 2022, 10, 14569). In this study, we further explore the dielectric response and Li⁺ conduction in the context of different ion states using DFT. The most relevant ion states impacting the dielectric response and Li⁺ conduction are represented with a four-state model. DFT calculation using the cluster-continuum solvation model captures the local solvation effects of poly(ethylene oxide) and reveals low cluster dissociation energy between neutral and charged states. Low cluster dissociation energy explains the weakly aggregated morphology with low aggregation number based on X-ray scattering and implies that Li⁺ rapidly exchanges between different ion states. Consequently, Li⁺ can hop along aggregates for high ion content MTLi, which results in its significant dielectric response, comparable conductivity, and lower Haven ratio despite stronger aggregation than the low ion content counterparts. Different from typical ionomers where raising ion content is detrimental to the ion transport and dielectric response, the understandings based on different ion states for MTLi offer new insights to promote ion conduction and dielectric response for single-ion conducting ionomers.