(518g) Impact of Polyether Polarity on Ionic Conductivity and Segmental Dynamics in Salt Doped Systems

Electrolytes in consumer lithium-ion batteries typically consist of mixtures of low molecular weight solvents and a lithium salt. A blending strategy enables the combination of both favorable dielectric and flow characteristics at blend compositions that maximize electrolyte performance. Polymer electrolytes are typically optimized for favorable flow characteristics as measured by low T_g and fast segmental dynamics. In this study, we explored systematic variation in the dielectric properties of polyether-based materials from both experimental and computational perspectives. Computationally in a coarse-grained model, we observed the interrelationship between dielectric constant and segmental dynamics. The ionic conductivity could be optimized with respect to the increasing dielectric constant which provided better solubilization of salt, but also increased the strength of intermolecular interactions in the system and slowed segmental dynamics. We synthesized a homologous series of polyether materials with significant variation in dielectric constant ranging from 7 to 50, which we achieved by tuning the functional group of the polyethers. Significantly, we found that at high dielectric constant the lithium salts provided a plasticizing effect on the glass transition temperature of the polymer-salt solution, and that ionic conductivity increased with salt concentration.