Rapid and highly selective ion conduction via decoupling ion transport from polymer segmental relaxation in single-ion-conducting, polymer-blend electrolytes

The inherent trade-off between rapid polymer segmental relaxation and sufficient free lithium ion (Li⁺) is known to constrain conductivity enhancement and limit performance. To break this anticorrelation, we blended a glassy single-ion-conducting polymer, poly[lithium sulfonyl(trifluoromethane sulfonyl)imide methacrylate], with a flexible ion-conducting polymer, poly(oligo-oxyethylene methyl ether methacrylate), to decouple ion transport from polymer segmental dynamics. We connected the ion transport mechanism to the packing frustration of polymer chains and investigated composition-dependent thermodynamic and conductive properties via differential scanning calorimetry, electrochemical impedance spectroscopy, and dynamic mechanical analysis. High Li⁺ conductivities (~10^-2 S/cm) with rapid transport mimicking inorganic superionic conductors were realized due to decoupled ion transport. Additionally, immobilized anion resulted in high Li⁺ selectivity (Li⁺ transference number = 0.9), electrochemical stability (4.7 V against Li⁺/Li), and limiting current density (1.8 mA/cm², electrolyte thickness = 0.05 cm). These results suggest that polymer chain packing frustration can be exploited to achieve rapid and highly selective ion conduction in high-performing polymer electrolytes.