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 is known to constrain conductivity enhancements and therefore limit overall performance. The decoupling of ion transport from polymer segmental dynamics is promising to break this inherent anticorrelation. In this work, we blended a glassy single-ion-conducting (SIC) polymer, poly[lithium sulfonyl(trifluoromethane sulfonyl)imide methacrylate] (PLiMTFSI), with a flexible polymer, poly(oligo-oxyethylene methyl ether methacrylate), at various compositions. We connected the ion transport mechanism to the packing efficiency of polymer chains and investigated the composition-dependent thermal and conductive properties via differential scanning calorimetry, alternating current impedance spectroscopy, and dynamic mechanical analysis. High ionic conductivities approaching 1 × 10^-2 S/cm were realized as a result of this decoupled ion transport. Additionally, immobilized TFSI^- resulted in high Li⁺ selectivity (Li⁺ transference number = 0.9), electrochemical stability (up to 4.7 V against Li⁺/Li, and limiting current density (1.8 mA/cm²), which exceeds many solvent-plasticized SIC polymer electrolytes.