Enhanced ion conduction by decoupling ion transport from polymer segmental relaxation in single-ion-conducting, polymer blend electrolytes*

The sluggish polymer segmental relaxation in solid-state polymer electrolytes (SPEs) is known to constrain conductivity enhancements and limit overall performance. Improvements in conductivity can be realized through decoupling the ion transport from polymer segmental dynamics. 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 decoupled ion transport as a function of PLiMTFSI molecular weight and ion concentration 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. This electrolyte compared favorably to the benchmark SPE – polyethylene oxide, with desirable features that could support battery operation at higher voltages using energy-dense Li metal anodes.