Superionic Li-Ion Transport in a Single-Ion Conducting Polymer Blend Electrolyte

Single-ion conducting polymers (SICs) are promising candidates for the next generation of safer polymer electrolytes due to their stability and high transference number. However, the conductivity in SICs is often limited by the mobility of the polymer backbone as the ion mobility is coupled to segmental relaxations. We present polymer blend electrolytes, consisting of a precise single Li-ion conducting polymer with a (trifluoromethanesulfonyl)imide anion pendant group and a low molar mass poly(ethylene oxide) (PEO). Dielectric relaxation spectroscopy is used to probe both the ion transport properties and segmental dynamics of these blends, and X-ray scattering is used to evaluate their morphology. PEO associates with the ionic groups of the SIC, forming a miscible blend with pathways that promote ion transport. At a high PEO content (an ethylene oxide to Li + ratio of 10), ionic conductivities greater than 10 –5 and 10 –4 S cm –1 are achieved at 90 and 130 °C, respectively. A comparison of conductivities and polymer relaxation times shows that the high PEO content blends exhibit superionic transport, in which there is some decoupling of the Li-ion motion from the backbone mobility. This superionic transport is uncommon in single Li-ion conductors above the glass transition temperature, thus this work presents a critical step toward establishing design rules for superionic transport in SICs.