Simple Route for Tuning the Morphology and Conductivity of Polymer Electrolytes: One End Functional Group is Enough

We have investigated a new means to control the morphology and conductivity of block copolymer electrolytes by the inclusion of ionic units at the chain ends. A set of poly(styrene-b-ethylene oxide) (PS-b-PEO) block copolymers having dissimilar PEO end groups (-OH, -SO3H, and -SO3Li) exhibited various self-assembled morphologies including disordered, lamellar, and hexagonal cylindrical phases. Strikingly, the addition of Li salts to PS-b-PEO with sulfonate terminal groups afforded enriched nanostructures with significant differences in their conductivities depending on the salt concentration. In particular, a gyroid morphology with a 2-fold-enhanced normalized ionic conductivity was found for the sulfonate-terminated PS-b-PEO when compared to disordered PS-b-PEO-OH. This is closely related to the structural advantages of gyroid having cocontinuous ionic channels, which enable efficient transport of Li+ ions via less tortuous ion conduction pathways. This work presents fascinating experimental insights on the enhancement of ion transport efficiencies by modulating the self-assembly nature of polymer electrolytes by substituting with a single end-functional group.