Relationship between Ion Dissociation, Melt Morphology, and Electrochemical Performance of Lithium and Magnesium Single-Ion Conducting Block Copolymers

Single-ion conducting block copolymers, such as poly(ethylene oxide)-b-poly[(styrene-4-sulfonyltrifluoromethylsulfonyl)imide lithium] (PEO–P[(STFSI)Li]), represent an exciting new class of materials capable of improving the performance of solid-state batteries with metal anodes. In this work, we report on the synthesis and characterization of a matched set of lithiated (PEO–P[(STFSI)Li]) and magnesiated (PEO–P[(STFSI)2Mg]) single-ion conducting diblock copolymers. We measure the temperature dependence of ionic conductivity, and through analysis using the Vogel–Tamman–Fulcher (VTF) relation, demonstrate that ion dissociation is significantly lower for all PEO–P[(STFSI)2Mg] samples when compared to their PEO–P[(STFSI)Li] counterparts. The VTF parameter characterizing the activation barrier to ion hopping was similar for both cations, but the VTF prefactor that reflects effective charge carrier concentration was higher in the lithiated samples by an order of magnitude. We study the melt morphology of the sin...