Ionic Conductivity of Highly-Asymmetric Block Copolymers Based on Polymer Ionic Liquids

Block copolymers (BCPs) based on nonionic polymers linked to polymer ionic liquids (PILs) are a promising class of electrolytes for energy storage and conversion devices. Our prior studies found that the bulk ionic conductivity of certain lamellar-forming materials was significantly depressed relative to simple predictions of the normalized ionic conductivity based on the ionic conductivity of the PIL homopolymer, the composition of the BCP, and the self-assembled morphology of the BCP. We hypothesized that this depression is due to poor connectivity among ionic domains in the lamellar phase, and we tested this hypothesis by examining the ionic conductivity in a series of highly asymmetric BCPs (spherical and cylindrical morphologies) having a majority PIL phase. We found that the normalized ionic conductivity in these materials met or exceeded the predicted values. Notably, the ionic conductivity of some highly asymmetric BCPs exceeded that of the homopolymer PIL, an effect that is tentatively attributed to enhanced decoupling of ion transport and segmental dynamics in the confined BCP domain.