The Importance of Morphology on Ion Transport in Single-Ion, Comb-Branched Copolymer Electrolytes: Experiments and Simulations

Single-ion conducting polymer electrolytes (SICPEs) offer high lithium transference numbers and desirable physical properties while maintaining moderate conductivities. Bottlebrush and comb-branched copolymer electrolytes are a particular architecture that offer modularity and increased ion solvation. Despite this promise, the ion transport in these systems is poorly understood. In this report, we investigated lithium-ion transport in comb-branched SICPEs using a combination of experiments and atomistic simulations. A series of solvent-free SICPEs were synthesized by copolymerization of poly(ethylene glycol) methyl ether acrylate (PEGMEA) with varying lithiated anionic groups in different ratios of the ionic species to the PEG side chain. Poly(Lithium 3-[(trifluoromethane) sulfonamidosulfonyl]propyl methacrylate-co-poly(ethylene glycol methyl ether acrylate)) (p(MPTFSI-co-PEGMEA) exhibited both highest ionic conductivity (on the order of 10–5 S/cm at room temperature) and degree of decoupling of ionic conductivity from polymer segmental dynamics. Simulations revealed that in electrolytes with low ion concentrations, Li+ transport occurs through the vehicular codiffusion of lithium ions and the polyanions. In contrast, for higher anion compositions, the primary mechanism of Li+ transport is through Li+ ion hopping among the percolated ionic aggregates. Finally, we demonstrate that the behavior of ion hopping is influenced in a nonintuitive manner by the ion cluster morphology based on SICPE anion identity.