Comparison of Ion Transport in Single-ion and Salt-doped Block Copolymers: A Coarse-grained Molecular Dynamics Study

Nanostructured block copolymers (BCPs) are of interest as solid-state electrolytes because they can allow for both ion conduction and mechanical robustness at the same time. Single-ion BCPs, with anions tethered to the conducting block of polymer backbone, have the potential to enhance the transference number and improve performance. We leverage coarse-grained molecular dynamics (MD) simulations to compare ion transport in salt-doped versus single-ion BCPs. Specifically, we calculate conductivity and transference number from simulations with an applied electric field, and focus on the effects of ion concentration and polymer dielectric constant. At low ion concentration, salt-doped systems have faster ion diffusion yet lower cation conductivity compared to analogous single-ion BCPs, while the cation conductivities are similar at high concentration. The cation conductivity difference between two types of BCPs decreases at higher dielectric constant. Thus, in the series of materials studied here, the potential advantage of single-ion systems is only relevant in situations where ionic aggregation is a concern.