(723j) Ion Dynamics in Single-Ion and Salt-Doped Block Polymers Via Coarse-Grained Molecular Dynamics Simulations

Salt-doped block copolymers (BCPs) are promising solid-state battery electrolytes as they can both conduct ions through one microphase and provide mechanical robustness through the other. However, their significantly lower ion conductivity and transference number relative to standard electrolytes limits their use. Tethering the anions to the polymer backbone (creating single-ion conducting BCPs) is a possible approach to increase performance, as it allows for a transference number close to unity, though it may also impact the cation mobility. We explore the impact of tethering on ion dynamics by using coarse-grained molecular dynamics (MD) simulations. In particular, we study the effects of ion concentration and polymer dielectric constant on both salt-doped and single-ion systems. Salt-doped BCPs have lower ion conductivity than analogous single-ion BCPs, especially at lower ion concentrations. Interestingly, the local cation morphology (whether cations are paired with anions versus surrounded by monomers) is similar between the two kinds of systems, across the range values of the polymer dielectric constant studied. However, at longer length scales, the cations are more dispersed throughout the conducting domain for the single-ion systems versus the salt-doped systems. This is apparently due to the fact that the anions’ density is more evenly spread throughout the conducting domain for single-ion systems (as the anions are tethered on the conducting block). Overall, for the systems considered here, single-ion systems have an advantage in terms of cation conduction at lower ion concentrations.

This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award DE-SC0014209.