Analyzing Ion Conductivity in Block Copolymer Electrolytes from Molecular Dynamics Simulations with an Applied Electric Field

Salt-doped block copolymers can be created with one microphase that is mechanically robust and another that solvates and conducts ions. A variety of polymer and ion types can be chosen, and molecular simulations can show how these choices impact ion motion to guide design of new materials. One strategy to increase conduction is to tune dielectric constant to reduce the degree of correlation of cation and anion motion, which can be significant in salt-doped copolymers. However, it is difficult to assess such a strategy in simulations, which often calculate self-diffusion constants of ions and estimate conductivity using the Nernst-Einstein equation (neglecting ion correlations). Conductivity can be directly calculated, including effects of correlated ion motion, from equilibrium simulations. However, this approach introduces a large statistical uncertainty. We aim to calculate conductivity from ion mobilities under an applied electric field. We ensure the field is low enough that the systems are in the linear response regime while still allowing for mobility high enough to measure accurately in the timescale of the simulation. We then compare conductivity of various systems as a function of Coulombic and polymer-ion interactions.