Coarse-Grained Modeling of Ion Mobility and Conductivity in Block Copolymers

Microphase separating copolymers are of interest as safe, nonflammable battery electrolytes because one microphase can solvate and allow transport of ions while the other provides mechanical strength. Motivated by the large design space of possible polymer architectures and polymer and ion chemistries, along with the need to improve ion transport properties, we study a range of related materials through generic coarse-grained simulations. The strong solvation of ions in the higher dielectric constant polymer (conducting phase) is captured using an ion-monomer potential of the same form as the interaction between an ion and an induced dipole (-S/r⁴). We also use the dielectric constant of the conducting phase to set the Coulomb interaction strength, as the large majority of ion interactions occur in that microphase. This model reproduces experimentally observed trends in lamellar domain spacing and ion conductivity versus ion concentration. We apply this model to systems with small amounts of added conducting-type homopolymer, and find that this can improve ion mobility, especially near the center of the conducting phase. Initial analysis of local and overall ion transport for systems with anions tethered to the chains will also be discussed.