(410b) Parameterizing a Semi-Generic Coarse-Grained Model of a Solid Polymer Electrolyte

By applying simple, coarse-grained models to simulate solid polymer electrolytes, we can provide insight into which chemical features of the polymer and ions are most important in setting their overall behaviors. In prior work, a generic polymer and spherical ion model that included parameters to set cation and anion size, Coulomb interaction strength, and ion-monomer solvation effects via an additional 1/r⁴ interaction potential could capture and help explain trends in ion diffusivity and conductivity as a function of ion concentration. However, capturing some experimentally observed trends, such as local ion mobility within a block polymer electrolyte, has been more challenging. We expect that the different chain stiffnesses and glass transition temperatures (T_gs) of different blocks play an important role in these effects, and can be included with a limited number of additional parameters. Specifically, we consider a polymer model with additional chemical detail to map to polystyrene-block-poly(oligo-oxyethylene methyl ether methacrylate) (PS-b-POEM). We apply different bead sizes and stiff angle potentials with different equilibrium angles for each block to match each polymer type’s Kuhn length and density in the same real unit system. We also adjust self interactions of each polymer bead type to match approximate T_gs of the homopolymer systems, before adjusting the cross interactions to set an appropriate lamellar domain spacing for the diblock. We find that adding ions with solvation interactions set to reproduce the Born energy leads to a too significant increase in T_g. However, with scaled-down solvation interactions, this approach can produce a system with reasonable T_g and reduced ion mobility near the lamellar interface, as experimentally observed. We also compare the effects of increasing the ion-monomer solvation potential strength versus the ion-monomer Lennard-Jones interaction strength on T_g, transference number, and ion mobility distribution.