(403b) Molecular Dynamics Simulations of Single-Ion Block Copolymers: Effect of Polymer Architecture

Single-ion block copolymers are gaining interest as potential robust, nonflammable battery electrolytes with high cation transference numbers. Because all of their anions are tethered to the polymer chains, the cation transference number, the fractional contribution of cation conductivity to overall ion conductivity, is unity in the limit that transport of the polymer chains is negligible. Such a high transference number is of interest in reaching a high charging rate and avoiding concentration polarization that is possible in salt-doped systems. However, tethered anions may adversely affect polymer and cation dynamics and thus reduce cation conduction. To understand these effects, we simulate block copolymers with anions tethered at various locations on the conducting block (the block which more strongly solvates the ions), using a simple coarse-grained model. We study a variety of architectures and chemical parameters, including salt-doped systems for comparison, and analyze the ion clustering, dynamics, and mechanism of conduction. We find that tethering the anions at the ends of the chains increases the local ion concentration in the middle of the domain, yielding a density profile similar to that of salt-doped systems, but with important differences in dynamic behavior. We hope that understanding the relationships between polymer architecture and ion conduction in single-ion polymers can help guide the design of improved electrolyte materials.