Coarse-grained Simulations of Ion Transport in Single-ion and Salt-doped Polymer Electrolytes

Solid polymer electrolytes with a high lithium-ion transference number are of interest as they can improve charging rate, reduce ion polarization, and suppress lithium dendrite growth. This transference number, representing the fractional contribution of cations to overall conductivity, is generally low in salt-doped polymer electrolytes. In contrast, if anions are tethered to the polymer backbone to create a single-ion system, the transference number goes to one in the limit of negligible polymer motion. We use coarse-grained molecular dynamics simulations in which the only difference between salt-doped and single-ion systems is the addition of bonds tethering the anions; thus, we show a controlled comparison of the effect of tethering between systems of the same chemistry. We calculate the conductivity, transference number, and ion clustering behavior with an applied electric field in homopolymers and diblock copolymers. We will discuss effects of polymer architecture, ion concentration, and dielectric constant on ion transport in single-ion versus salt-doped polymers.