Effect of Host Incompatibility and Polarity Contrast on Ion Transport in Ternary Polymer-Polymer-Salt Blend Electrolytes

Abstract

We study ternary polymer-polymer-salt blend electrolytes using coarsegrained molecular dynamics. We specifically examine the influence of the polymer hosts' incompatibility and polarity contrast on electrolyte ion transport characteristics. We find that, at moderate-to high-polarity contrasts, improving the miscibility of the polymer hosts by reducing their inherent incompatibility improves ionic transport, as measured by the ionic conductivity. However, contrary to expectations, ionic conduction slows with increased miscibility in low-polarity contrast electrolytes. Upon examining the underlying material properties, we find that ionic aggregation exhibits trends similar to ionic conductivity and is thus likely the controlling factor in these polymer-blend electrolytes. Our results suggest that ionic conduction can be improved in real polymer electrolytes by choosing chemistries that promote simultaneous miscibility and polarity contrast between the polymer hosts.

Molecular Dynamics Simulations of Ion-Containing Polymers Using Generic Coarse-Grained Models

“…The improved conductivity was attributed to both better local ion solvation (less ionic aggregation) by the high-polarity polymers as well as faster system dynamics of the low-polarity polymers which were excluded from interacting with ions. 154 More recently, they employed a Bayesian optimization method with the same CG framework to understand how one can simultaneously maximize the transport and mechanical properties of polymer blend electrolytes. In short, a trade-off between ion conductivity and viscosity in such systems was found.…”

Relationship between Ionic Conductivity, Glass Transition Temperature, and Dielectric Constant in Poly(vinyl ether) Lithium Electrolytes

“…The study of the mechanism and structure–property relationships for ionic conductivity remains a contemporary research topic. While a generally accepted perspective is that a low glass-transition temperature ( T g ) with accompanying low viscosity is prerequisite, the importance of the polarity of the polymer host is gaining recognition. − The solubility of lithium salts and their associated states in low polarity polymers has been explored in earlier studies by Stevens and Jacobsson using lithium perchlorate and lithium triflate dissolved in poly­(propylene oxide) (PPO) at low molecular weights (400 and 4000 g/mol) . Hall and co-workers have computationally probed how ion solvation, salt concentration, polymer molecular weight, and other factors affect the movement of ions through polymers. − They suggest that stronger ion–ion interactions lower overall conductivity and that increasing salt concentration can increase or decrease conductivity depending on ion solvation.…”

“…In our recent work, we have investigated the influence of both segmental dynamics and polarity of the host polymer on ion-transport in single-polymer and blend polymer electrolytes using molecular dynamics simulations. − Two regimes were identified for single-polymer electrolytes: At low polarity, ion-transport in the system was limited by ion dissociation into the polymer medium and ionic conductivity increased with polymer polarity . At higher polarity, stronger polymer–polymer and polymer–ion interactions slow polymer segmental dynamics, which reduced further increases in ionic conductivity with increases in polarity.…”

Ion Conductivity and Correlations in Model Salt-Doped Polymers: Effects of Interaction Strength and Concentration

“…Unphysical overall Λ/Λ N E values larger than 1.0 were sometimes encountered, apparently due to the poor statistics. 28,29,32,33 Several methods have been used to reduce statistical noise in the conductivity calculation such as 1) using only the short-time scale data to allow for significant averaging and because the collective ion migration terms tend to fluctuate wildly at long time scales, 7,[27][28][29]32,33 2) considering ion clusters as noninteracting charge carriers and applying the Nernst-Einstein equation with the diffusion constants and net charges of the different types of ion clusters, 34 and 3) measuring ion mobility from nonequilibrium simulations with an external electric field. 31,[35][36][37][38] Prior studies have compared conductivities estimated by different methods for several specific systems.…”