Influence of anion chemistry on ion transport in single ion conducting polymer electrolytes

Single ion conducting (SIC) polymer electrolytes exhibit highly selective lithium ion conduction, crucial for eliminating safety issues in lithium-ion batteries. In this work, we report results from atomistic molecular dynamics simulations focused on elucidating the influence of different anion chemistries on ionic conductivity in SIC copolymer electrolytes. For these electrolyte systems (synthesized by our experimental collaborators), the polymer backbone was anchored with polyethylene glycol (PEG) chains and lithiated anionic moieties. We consider derivatives of three different anions: acrylic acid, Acrylamido methylpropane sulfonic acid (AMPS), and bis(trifluoromethane)sulfonamide (TFSI). Our results suggest that with increasing anion content, the Li⁺ transport mechanism transitions from vehicular, in which Li⁺ diffuses together with the polyanion, to a combination of hopping and rearrangement of neighboring ion clusters. At a fixed anion content, the ion-polymer coordination behavior and the ion cluster morphologies are observed to be significantly different for the different anion chemistries considered in this study, thus rationalizing the significant influence of anion choice on the observed transport characteristics.