Polymerized Stockmayer Fluid MD Simulation of Ion Transport in Polymeric Ionic Liquid–LiTFSI Blends

We performed polymerized Stockmayer fluid molecular dynamics simulations of the polymerized ionic liquid poly(1-ethyl-3-vinylimidazolium bis-(trifluoromethanesulfonylimide)) blended with LiTFSI at concentrations up to 5.3 M. The ionic conductivity increases markedly with salt addition, reaching an optimal polycation-to-lithium ratio of about 1:2.4 at 350 K before decreasing at higher concentrations. This enhancement, which occurs despite volumetric swelling, indicates that increased carrier population, screening-enhanced mobility, and reduced anticorrelations outweigh the dilution effect, placing the system within the polymer-in-salt regime. A Haven ratio of about 0.1 further supports this mechanism, revealing strong anticorrelated ion motion consistent with ring-like backflow in dense ionic media. We also computed orientational and translational collective dielectric constants to analyze how lithium salt addition influences these properties.