Coarse-grained molecular dynamics simulations to study effect of cation charge density in polymer electrolytes

Due to the relatively low abundance of lithium as well as safety concerns, there has been renewed interest recently in batteries designed with alternative cations, including other monovalent ions as well as divalent ions such as zinc and magnesium. When using such ions with solid polymer electrolytes, which are advantageous due to their safety and robustness but have lower ion conductivities than liquid electrolytes, it is crucial to understand how to choose the polymer and anion type and ion concentration to optimize ion conductivity. Here, we apply a generic coarse-grained model that includes a potential of form Sr-4 between monomers and ions to capture ion solvation effects to show the impact of ion size and valency on ion dynamics in salt-doped polymer systems. We use molecular dynamics simulations with an applied electric field to calculate ion conductivity for a range of systems with mono- and di-valent cations at varied ion concentrations and anion sizes. We observe that increasing valency or lowering the anion size both tend to decrease the overall ion conductivity. The effect of solvation strength on these systems will also be discussed.