Ion Coordination and Clustering-Assisted Lithium Transport in Polymeric Ionic Liquids: A Molecular Dynamics Study

Abstract

Polymerized ionic liquids (PILs) are promising solid-state electrolytes for lithium batteries, but the molecular mechanisms governing lithium-ion transport remain poorly understood. Here, atomistic molecular dynamics simulations were employed to investigate ion transport, polymer dynamics, and microstructural evolution in poly(1-ethyl-3-vinylimidazolium) bis(trifluoromethanesulfonyl)imide (PEVIM+–TFSI–) doped with LiTFSI over a lithium concentration (χLi) of 0.0–0.4. Li+ preferentially coordinates with TFSI– sulfonyl oxygen atoms, with an average Li+–O(TFSI) coordination number of approximately 4–5, inducing partial reorganization of the polymer–anion network. The Li+ diffusivity and ionic conductivity exhibit non-monotonic concentration dependence, with maximum transport at χLi = 0.2. Coordination-state analysis indicates that lithium transport predominantly occurs through cluster-assisted exchange involving Li+–TFSI– aggregates. At higher χLi, these aggregates become more dynamic, establishing a structure–dynamics–transport relationship governing lithium-ion conduction in PIL-based electrolytes.