Effect of Confinement on Ion Transport in Polymer Electrolytes

Understanding ion transport in polymer electrolytes is important for elucidating the molecular origins of transport limitations and opportunities in nanostructured solid polymer electrolytes for lithium batteries. Here, we use all-atom molecular dynamics simulations to elucidate how cylindrical confinement regulates the structure and dynamics of poly(ethylene oxide) (PEO)-based electrolytes. Decreasing the nanotube diameter drives pronounced polymer chain segregation and reorganizes the spatial distribution of coordinating oxygen sites. This confinement-induced structural rearrangement markedly suppresses ion-segment codiffusion along short chain segments and inhibits interchain hopping, leading to a substantial decrease in Li+ mobility. However, upon decreasing nanotube diameter, Li+-EO coordination becomes stronger, which amplifies distinct cation-cation correlations; this competition between slowed ion mobility and strengthened ion-ion correlations gives rise to a nonmonotonic dependence of ionic conductivity on nanotube diameter. To disentangle geometric confinement from specific polymer electrolyte-wall interactions, we perform control simulations with hard walls, where the hard wall provides only steric exclusion; these results confirm that the nonmonotonic trend cannot be explained by geometric confinement alone and instead requires the inclusion of specific polymer electrolyte-wall interactions. Together, our results reveal the intricate coupling among confinement geometry, interfacial interactions, polymer organization, and ion transport, providing an atomistic basis for understanding ion transport in nanochannel-confined polymer electrolytes.