Does Ion Aggregation Impact Polymer Dynamics and Conductivity in PEO-Based Single Ion Conductors?

Abstract

We describe quasi-elastic neutron scattering measurements of polymer backbone dynamics in PEO-based single ion conductors with varying morphologies. These morphologies include aggregates, multiplets and ion pairs, where the dominant ion state varies with cation identity: Li+ samples are mostly aggregates, Cs+ samples are mostly ion pairs, and Na+ samples contain a range of ion states. The conductivities of these samples are roughly equivalent, suggesting that ion state does not have a large impact on conductivity. Because conductivity is connected to polymer dynamics, we use quasi-elastic neutron scattering to assess polymer dynamics in all three samples. In all three ionomers, the motion of the PEO spacer is slower near the ionic comonomer [anchor atoms] than it is in the spacer midpoint [bridge atoms], leading to two fractions in the measured dynamics. Anchor atom dynamics depend on cation content but not on the different morphologies associated with cation identity. We thus conclude that for this syste...