Dynamic Patterning in PEO-Based Single Ion Conductors for Li Ion Batteries

We use quasi-elastic neutron scattering (QENS) to study polymer dynamics in PEO-based single ion conductors (ionomers) where the anion is covalently bonded to a PEO spacer through a comonomer unit, so that only the cation contributes to conductivity. We compare the effects of changing ion content on the dynamics of the polymer spacer in two ways by varying the ratio of ionized to nonionized monomer units and by changing the spacer length. In both cases, two dynamic classes of spacer atoms are observed: we associate these classes with bridge atoms located in the midspacer region and anchor atoms located near the ionized comonomer. Because these dynamic classes are associated with different spatial regions on the PEO spacer, we propose that fast [bridge] and slow [anchor] regions are spatially segregated. We use QENS to determine the fraction of bridge and anchor atoms and estimate their ionic compositions. We further combine this with X-ray scattering to assess the degree of ionic phase separation and propose schematics of dynamic patterning in single ion conductors.