The role of polymer melt viscoelastic network behavior in lithium ion transport for PEO melt/LiClO4 SPEs: the “wet gel” model

Earlier light scattering studies revealed that melts of the electrolyte polymer poly(ethylene oxide) (PEO) were not homogeneous but were instead structured and behaved as elastic PEO networks. We report the results of subsequent viscometry measurements that provide a more complete picture of PEO melt structure and dynamic behavior. We find that PEO melts behave as “wet gels,” i.e., they behave as elastic PEO networks immersed in a PEO fluid that retards network motions. In addition, a preliminary light scattering examination of the role that PEO melt network dynamic behavior might play in lithium ion transport found that although the light scattering relaxation function mode structure of PEO melt/LiClO4 solutions changed significantly when the salt concentration was increased from 0 to 20 wt.% — the latter concentration being that for which maximum conductivity in the PEO/LiClO4 system has been reported — the network structure and behavior of the melt was retained. Finally, we report the results of exploratory investigations of several aspects of PEO melt behavior that provide promising directions for future studies of this interesting and important system.