Role of chain architecture and composition on dynamics and ionic solvation in polyether-based electrolytes

Ion conducting polymers based on ethylene oxide (EO) repeat units are widely studied for use as electrolytes in lithium ion batteries. A molecular level understanding of the relationship between polymer chain architecture and ion conduction, however, remains unclear. We have compared the conductivity, ionic interactions, and polymer dynamics of a series of graft polyethers using a combination of impedance spectroscopy, vibrational spectroscopy, and atomistic scale molecular dynamics (MD). We find that side-chain length dictates large differences in the measured conductivity, despite modest differences in the calorimetric glass transition temperature (T_g) of the various materials. A temperature dependence in the conductivity of graft polyethers compared to linear PEO is explained by heterogeneous EO unit dynamics in the graft systems, arising from a comparatively immobile backbone. Importantly, these differences in polymer segmental mobility were not captured by experimentally observed T_g and were only apparent through the use of fine-grained MD simulations.