Influence of Polymer Architecture on Phase Diagram, Ionic Conductivity, Free Volume, and Rheology in Poly (ethylene oxide) (PEO) Based Liquid Polymer Electrolytes

This study deals with the application of various architectures (linear, stars, and hyper-branched) of PEO and lithium contents to explore the effects of polymer architecture and salt content on the glass transition (T_g), crystallization, mechanical properties, and ionic conductivity of PEO based electrolytes. The phase diagrams showed strong dependence on the PEO topology such that PEOs with higher branching and salt ratios show lower crystallinity and melting temperature (T_m) in both their neat form and its electrolytes. Moreover, the addition of salt increasingly resulted in higher T_g values with decreasing T_m in all electrolytes. Additionally, the salt concentration-dependent Li-ion conductivities, which maximized at the molar ratio of [Li/EO = 0.085] for all architectures, showed that non-linear architectures with higher functionality had as much as 3x higher ionic conductivity than the linear analogue, which could be attributed to higher free volume probed by Positron Annihilation Spectroscopy and lower bulk viscosity in branched architectures with increasing functionality. Eventually, increasing the salt concentration further than [Li/EO = 0.085] always led a decrease in ion transportation due to formation of ion accumulation and clusters.