Phase behavior and Li+ Ion conductivity of styrene-ethylene oxide multiblock copolymer electrolytes

Solid polymer electrolytes are attractive materials for use as battery separators. Here, a molecular weight series of polystyrene-polyethylene oxide (PEO) multiblock copolymers was synthesized by the thiol-norbornene click reaction. The subsequent materials were characterized both neat and with a lithium bis-(trifluoromethane)sulfonimide salt loading [(Li)/(EO)] of 0.1. In general, neat samples demonstrated crystallinity scaling with PEO content. Lithium ion-containing samples had broad scattering peaks, half of which displayed disordered scattering, even at the lowest block molecular weights (polystyrene=1kg/mol, PEO=1kg/mol). Fitting of disordered scattering data, using the random phase approximation, yielded (RPA) and R-g values that were compared with recent predictive work by Balsara and coworkers. The predictions were accurate near the volume fraction f(PEO)=0.5 but deviated symmetrically with volume fraction asymmetry. Samples were also analyzed by electrochemical impedance spectroscopy for their potential to conduct lithium ions. Samples with f(PEO)0.5 demonstrated robust conductivity, whereas samples below this volume fraction conducted very poorly, with one exception (f(PEO)=0.24). This work expanded upon our recently reported approach to multiblock copolymer synthesis, demonstrating the improved access of materials to further our fundamental understanding of multiblock copolymers. Copyright (c) 2016 John Wiley & Sons, Ltd.