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

• Published in: Polymers for advanced technologies 2016-07, Vol.27 (7), p.946-954
• Main Authors: Sarapas, Joel M, Saijo, Kenji, Zhao, Yue, Takenaka, Mikihito, Tew, Gregory N
• Format: Article
• Language: English
• Subjects: Copolymers; Electrochemical impedance spectroscopy; Electrolytes; Lithium; Molecular weight; Oxides; Scattering; Volume fraction
• ISSN: 1042-7147; 1099-1581
• DOI: 10.1002/pat.3753

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 chi sub(R)PAand R sub(g)values that were compared with recent predictive work by Balsara and coworkers. The predictions were accurate near the volume fraction f sub(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 sub(PEO) greater than or equal to 0.5 demonstrated robust conductivity, whereas samples below this volume fraction conducted very poorly, with one exception (f sub(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.