Characterization of morphology in ring-opening metathesis polymerized novel solid block copolymer electrolytes by atomic force microscopy and X-ray scattering

Block copolymers present the ability to design solid polymer electrolytes to include both ion conductivity and structural features which may lead to improved safety in lithium ion batteries. We report a morphology study of novel block copolymer electrolytes that were synthesized using ring opening metathesis polymerization. The monomers have an oxanorbornene dicarboximide backbone where the first block has oligomeric (n = 12) ethylene oxide (OEO) side chains and the second block has phenyl side groups. The former block achieves high salt solubility, while the latter block is a structural component with a high glass transition temperature. Block copolymers have been synthesized covering a range of compositions from 38 to 70 wt % of the phenyl containing block, and have been studied neat and with bis(trifluoromethane)sulfonimide lithium salt. The resulting morphologies were investigated using atomic force microscopy and small angle X-ray scattering (SAXS). Solvent vapor annealing was found to enhance ordering in the neat copolymer thin films and the addition of salt with solvent vapor annealing further increased long range order. Cylinder and lamellar structures dominate the observed morphologies and the addition of salt increases ordering and the range block copolymer compositions with lamellar structure. SAXS results demonstrate modest ordering, reinforce the observations from AFM, and show an increase in domain size with an increase in salt concentration.