The Effect of Composition on the Morphology of Hybrid Inorganic-Organic Diblock Copolymer Electrolytes

Block copolymer electrolytes are advantageous for applications in lithium batteries due to chemical stability and tunable nanostructures. Inorganic-organic diblock copolymer electrolytes couple the ionic conductivity and mechanical strength desired in polymer electrolytes and exhibit microphase separation due to internal repulsive interactions, leading to unique phase transitions. The phase behavior of poly(ethylene oxide) (PEO)-block-polyhedral oligomeric silsesquioxane (POSS) acrylate, synthesized using nitroxide-mediated radical polymerization (NMP), with lithium bis(trifluoromethane)sulfonimide (LiTFSI) salt is systematically studied by varying the diblock composition and salt concentration. Using small angle X-ray scattering (SAXS) at different temperatures the morphology and the Flory-Huggins interaction parameter is obtained to quantify the thermodynamic interactions within the system. Due to the high degree of conformational asymmetry and strong repulsive interactions between the two polymer blocks, the morphological study reveals phase transitions that are not traditionally observed in diblock copolymers.