The effect of chemical structure on the morphology, ion transport, and modulus of hybrid inorganic-organic diblock copolymer electrolytes

Poly(ethylene oxide)-b-polyhedral oligomeric silsequioxane (PEO-POSS) mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is a nanostructured hybrid organic-inorganic diblock copolymer electrolyte that may enable lithium metal batteries. The organic poly(ethylene oxide) block solvates lithium ions and facilitates ion transport while the inorganic polyhedral oligomeric silsequioxane (POSS) block provides mechanical rigidity, decoupling typically antagonistic mechanical and ion conducting properties. PEO-POSS with different alkyl chain substituents on the POSS monomer’s silica cage were synthesized to study the effect of chemical structure on morphology, ion transport, and modulus. Ionic conductivity, salt diffusion coefficient, and steady-state cation transference number were measured for a range of salt concentrations. In general, increasing the alkyl chain length was found to promote ordering and increase mechanical stiffness, while decreasing ionic conductivity.