Enhanced Conductivity Pathways in Block Polymer Electrolytes with Homopolymer Additives

Block polymer (BP) electrolytes are an attractive alternative to current liquid electrolyte materials for lithium-ion batteries because of their ability to decouple ionic conductivity, modulus, and thermal properties, thereby enhancing performance and stability. To increase the ionic conductivity, A-b-B BPs were blended with A homopolymers, where A was the ion-solvating component, and doped with a series of lithium salts. The homopolymer distributions in the BP were determined via neutron reflectometry by leveraging the scattering length density contrast between deuterated homopolymer and non-deuterated BP. To access the wet and dry brush regimes, various homopolymer molecular weights were employed. The homopolymer distributions were correlated to the conductivity (via AC impedance spectroscopy) and glass transition temperature (via differential scanning calorimetry) to elucidate the effects of homopolymer blending on physical and transport properties. Finally, solid-state nuclear magnetic resonance spectroscopy was used to determine the effect of homopolymer blending on the relative populations of mobile and immobile lithium ions in the nanostructured polymer blend electrolytes.