Enhanced ion transport in block polymer electrolytes through the manipulation of salt and monomer segment distributions

Solid block polymer (BP) electrolytes for lithium-ion batteries can address safety and performance concerns present in conventional liquid-state electrolytes, but the ion transport in BPs requires significant improvement to meet the demands of current and future battery applications. Transport properties in nanostructured BP electrolytes can be enhanced through the modification of salt and monomer segment distributions within the ion-conducting domain. We explored two methods to tune these distributions: the synthesis of polystyrene-block-poly(oligo-oxyethylene methacrylate) (PS-b-POEM) BPs with gradient or random copolymer regions at the chemical junction between the PS and POEM blocks (i.e., tapered block polymers) and the blending of POEM homopolymers of different molecular weights into PS-b-POEM BPs. For both methods, we connected the structural characteristics, such as the salt and monomer segment distributions, determined by X-ray and neutron reflectivity, to the segmental and ion dynamics measured through differential scanning calorimetry, ⁷Li solid-state NMR, and AC impedance spectroscopy. These results elucidated design parameters in the synthesis and fabrication of BP electrolytes that can increase ionic conductivity.