Leveraging conductivity-enhancing pathways in homopolymer-blended block polymer electrolytes*

Block polymer (BP) electrolytes are appealing alternatives to liquid, gel, or homopolymer systems because the mechanical, thermal, and conductive properties are decoupled such that enhanced stability and performance are achievable. As a method to increase conductivity, polystyrene-b-poly(oligo-oxyethylene methacrylate) [PS-b-POEM] BPs were blended with a more mobile, ion-conducting POEM homopolymer; the blends then were doped with lithium salts. By adding homopolymers of different molecular weights, wet brush or dry brush regimes were achieved, as confirmed via neutron reflectometry. The wet brush polymer blends increased the mobility of both the polymer and lithium as suggested by the reduction of T_g,POEM and via line narrowing in variable temperature Li-7 solid-state nuclear magnetic resonance measurements, respectively. However, the dry brush blend demonstrated an overall higher ionic conductivity, likely due to the presence of homopolymer-rich ion channels. The results of this study provide key design parameters to promote enhanced conductivity via homopolymer-rich pathways in BP-based electrolytes.