Improving Lithium Conductivity in Surfactant-Like Multiblock Copolymers through Selective Solvent Swelling

In previous work, we identified a variety of period morphologies in multiblock copolymers comprised of alkyl blocks of a fixed length strictly alternating with polar blocks having one lithium sulfonate group. As a function of alkyl block length and temperature we observed layered, double gyroid, and hexagonally-packed cylindrical morphologies. The addition of DMSO selectively swelled the polar blocks and increased ionic conductivity by 10^4. This work explores the effect of a wide variety of selective solvents on lithium conductivity as measured by electrochemical impedance spectroscopy. X-ray scattering detects morphological changes and IR spectroscopy elucidates the local lithium environment. The experiments are complemented by all atom molecular dynamics simulations. Swelling with propylene carbonate proves to be more effective at increasing lithium conductivity than swelling with ethylene carbonate or diglyme. Insights from these techniques will guide rational solvent selection for enhanced conductivity in polymer electrolytes.