Ion Transport in Free-standing Mixed Ionic-electronic Conducting Liquid Crystal Thin Films

In this work, we designed mono and di-functionalized mixed conducting liquid crystals that are able to be crosslinked for making free-standing liquid crystal thin films. We found that the liquid crystal microstructure can still be well retained after UV crosslinking reaction evidenced by grazing incidence wide-angle X-ray scattering (GIWAXS) and providing promising thin film mechanical properties. The ion transport in the liquid crystals is realized by loading with lithium salt, lithium bis(ttrifluoromethanesulfonyl) imide (LiTFSI) with the material able to maintain LC packing up to r = [Li⁺]/[EO] = 0.05. We adopted a combination of experimental and molecular dynamics simulations to understand the complex interplay between self-assembly behavior, solvation structure, crosslinking extent, and ion diffusion. The highest ion transport is achieved by tuning the ratio between mono and di-functionalized liquid crystals to be 10:1 at a salt concentration of r = 0.01 with conductivity of 8×10^-5 S/cm with tensile modulus higher than 50 MPa showing such material’s potential serving as patternable solid-state polymer electrolytes. Further, we demonstrated a general trade-off between mechanical properties and ion transport as a result of limited solvation capability.