Characterization of Ion Transport in Asymmetric Block Copolymer Electrolytes*

Polystyrene-b-polyethylene oxide (SEO) is an attractive material for enabling lithium metal anodes for secondary batteries. Microphase separation due to competing enthalpic and entropic interactions yield nanostructures which decouple the mechanical and ion conducting properties. SEO electrolytes are synthesized by adding a lithium salt, lithium bis(trifluoromethanesulfonyl)imide for this work. Ion transport has been studied in SEO electrolytes where the volume fraction of polyethylene oxide (PEO) is in the range of 0.4-0.6 and lamellar morphologies are observed via small angle X-ray scattering (SAXS). This work expands on the existing literature by examining SEO electrolytes with volume fractions of PEO in the range of 0.7-0.9 and 0.2-0.3 and which exhibit a variety of morphologies including body centered cubic spheres and hexagonally packed cylinders. Ionic conductivity, cation transference number, and salt diffusion coefficient are reported as functions of salt concentration and related to morphology.