Effect of Thermal Aging on Nanoparticle Structure in Polymer Nanocomposite Electrolytes

Nanoparticles are commonly added to polymer electrolytes in order to concomitantly enhance their mechanical and ion transport properties. Previous work has shown significant increases in the ionic conductivity and Li-ion transference in nanocomposite electrolytes with inert, ceramic fillers. Mechanistic understanding of this property enhancement, however, assumes nanoparticle dispersion states--namely, well-dispersed or percolating aggregates--that are seldom quantified using small-angle scattering. In this report, we study the effect of thermal aging on the structure of a model nanocomposite electrolyte system--PEO:LiTFSI with 14 nm SiO₂ NPs--using small-angle x-ray scattering (SAXS). In agreement with similar studies on numerous polymer nanocomposite systems, we find a structure factor with a characteristic interparticle spacing that appears upon prolonged annealing. In parallel, we measure the ionic conductivity and dielectric relaxations of these materials. By combining these two techniques--SAXS and impedance spectroscopy--we hope to determine the effect of nanoparticle structure on the Li-ion conductivity of polymer electrolytes.