Ion-Transport Properties of Nanothin Film Dry Polymer Electrolytes

Polymer electrolytes have demonstrated promise as dry electrolyte materials to enable lithium-metal batteries. However, majority of studies have focused only on thick samples (100’s of microns). However, interfaces play a critical role on the performance of batteries, thus investigating polymer electrolyte in the context of nanothin films (5-100 nm) will lead to better understanding of the role of interfaces on charge transport properties. Here, we report on ion transport characteristics of nanothin films of PEO and LiTFSI blends as a function of salt concentration, temperature and film thickness. Ion transport measurements were successfully performed using impedance spectroscopy on films fabricated on custom-designed nanofabricated interdigitated electrode (IDE) devices. Importantly, thickness dependence study of ion transport shows a monotonic decrease in ionic conductivity upon decreasing film thickness from 250 nm to ca. 10 nm, and the effect is stronger at low salt concentrations. The decrease of ionic conductivity at thinner films originate from the increasing fraction of the immobilized layer near the polymer/substrate interface. Our results suggest that using nanothin film configuration is a promising strategy to probe interfacial effects on ion conducting properties.