Nanofabrication for Probing Ionic Conductivity Mechanisms in Thin-Film Polymer Electrolytes

Ion conducting polymers as solid electrolytes enable the use of high energy density batteries and offer a safe, lightweight, and flexible alternative to traditional liquid electrolytes. However, they suffer from lower room temperature conductivities and Li ion transference numbers than their liquid counterparts as well as poor electrochemical stability. Therefore, it is important to study the ion transport mechanisms within these materials in order to maximize conductivity while retaining these advantageous properties. In this study, we fabricate interdigitated electrode devices with trenches of insulating dielectric SiO₂ on the length scale of an insulating block in a block copolymer such as PS-b-PEO. These devices are fabricated so that a percentage of the trenches, which model the conducting pathway of a BCP, are blocked by additional SiO₂. A PEO/LiTFSI solution is spincoated and reflowed onto the devices then measured using AC impedance spectroscopy to calculate the conductivity. We report a decrease in conductivity with increasing percent hindered pathways. By eliminating the effects of grain boundaries and interfacial blurring between blocks of a block copolymer, this study elicits a direct relationship between structure and conductivity.