Interrogation of electrochemical properties of polymer electrolyte thin films with interdigitated electrodes

The ability to characterize bulk and interfacial transport properties of polymer electrolytes is critical to realizing their potential applications in electrochemical energy storage devices. In this study, we leverage custom microfabricated interdigitated electrode array (IDEs) as a platform to probe ion transport properties of polymer electrolytes films through electrochemical impedance spectroscopy (EIS) measurements. Using poly(ethylene oxide) (PEO) blended with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a model dry polymer electrolyte system, we investigate how geometric parameters of the IDEs influence the quality and analysis of EIS measurements. By focusing on films on the nanometer film thickness (ca. 50 nm), EIS measurements revealed diffusional processes near the electrode/polymer interface that may be difficult to observe with conventional thick films. Moreover, irreversible impedance spectra were observed at elevated temperatures when using IDEs with large electrode metal fractions. These irreversible processes were eliminated through passivation of the IDE with different oxides (SiO₂, Al₂O₃, or TiO₂). Ultimately, the ionic conductivity of PEO-LiTFSI electrolytes is confidently determined when appropriate IDE geometries and equivalent circuits are used. Our work demonstrates the use of IDEs and nanothin polymer electrolytes films as a versatile platform for rapid and efficient interrogation of both bulk and interfacial electrochemical properties.