In-situ measurement of drying and electrochemical-cycling-induced mechanical behavior and delamination of polypyrrole electrodes for energy storage applications

Abstract

Delamination during the fabrication and operation of thick electrodes is one of the major instabilities that prevent their utility for high energy density electrochemical devices. In this study, we investigate the deformation and delamination of polypyrrole (pPy) film electrodes using in-situ measurements of curvature/stress. At the beginning of drying process, the water in the film exited continuously, while the film did not deform accordingly. Then, the film rapidly contracted near the end of the evaporation process and remained in its equilibrium contracted state. The film deformation was found to be caused by the evaporation of moisture near the polymer chain, whereas it was not affected by the evaporation of free water in the pores, causing the mismatch between the deformation and evaporation. Importantly, film delamination was identified in real time as the rapid stress drop corresponded to the peeling of the film from the substrate. The interfacial fracture energy was quantified to estimate the adhesion strength of the interface with various treatments. Moreover, electrochemical-cycling-induced delamination was successfully identified based on the type of delamination. We believe this study would be beneficial for both the development and operation of thick electrodes with high energy density and stability.