Prognosticating nonlinear degradation in lithium-ion batteries: operando pressure as an early indicator preceding other signals of capacity fade and safety risks

Lithium-ion batteries occasionally experience sudden drops in capacity, and nonlinear degradation significantly curtails battery lifespan and poses risks to battery safety. However, methods for pinpointing and forecasting the knee-point of nonlinear degradation based solely on electrical signals are not yet timely. In this research, we monitored stress development during extended cycling by conducting precise operando pressure measurements on confined pouch cells. We observed that irreversible cumulative mechanical pressure signals precede the onset of nonlinear battery degradation as indicated by electrical signals. Furthermore, we delved into the mechanism behind pressure signals' ability to foretell the knee-point earlier than electrical signals, which was further substantiated through in-situ and post-mortem analyses. Moreover, we carried out a theoretical dissection to separate the pressure contributions from the anode and cathode, aiming to correlate the pressure profile evolution at the electrode and cell levels with various degradation modes. This proof-of-concept study, spanning the entire battery lifecycle, has shown that pressure signal monitoring can swiftly differentiate between distinct degradation modes. Consequently, this work clears the path for the deployment of simple pressure sensors mounted on the battery surface to diagnose battery degradation pathways.