Unveiling Chemomechanical Degradation in Aqueous Batteries with Online Acoustic Emission Sensing

Online acoustic emission (AE) sensing is a promising nondestructive technique for battery health monitoring. Herein, we report on the ability of AE sensing to differentiate among different chemomechanical degradation events in a TiS2-based model aqueous chemistry. Short and high-frequency AE signals primarily stem from fracture-related degradation of TiS2, such as layer delamination, exfoliation, and cracking. Longer and lower-frequency signals originate from gas bubbles bursting when the cell is cycled outside the water stability window. The two processes demonstrate distinct AE features, allowing them to be semi-quantitatively distinguished from both time and frequency domains. Complementary physicochemical characterizations have been conducted to correlate with the AE observation, including online electrochemical mass spectrometry, operando synchrotron X-ray diffraction, and ex situ scanning electron microscopy. Our work indicates that online AE sensing holds the promise to identify complex chemomechanical degradation processes in rechargeable batteries.