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 TiS 2 -based model aqueous chemistry. Short and high-frequency AE signals primarily stem from fracture-related degradation of TiS 2 , such as layer delamination, exfoliation, and cracking. Long and low-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 batteries with liquid and potentially solid electrolytes. • Online acoustic emission sensing identifies battery chemomechanical degradations. • Bursting of gas bubbles shows a long rise time and low frequency. • Particle delamination and cracking show a short rise time and high frequency. • Concentrated aqueous electrolytes mitigate hydrogen evolution in aqueous batteries.