Evaluating Interfacial Stability in Solid-State Pouch Cells via Ultrasonic Imaging

Chemical/electrochemical stability at the interfaces greatly affects the performance of solid-state batteries (SSBs). However, the interfacial behavior in SSBs remains elusive due to the subsurface nature of interfaces and the lack of proper characterization methods. Herein, ultrasonic imaging is employed to nondestructively investigate the interfacial stability in solid-state pouch cells. Benefiting from the high sensitivity of ultrasound to the gas/vacuum, operando ultrasonic imaging can effectively probe the inner gas release and interfacial degradation in pouch cells during long-term cycling. The gradual oxidation at the cathode interface is tracked, while the increased interfacial resistance from either contact loss or passivation layer growth is well distinguished. Moreover, the safety issue of SSBs is highlighted by the flammable gas release detected in ultrasonic images. Ultrasonic imaging is demonstrated to be a powerful tool to evaluate the interfacial stability in SSBs, which can guide the rational design of interfaces and enhance the performance of SSBs.