Ultrasonic phased array imaging of gas evolution in a lithium-ion battery

Non-invasive characterization and monitoring of gas evolution during the operation of commercial Li-ion batteries (LIBs) has been a long-term challenge. This paper presents an in situ subsurface ultrasonic array imaging method to detect, locate, and characterize gases generated inside a LIB. Ultrasonic signals scattered from internal gases are collected by a full matrix capture method. A cross-section image showing gases is produced using the velocity-modified total focusing method. The locations and distribution of the gases in both the lateral and thickness directions can be clearly revealed. The finite element simulations and a controlled experiment are performed to validate the feasibility of the proposed array imaging method. Finally, a realistic long-term cycling experiment is performed on a commercial pouch cell. The appearance, evolution, and accumulation of gases are visualized and characterized by analyzing the images produced at different cycles. The experiment findings are validated against the X-ray CT results.