For the safety of the lithium-ion batteries widely used for electrical cars and Energy Storage Systems (ESS), maintaining a solid welding connection between a battery cell and a busbar is critical. For example, dozens of battery cells are wire-connected to the busbars of the ESS, and any single failure of the wire welding will result in shutdown of the entire ESS and pose a significant safety risk. Currently, destructive shear force tests are conducted only for a few selected samples, but not for exhaustive real-time inspection. In this study, a laser ultrasonic system is developed for noncontact, nondestructive and real-time inspection of wire welding of lithium-ion batteries. Ultrasonic waves are generated using a pulse laser at a wire, and the corresponding responses are measured before and after the welding point. A weld defect is detected, when the ultrasonic energy substantially attenuates after passing through the welding point. The performance of the proposed inspection technique is examined by inspection over 300 wire welding points of the ESS.
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