Noncontact laser ultrasonic inspection of weld defect in lithium-ion battery cap

Abstract

The continuous development of electric vehicles and electronic devices has increased the demand for lithium-ion batteries. In this study, a laser ultrasonic inspection system was developed for the noncontact and nondestructive inspection of the laser welding conditions of a cylindrical lithium-ion battery cap. An Nd: YAG pulse laser was used for Lamb wave generation on the battery cap. Lamb waves were measured from the front surface of the battery cap using a laser Doppler vibrometer. The bending stiffness of the battery cap decreased as the welding condition deteriorated, and the Lamb wave amplitude was amplified. Accordingly, an automated defect detection algorithm for inspecting welding conditions was developed. The effectiveness of the proposed inspection system was theoretically and experimentally evaluated using actual cylindrical battery caps. The battery cap weld inspection accuracy exceeded 89 %, correctly identifying seven defective and ten intact battery caps out of eight defective and 11 intact battery caps, respectively. The numerical simulation indicated that the Lamb wave amplitude increased at the weld joint, demonstrating consistency with the experiment results. The proposed system is promising for the in-line inspection of battery caps because it facilitates high-speed, noncontact, and nondestructive inspection. Furthermore, the proposed inspection system can detect invisible weld defects on the back surface of a battery cap by inspecting its front surface.