Multi-frequency eddy current non-destructive evaluation of battery tab welding quality

The battery tabs are critical components connecting the battery to the circuit, and their welding quality directly influences the safety of electrical usage in batteries. Ultrasonic welding often induces thermoplastic deformation in the multilayer copper foil structure of the battery tabs, resulting in varying effective solid-phase bonding depths at the welding interface. However, conventional single-frequency eddy current testing (ECT) technique faces significant challenges in effectively characterising variations in welding quality. To address this issue, a Multi-Frequency Eddy Current ResNet (MFEC-ResNet) model is proposed. Firstly, the equivalent impedance variations at multiple frequencies are used as inputs to capture the complex relationships between multi-frequency features and welding quality. Secondly, multi-class focal loss is employed to tackle the class imbalance issue, enhancing the model’s ability to detect minority classes. Thirdly, Shapley Additive Explanations (SHAP) are used to interpret the contributions of individual features in the black-box model, providing insights into the model’s decision-making process. Experimental results show that the proposed multi-frequency ECT method achieves an accuracy of 95%, outperforming single-frequency ECT by nearly 10%.