Ultrasonically assisted resistance welding of multilayer thin films-to-tab for battery cell manufacturing

For vehicle electrification, battery manufacturing and assembly is of high importance. At the basic cell level, the pouch cell is commonly used and contains multilayer of thin films as electrodes, which need to be welded to lead tabs for the module level assembly. As the most elementary unit, the integrity and robustness of these electrode-to-tab welds are critical for the safety and efficiency of the whole battery pack. Ultrasonic metal welding is predominantly employed for this multilayer stack welds, however, the inherent shear motion brings concerns on the severe deformation of top films and potential damage on the existing welds. Laser welding is an alternative promising approach, however, the porosities issues in Al joints are the main challenges. In this study, a recently developed hybrid process, ultrasonic-assisted resistance spot welding (URW) shows the effectiveness in achieving successful multilayer Al and Cu films-to-tab welds with minimal weld discontinuities of either porosities or cracks. In this URW process, the ultrasonic vibration is applied perpendicular to the weld interface during the passage of electrical current in resistance spot welding (RSW). The weld microstructure and mechanical properties are comprehensively evaluated under different electrical current and ultrasonic parameters. The mechanisms of ultrasonic enhancement of the weld performance are explained, presenting URW as a new promising process in multilayer thin films joining.