<p>Metal-thermoplastic composite foil is an ideal candidate for next-generation positive current collectors in lithium-ion batteries, as it significantly enhances battery safety and energy density. However, the bonding mechanism between the multi-layer metal-thermoplastic current collectors and the tabs remains unclear, and the welding process is cumbersome. This study focuses on investigating the bonding mechanism of multi-layer metal-plastic current collectors with tabs. To ensure current conduction and weld formation, 20-μm-thick 1060 Al foils (serving as compensation metals) and Al-PET foils were alternately stacked into a 10-layer assembly, which was then ultrasonically welded to a 0.3-mm-thick 1060 Al sheet. Results indicate that the PET layer is not displaced first to enable metal-metal contact for metallurgical bonding. Instead, adhesive bonding first occurs between the Al foil and the Al coating. Following the gradual collapse of the laminated structure, the compensation metal—accompanied by the Al coating—undergoes material mixing with PET. These mixed materials come into contact with the Al tab. The bonding process transitions from mechanical interlocking to atomic diffusion, ultimately achieving metallurgical bonding. This behavior differs distinctly from that of traditional metal foils, where inter-layer bonding occurs while the multi-layer structure is preserved. Importantly, for battery operation, current transmission between the current collector and tab relies on the metallurgical bonding regions at the welding teeth; nonetheless, material filling between the welding teeth also provides additional current paths. Although the collapse of the laminated structure at the welding teeth introduces more compensation metal (thus reducing resistance), such structural damage concurrently decreases tensile strength. Notably, fragmentation of the plated metal within the bonding area is inevitable but exerts negligible influence on resistance.</p>