Characterization of Laser Welded Joints between Copper Tabs and Multi-layered Foils in Li-Ion Battery

The rapid expansion of electric vehicles and energy storage systems requires lithium-ion batteries with simultaneously high energy density and reliability. In this regard, the joint between the copper (Cu) current collector and the Cu tab becomes a critical determinant to represent cell performance and safety. However, Cu exhibits low absorptivity under infrared ray lasers and high thermal conductivity. These material characteristics disturb stable keyhole formation and molten pool flow, which result in weld defects. Relevant studies proposed high-power green and blue lasers, beam shaping, and spatial beam oscillation; however, they remain limited to provide the fundamental process knowledge enabling stable and persistent use of infrared ray lasers, which have been widely installed in production lines. This study presents the empirical analysis to characterize laser welded joints between Cu tabs and multi-layered foils in the infrared ray laser. In this study, welding tests are conducted on a joint of a Cu tab and multi-layered foil using a TruDisk 8000 infrared disk laser. Design factors are tab thickness (0.4, 0.5, 0.6 mm), foil thickness (5, 6, 8 ㎛), and the number of foil layers (5, 10, 20). Weld performance is evaluated through bead appearance inspections and tensile shear strength (TSS) tests. The maximum TSS for 5 layer stacks is measured, wherein a peak strength of 10.79 kgf is achieved with a combination of a 0.5 mm tab and 6 ㎛ foil on a 20-layer stack. The experimental results provide fundamental knowledge to correlate design factors with the joint strength in Cu foil-tab welding assembly.