Surface quality and I-V characteristics of laser Welded Thin foils of Copper/Stainless steel/Copper Stack for Lithium-Ion Battery Manufacturing

The production of lithium-ion batteries for electric vehicles relies heavily on the dissimilar welding of thin copper and stainless-steel foils using laser beams. Despite its technological advances, optimization strategies for stack welding of thin-foils still remains unexplored. This paper examines the feasibility of laser welding of copper/stainless steel/copper foil stacks using a 20 W nanosecond pulsed laser. The effect of scanning speed (250 to 300 mm/s) on the laser welding characteristics such as heat-affected zone (HAZ), surface roughness, microstructure and electrical resistance was systematically assessed. The results showed that enhancing the scanning speed reduced HAZ from 317.81 μm to 240.67 μm constituting a decrease of 24.27 % and surface finish got improved by 11.6 %. Microstructure of thin stacked foils revealed that the optimal metallurgical bonding and minimal porosity could be obtained at a lower scanning speed of 250 mm/s whereas higher scanning speeds can result in crack formation and incomplete fusion. Electrical resistance measurements using an Agilent B1500A semiconductor device analyzer demonstrated that impurities and interface defects significantly influence current-voltage (I-V) behavior, emphasizing the relationship between weld quality and electrical performance. Thus, a critical processing window for effective dissimilar welding of thin foils was established.