In-depth evaluation of laser welding of thick busbar to 21700 Li-ion cell terminal for electric supercar vehicle battery pack

High-performance supercars using Li-ion batteries necessitate thicker aluminium busbars with thin steel joints. However, joining these materials often leads to overheating resulting in brittle intermetallic compounds (IMCs), reduced weld quality, and higher electrical resistance. This study evaluated, laser wobble welding of a nickel-plated Al busbar of 0.9 mm thickness with a 0.3 mm thin 21700 cell nickel-plated steel terminal. An optimised joint using the wobbling method is implemented for the direct application to battery packs, satisfying the current carrying capacity with minimal electrical resistance and enhanced weld quality was generated. Elemental and microhardness analysis revealed the mechanism of IMC formation and observed that the brittle and therefore detrimental Fe2Al5 IMC predominantly forms near the protruding interface between Al-Fe solid solutions.