Quasi-Continuous Wave Fiber Laser Welding of Steel–Copper–Steel Sandwich Tab to Nickel-Plated Copper Busbar for Li-Ion Battery Packs

Abstract The growing demand for electric vehicles (EVs) has driven significant advancements in battery technology, particularly in battery packaging systems. A critical safety and performance aspect of these systems is the reliable and efficient joining of battery components, such as the busbar to tab interconnectors. Traditional joining techniques, such as ultrasonic welding, resistance spot welding, and soldering, are widely used in battery manufacturing, which have certain inherent limitations in terms of materials and productivity. Laser welding is capable of joining a wide range of materials, including dissimilar metals, with reasonable speed and accuracy. The quasi-continuous wave (QCW) fiber laser is particularly well-suited for the precision demands of battery manufacturing. Its ability to finely adjust energy output and pulse duration ensures high-quality welds. This paper investigates laser overlap welding using a QCW laser for producing tab-to-busbar interconnectors for Li-ion battery assembly. In this research, a 1.5 mm thick electro-nickel-plated copper (Cu [Ni-plated]) busbar and a 0.2 mm thick steel–copper–steel (SS–Cu–SS) sandwich tab were welded using QCW 6 kW pulsed laser. The effects of key process parameters, laser power, laser frequency, pulse duration, and scan speed on mechanical bond failure load, electrical contact resistance, weld morphology, bead width, and microhardness distribution have been studied. The maximum failure load was found to be 610 N, with the lowest contact resistance, 150 μΩ, achieved under closely spaced pulses.