The growing prominence of the electric vehicle industry, fueled by environmental concerns, has demanded innovation in various aspects of battery technologies with special emphasis on increasing the efficiency of both electric storage and its retrieval. An unexplored area of this is to identify the possibilities and limits of laser soldering. Here, we reveal the effects of surface pretreatment conditions and the amount of filler, along with the laser power and irradiation time on the characteristics of laser-soldered joints, by simultaneously evaluating the electrical and mechanical behavior of laser-soldered nickel-plated steel sheets (Hilumin®). By describing the morphological characteristics of the resolidified solder and the electrical and mechanical properties of the joints, we identify three, characteristically different morphological appearances and highlight the optimal one, where uniform and mostly void-free solder can be produced. Furthermore, we report a correlation between the threshold of upper sheet melting (either expressed as laser power or irradiation time) and joint deterioration in terms of the electrical and mechanical properties of the joint. We conclude that laser soldering can create joints with outstanding electrical conductance and adequate mechanical stability that meets the critical specifications of battery joining technologies when the surface pretreatment condition and processing parameters are properly optimized.

Nowadays, lasers are routine tools in the widest range of materials processing, including welding of battery packs. The properties of the laser generated weld bead are crucial in determining the electrical and mechanical behavior of the joint. Here, we report on the identification of five morphological bead types, namely, Rosenthal, single wave, elongated, pre-humping, and humping morphologies and their systematic appearance over the laser power versus scanning speed plane. We prove that each type exhibits characteristic electrical and mechanical behavior that differ not only in the magnitude of relevant materials’ properties, but also in their variability. We show for nickel-coated steel and uncoated DC01 cold rolled steel that the so-called single wave morphology is best suited for battery welding applications, since this morphology class concomitantly exhibits the lowest electrical resistance and the highest mechanical strength, both with a relatively small margin of error. The results suggest that the bead morphology could be exploited as a simple indicator of joint properties.

With the proliferation of electric drivetrains, the development and optimization of joining techniques for the fabrication of battery packs became a prime manufacturing topic. Decreasing the electrical resistance and increasing the mechanical strength of the welds at the individual cell level are of great importance not only for productivity and efficiency but also for safety and sustainability purposes. Lasers offer an advanced, highly automatable solution for battery cell joining. Usually, the optimization focuses on the laser parameters or the scanning speed. However, the most widespread battery welding geometry, the so-called lap geometry, allows alternative possibilities for joint property optimization. The novelty of our approach is that we focus on systematic experimental investigation of the effects of dimensional parameters and the layout of the weld pattern. Systematic experiments reveal that the shape and size of the weld area have substantial effect on the properties of the laser welded joint. Our results prove that a rather substantial gain can be achieved in both the electrical and mechanical properties when the weld consists of at least two parallel bead segments. We also show that it is beneficial by both means if the segments have the greatest individual length and placed apart at the maximum feasible distance. The orientation of the straight segments affects the mechanical and electrical behavior differently: strongest welds consist of weld segments oriented in parallel, while the smallest resistance can be achieved using segments oriented perpendicular to the direction of current flow, respectively.

Following an overview of conventional bonding techniques used for the assembly of battery packs of modern hybrid vehicles special attention will be paid to laser keyhole welding. The unique challenges of aviatic applications, especially joining large number of batteries in a highly reproducible manner are pinpointed. The effect of contact area on the electrical and mechanical properties of laser welded joints is investigated on a DC01 steel model structure. The results are also discussed in terms of laser scanning speed. In the optimal process parameter range joints exhibiting electrical and mechanical properties appealing for assembling hybrid aircraft battery packs can be produced with high reproducibility.