Micro Friction Stir Spot Welding for Copper Current Collector Applications - An Experimental Study

The growing demand for advanced energy storage systems, power electronics, and electrical interconnections requires joining processes that ensure both electrical conductivity and mechanical stability. Applications such as battery cell-internal contacts, flexible busbar connections, and printed circuit board (PCB) conductor interfaces impose strict requirements on material combinations, layer thicknesses, and thermal management, which influence the suitability of the joining processes. Micro friction stir spot welding (µFSSW) offers advantages through its low thermal impact as well as its high process robustness and through the bonding of the joining partners in solid state. In the studies presented in this article, transferable simplified specimens were designed to systematically evaluate process parameters for different applications of µFSSW. The feasibility of a full contact using µFSSW was assessed through electrical resistance measurements, mechanical shear testing, and morphological examinations of the weld zone, as well as axial force measurements during the welding process. The results demonstrate the suitability of µFSSW for copper-based current collector foils in cell-internal contacts, busbar interconnections, and PCB junctions, and they highlight key relationships between the process conditions and the electrical, mechanical, and structural performance. The study also highlights challenges and opportunities for a future industrial implementation.