Influence of the surface properties of the connector material on the reliable and reproducible contacting of battery cells with a laser beam welding process

The increasing electrification of the automotive industry leads to a growing demand for high-performance energy storage systems. Three different cell types are used for the construction and production of battery modules or packs. These include, for example 18650 round cells, prismatic cells or pouch cells. For the electrical interconnection of prismatic energy storage devices or round cells, the laser bonding method can be used as a particularly flexible connection technology. This method combines the technique of a conventional wire bonder with laser beam welding. Compared to wire bonding, wider and thicker connectors can be contacted, and thus higher currents can be transmitted. During the production of wires/ribbons for wire bonding, sometimes complicated and costly process steps are necessary in order to ensure a consistently high quality of the produced material and consequently obtain a reproducible wire bonding process. Unfortunately, a polished and hence highly reflective surface of an aluminium or copper ribbon adversely affects the reliability of the laser beam welding process. A rough or oxidised ribbon surface however can favour the coupling of the laser radiation into the copper material and thus contribute to a stable process sequence. In this work, the influence of the surface properties of pure copper ribbons regarding the process reliability is investigated. Therefore, ribbons produced for a wire bonding process are thermally oxidised or mechanically roughened, and their optical properties are compared with a polished reference material. The sample ribbons are welded with a continuous wave fibre laser, and the mechanical properties of the resulting connection are investigated. Due to a more stable interaction of the laser radiation, a mechanically and electrically improved connection is expected.