BATTERY MANUFACTORING Fraunhofer develops new copper welding process for battery cells

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A consortium of scientists from the Fraunhofer Institute for Solar Energy Systems ISE and Smart Battery Solutions GmbH succeeded in replacing the steel connectors used to interconnect battery cells with copper during resistance projection welding. In doing so, the team demonstrated something that had long been considered impossible in the battery industry: Until now, battery manufacturers looking to switch to more powerful, copper-interconnected batteries had to replace their projection welding systems with laser welding systems.

Batteries consist of individual battery cells that are electrically connected to one another, currently mostly by welding steel onto them. Projection welding is a cost-effective, established process, but steel connectors are limited in their electrical conductivity. Replacing steel connectors with copper ones makes batteries lighter and thus more powerful.

“German battery manufacturers face the challenge of having to work with the battery cells they receive from their suppliers,” explains Dr. Achim Kraft, Head of the Module Technology Department at Fraunhofer ISE. “These cells are becoming larger and more efficient. Consequently, the steel connections must become increasingly thicker and heavier. It has therefore long been clear to the battery industry that, in the medium term, all interconnections should be based on copper.”

A research team at Fraunhofer ISE, in collaboration with the German battery manufacturer Smart Battery Solutions GmbH, has now succeeded in developing a process for use on projection welding systems, such as those commonly used in battery production today. “The copper does not need to be tinned or otherwise pretreated for this,” says Christian Schiller, researcher at Fraunhofer ISE and project manager of the research initiative. "And most importantly, battery manufacturers need not switch to laser welding systems in order to electrically connect the copper connectors in a battery module."

Smart Battery Solutions will now be the first battery manufacturer to introduce the new process on its production line. “The new batteries with copper connections will be a part of our UniPower product family,” says Monika Mertig at Smart Battery Solutions. “The fact that we only need to adapt our proven interconnection process for this and don’t have to completely replace it with new equipment makes the transition much easier for us. We at see this R&D success as a major opportunity for German battery manufacturers, many of which are small and medium-sized enterprises.”

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The research is being conducted as part of the project “BatCO₂tiv – Battery Interconnection: Automated, CO₂-Reducing, Collaborative. Subproject: Process Development and Evaluation for Projection Welding” and is funded by the German Federal Ministry for Economic Affairs and Energy (BMWE).

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