Projects

Surfaces activation techniques in the production of lithium-ion cells

Sealing strip strength after curing in electrolyte – excellent adhesion after laser pre-processing
© Fraunhofer IWS Dresden

Sealing strip strength after curing in electrolyte – excellent adhesion after laser pre-processing

The joint project DeLiz (Production engineering demonstrator center for lithium-ion cells), funded by subsidies of the Federal Ministry for Research and Technology BMBF, addressed production engineering along the process chain of lithium-ion cell production. In this project, specific manufacturing technologies and methods, as well as machines and equipment required for their implementation, were refined, and new solution paradigms for low-cost, large-scale production were indicated.

Task

Contact tabs of aluminum conductor sealing areas must be pre-processed to guarantee a strong adhesive bond, tightness and long-term ageing resistance. Up to now, Zr fluoride treatment has been employed. In this technology, the chemical treatment of the substrate causes a complex zirconia (ZrO2) layer to form. This implies an improvement of the adhesive bond during and after sealing. Pre-investigations specifically show that long-term resistance is insufficient. Moreover, the pre-treated surfaces show heterogeneous ageing characteristics.

Solution

For this reason, in a DeLiz subproject, ways to pre-process the Al conductor sheets by laser were analyzed in detail. For comparison, the chromating (benchmark) and a simple cleaning by means of a solvent (used as a reference) were investigated.

Making use of laser beams, as a function of the adjusted laser wavelength, makes possible not only surface structuring, but also the formation of functional groups. Laser pre-processing means that both increases in strength in the bonded joint and enhanced ageing resistance can be expected. Last but not least, the integration capability in continuously working process lines provides a great potential for higher efficiency.

Results

Local laser surface treatment in the sealing zone contributed to a significant increase in the adhesive bond of the sealing tape. The long-term resistance achieved was outstanding and reached the quality level of yellow chromating. At the same time, in contrast to yellow chromating, laser pre-processing is regarded as a dry, selective and environmental- friendly, easy-to-automate method that can be integrated and scaled in production processes.

Research funding

This research and engineering project was funded by subsidies from the Federal Ministry for Research and Technology (BMBF) under the aegis of”SME Innovative: resource- and energy efficiency“ and supported by the Project Management Agency Karlsruhe (PTKA).