Fraunhofer Institute for Solar Energy Systems ISEThis subproject of “BatCO₂tiv” focuses on the development and evaluation of automated projection welding processes for connecting battery cells. The aim is to establish efficient, collaborative manufacturing processes that increase production volumes, reduce CO₂ emissions, and improve the quality of battery storage systems.
Battery Interconnection: Automated, CO₂-Reducing, Collaborative
BatCO₂tiv – Subproject: Process development and process evaluation for projection welding
The automatic welding machine with robot and inverter enables precise short-time resistance projection welding of battery cells.
Initial Situation
Batteries are key components for the energy transition and electromobility, but they require reliable, fast, and economical interconnection processes. Current challenges in battery storage production include short cycle times, flexible manufacturing structures, process monitoring, and maintaining local value creation. Manual or inefficient joining techniques limit production volumes, increase costs and emissions, and complicate inline quality assurance.
Objective
The objective of the subproject is to set up a multi-mix split line and increase production capacity through the development and evaluation of a process for short-time resistance projection welding in an automated welding machine. Specifically, design rules for cell connectors and cell holders are to be developed, cycle times per welding point reduced to <0.6 s, the service life of the welding electrodes increased, and non-invasive inline methods for characterization and process monitoring established. By accelerating and optimizing the manufacturing process, CO₂ emissions during production are to be reduced, thereby also reducing the CO₂ footprint for last-mile delivery products such as e-scooters, sharing systems, and e-bikes. This contributes to the implementation of the energy transition and promotes sustainable energy storage.
Approach
The solution involves integrating collaborative robots for human-machine interaction and developing intelligent process control to optimize welding parameters and electrode service life. A significant reduction in process time is crucial for damage-free connection of the battery cells. Unlike conventional projection resistance welding, the low heat input during short-time resistance projection welding does not result in weld lenses, but rather causes the material to sublimate. For quality control, criteria appropriate to the sublimation mechanism must be applied. Design rules for pack design, cell connectors, and holders enable machine-friendly processing. At the same time, non-invasive measurement methods for the inline evaluation of weld points are being validated and correlated with the process parameters to enable automated release or rejection.
Results
The subproject delivers validated processes for cost-effective, automated short-time resistance projection welding of copper, with a proven reduction in welding time per battery cell to less than 0.6 seconds and improved electrode service life through intelligent process control. Design rules for cell connectors and cell holders are being developed, as well as a pack design that ensures uniform current distribution to the parallel-connected battery cells. Evaluated non-invasive inline methods and correlated process/quality data enable reliable process monitoring. Overall, this results in a significant increase in production capacity for the UniPower family, lower CO₂ emissions and costs per unit, while improving performance and thus strengthening industrial value creation in Germany.
Micro-computed tomography of a copper connector that was joined to the battery cell housing by short-time resistance projection welding.
Funding
The »BatCO₂tiv« project is funded by the Federal Ministry for Economic Affairs and Energy (BMWE).
