Process stability in welding of battery cells with ultrasonics
As one of the world's leading developers of customer-specific lithium-ion battery cells, CUSTOMCELLS® pursues the lowest possible reject rate in battery production with maximum process reliability. For the welding of its applications, the development and production company relies on ultrasonic technology in one of their production lines. The ultrasonic welding systems from Herrmann Ultraschall used there minimized the reject rate and optimized production efficiency.
The newly developed battery cell from CUSTOMCELLS® uses tabs that are significantly smaller than what is typically used in the industry. To ensure reliable welding with a minimum reject rate and maximum process reliability, the welding tool must be adapted to the respective size.
The challenge for Herrmann was to develop a suitable sonotrode and to determine the right welding parameters in the shortest possible time so that safe and reliable production of the battery cell could begin as quickly as possible.
Optimization of the reject rate
In the associated production line, CUSTOMCELLS® performs the pre-welding and main welding on pouch cells. The first step in the pre-welding process is to pre-weld the individual layers of copper foil for the anode and the individual layers of aluminum foil for the cathode. In a second step, the main welding, the so-called tabs are welded to the cathode and anode.
Both pre-welding and main welding require strong, material-to-material connections to ensure the functionality of the battery cells. If individual foil layers are not completely joined together or if there are tears in the foil, which are only a few microns thick, this can lead to rejects and then to the disposal of the entire cell.
The ultrasonic welding machines from Herrmann provide a stable process for these connections. The HiS VARIO B 20 kHz systems have been specially developed for welding battery applications with multilayer foils. They reduce production waste and production costs.
Special battery design as a challenge
The special feature of the battery cell developed by CUSTOMCELLS® is the size of the tabs. They are significantly smaller than what is typically used in the industry. In order to ensure a reliable connection between the tab and the anode or cathode, the sonotrodes of the ultrasonic welding machines were adapted to the respective size.
Thanks to ongoing research and development work, Herrmann Ultraschall was able to draw on an existing, special sonotrode design right at the start of the project. This guaranteed a reliable welding process for the CUSTOMCELLS® battery application. After a short time, the appropriate welding parameters were also evaluated in the ultrasonic laboratory. The changeover to Herrmann welding systems could be implemented with virtually no downtime for production.
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Both Herrmann welding systems are permanently used for the welding of cell tabs at CUSTOMCELLS®. Within the scope of series production, the ultrasonic welding systems will be integrated into the automated production line in a next step. Ongoing consulting as well as the development of suitable welding solutions by Herrmann Ultraschall enable a smooth process integration.
With Herrmann Ultraschall we share a passion for reliable connections
"With Herrmann Ultraschall we have found a reliable partner for the safe welding of our lithium-ion cells. We are very much satisfied with the Hermann Ultraschall systems and have been able to permanently improve our product quality. We can recommend Hermann Ultraschall without any reservation."
Christian Zender, COO Customcells Tübingen GmbH
Only by using ultrasonic welding systems that meet the demand and requirements, can reject rates in battery production be kept permanently at a low level. Flexible service by the ultrasonic partner is important for the success of a welding project in order to be able to react immediately to changes in the production process if necessary. The interaction of suitable welding solutions and good service forms the basis for safe and efficient production of battery applications with ultrasonics.
Images: © CUSTOMCELLS® - www.customcells.org
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