Laser‐Based Joining of Electrode Stacks for Automated Large‐Scale Production of Li‐Ion Battery Cells

Abstract

Increasing productivity in cell manufacturing is a high priority to reduce manufacturing costs and meet the increasing global and national demand for lithium-ion batteries (LIBs) for electromobility. [1,2] In current cell manufacturing, the interconnection technology of the individual layers of cathodes and anodes is a particular challenge. The HoLiB project aims to develop an automated high-throughput production of LiB that links the sub-processes of fabrication, stack formation, and contacting, that is track-bound, and that has a continuous material flow. Linking the sub-processes promises to minimize non-value-added time components in buffers, reducing cycle time per assembled and stacked electrode to <0.1 s. The individual electrodes produced with a laser-based separation process are deposited in a magazine via a stacking wheel and welded there with a cell arrester tab. An ultrasonic welding process is usually used for this purpose, in which a tool applies contact pressure to the stack of foils and induces vibrations in the component by ultrasound in the kHz range. Friction at the interfaces causes the foils to be welded to each other and to the cell drain tab. When feeding electrode foils with a targeted cycle <0.1 s, the necessary mechanical contact to apply the process force and vibration is a constraint. [3,4] An alternative process for welding aluminum and copper is laser beam welding. For this, the laser beam is focused on the component surface to melt and weld the material. The feed motion and the positioning of the laser beam on the component can be achieved with precision by using a scanner. What is necessary for welding here is the absence of gaps between the joining partners, but no further pressure. [5] The electrical resistance of the resulting joined connection must be particularly low to ensure the functionality of the individual battery cell over a long period of time. In addition, the formation of weld spatter should be avoided, as this can lead to a short circuit in the cell. These requirements necessitate a comprehensive understanding of the process for laser-based contacting of battery electrode stacks. State of the ArtThe joining of electrode stacks for the production of LIB cells is currently mainly carried out using an ultrasonic welding process. Problematic for the process-safe joining of anode and cathode with this method are the high necessary forces and the vibrations and frequencies that act on the electrodes during the process. [6] These high energies can mechanically weaken or severely deform the electrodes. [7] Other limitations include tool wear and the need for accessibility to both sides of the joining partners.Laser beam welding, in contrast, is a noncontact joining technique that only requires accessibility on one side in the overlap configuration. Two different regimes are considered in laser

Laserstrahlschweißen in der Batteriezellproduktion/Laser beam welding in battery cell production- Contacting of thermally sensitive electrode stacks for advanced cell technologies

“…Die Rissbildung im Nahtnebenbereich wurde weder durch die Verwendung von Strahloszillation [6] noch durch den Einsatz eines Singlemode-Faserlasers [14] oder grüner Laserstrahlung [12] vollständig vermieden. Das Schweißen des Folienstapels in einem Multi-Überlappstoß zwischen zwei Blechen ist eine Maßnahme, die Rissbildung zu reduzieren [15]. Das Auftreten von Poren wurde bei dieser Prozessführung nicht vollständig verhindert [15].…”

“…Das Schweißen des Folienstapels in einem Multi-Überlappstoß zwischen zwei Blechen ist eine Maßnahme, die Rissbildung zu reduzieren [15]. Das Auftreten von Poren wurde bei dieser Prozessführung nicht vollständig verhindert [15].…”