Analysis of photodiode signals for monitoring the laser beam welding process of cell-internal contacts in lithium-ion batteries

Sophie Grabmann, Felix Harst, Christian Bernauer, Tony Weiss, Michael F. Zaeh

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

A major challenge in producing lithium-ion battery cells is establishing reliable and stable manufacturing processes. Cell-internal contacting is one step in the battery cell production chain in which the uncoated sections of the current collector foils of the individual electrodes in the cell stack are electrically connected by a joining process. Laser-welding technologies open up new possibilities for improving the battery cell design. However, the industrial use of laser beam welding for cell-internal contacting has so far been limited. Numerous process parameters influence the quality of the resulting welds, necessitating the need for seam quality monitoring. Currently, weld inspection is performed offline and mainly manually, making the evaluation highly dependent on individual inspectors. Implementing inline process monitoring has the potential to reduce time-consuming quality checks after the joining process and to increase the objectivity of the seam evaluation. Photodiode sensors are a widely used and cost-effective option for process monitoring in laser beam welding. The application for cell-internal contacting has yet to be investigated. Therefore, the objective of this study was to assess the applicability of photodiode sensors for monitoring the welding of copper foil stacks as used in lithium-ion batteries. A signal analysis was performed to understand the effects of geometric setup variations on the detected signal characteristics. The photodiode signals for bead-on plate welding of a single copper sheet and for joining foil stacks with different surface roughnesses were compared. The results revealed a substantial dependence of the resulting energy input into the workpiece on the specific sample configuration. In addition, the information value of the signals was investigated with respect to the detection of welding defects, such as part-to-part gaps and electrode coating residues. The presented results pave the way for a first-time-right production through fully integrated process monitoring in laser-based cell-internal contacting.

Original languageEnglish
Article number110730
JournalOptics and Laser Technology
Volume175
DOIs
StatePublished - Aug 2024

Keywords

  • Battery production
  • Cell-internal joining
  • Electric mobility
  • Laser beam welding
  • Photodiodes
  • Process monitoring

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