Laser welding of current collector foil stacks in battery production–mechanical properties of joints welded with a green high-power disk laser

Abstract

The qualification of production systems that enable reliable and stable production processes is a major challenge in manufacturing large-format lithium-ion batteries. During cell assembly, the electrode sheets of the anode and the cathode are stacked, and are electrically contacted by a welding process. It was shown that laser beam welding employing a beam source in the green wavelength range is a promising joining approach in terms of high productivity. Therefore, the influence of the process parameters, such as the laser power, the welding speed, the pulse frequency, and the pulse duration, on the weld seam quality was investigated. Particular emphasis was placed on the mechanical strength of the weld seam. Statistically planned experiments were used to determine feasible parameter sets for welding the most common current collectors of lithium-ion battery electrodes, copper (Cu), and aluminum (Al). The influence of the individual process parameters on the tensile shear force was evaluated. Stacks of 40 metal foils were welded with a thin metal sheet in lap joint configuration. Based on an analysis of the requirements for minimum mechanical seam strengths, this study confirms that laser beam welding using a green high-power disk source is an auspicious process for the internal contacting of lithium-ion batteries.

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

“…Da im Bereich der Batterieproduktion Spritzer zwingend zu vermeiden sind, wurde das Folienschweißen mit grüner und blauer Laserstrahlung verstärkt untersucht. Sowohl die Verbindung einzelner Folienlagen mit blauer Strahlung [11] als auch das Fügen von bis zu 40 Kupferfolien an einen Ableiter-Tab [12] resultierte in guten Naht eigenschaften. Vor allem die mechanischen Eigenschaften waren vielversprechend.…”

“…Vor dem Hintergrund dieser vielfältigen Vorteile für die Batterieproduktion und der steigenden Bedeutung von Stromkollektorfolien aus Aluminiumwerkstoffen ist es nötig, die bisher auftretenden Fehler zu eliminieren. 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].…”

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

“…[ 14 ] Another defect that occurs particularly with aluminum is foil stripping, which can be observed in the cross‐section. [ 15,16 ]…”

“…[14] Another defect that occurs particularly with aluminum is foil stripping, which can be observed in the cross-section. [15,16] In recent years, several studies have been conducted on the reliable welding of electrode stacks with different beam sources and process approaches. [15][16][17] Especially considering the modern beam sources in the visible wavelength spectrum compared to established NIR beam sources, reliable comparisons for the application in battery cell manufacturing are missing.…”

In-Depth Characterization of Laser-Welded Aluminum-and-Copper Dissimilar Joint for Electric Vehicle Battery Connections

“…Among these techniques, laser beam welding is considered one of the most promising methods for joining aluminum and copper, owing to its easy automation, high precision, small heat-affected zone, contactless process, high process speed, and possibility of easy welding of dissimilar metals. Compared with other joining techniques, good electrical and mechanical performances have been reported using laser welding [ 15 , 16 , 17 , 18 ]. However, laser welding remains challenging in the joining of dissimilar materials, owing to its high reflectivity, low solubility, and differences in the properties of the joining materials.…”