Laser Welding The Alternative To Ultrasonic Wire Bonding
When making interconnections in battery modules, laser welding is faster than traditional wire bonding. For cylindrical cells, busbars can even be welded directly to the cells instead of connected via wires, diminishing by half the number of welds in the module. Single-mode fiber lasers also provide an excellent and controlled weld penetration with minimal spatter and reduced heat.
Whereas ultrasonic welding systems use sonotrodes specifically designed for each application and limited to simple shapes, the Laserax welding systems can be adjusted on the fly to create various welding patterns and sizes.
Overview of battery welding applications
- Materials: Copper, nickel, aluminum, and stainless steel, dissimilar metals
- Types of cells: Cylindrical and prismatic
- Battery components: Tabs, terminals, foils, busbars, cell cases, safety vents, cover plates
The Fastest Welding Process
When making cell-to-busbar connections, ultrasonic wire bonding typically takes between 500-1000ms per weld. Laser welding is much faster because it involves fewer, smoother mechanical movements: only ultra-fast mirrors located in the laser head need to be moved to position the laser beam. This drastically reduces the positioning time for each weld. When integrated with our robots, the average welding time including mechanical movements between cells can reach values under 100ms per cell.
| Cell Type | Busbar Thickness | Cell Thickness | Weld Type | Weld Dimension | Laser Power | Resistivity (µΩ) | Shear Test (N) | Time (ms) | Depth of Penetration (µm) |
|---|---|---|---|---|---|---|---|---|---|
| 21700 cylindrical | 250 µm Al 1100 | 500 µm nickel-plated steel | Positive Pole | Spiral 2.4 mm | 450W | 5 | 195 | 40 | 100-150 |
| 21700 cylindrical | 250 µm Al 1100 | 300 µm nickel-plated steel | Negative pole | S shape 3.6 x 0.5 mm | 450W | 5 | 150 | 40 | 100-150 |
| 4680 cylindrical | 600 µm Al 1050 | 0.8 mm Al 1100 | Positive Pole | Spiral 4 mm | 750W | 4 | 650 | 85 | 100-150 |
| 4680 cylindrical | 600 µm Al 1050 | 0.8 µm nickel-plated steel | Negative pole | Spiral 4 mm | 750W | 1.2 | 800 | 85 | 100-150 |
| Prismatic | 2.32 mm Al | 1.62 mm Al | Positive Pole | Spiral 7 x 5mm | 2000W | 3.5 | 2200 | 283 | 300-500 |
| Prismatic | 2.32 mm Al | 1.62 mm nickel-plated copper | Negative pole | Spiral 7 x 5mm | 2000W | 4 | 2500 | 236 | 300-500 |
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Cross-section view of busbar laser welding - Negative tab (Microscope image)
- 250 um Al on 300 um nickel-plated steel
- Shape: S Shape
- Pitch: 200 um
- Dimensions: 3.6 x 0.5 mm
- Speed: 500 mm/s
- No assist gaz
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Cross-section view of busbar laser welding - Negative tab (Microscope image)
- 600 um Al on 500 um nickel-plated steel
- Shape: Spiral
- Pitch: 200 um
- Dimensions: 4mm
- Speed: 700 mm/s
- No assist gaz
-
Cross-section view of busbar laser welding (SEM image)
- 2.32 mm Al on 1.62 mm Al
- Speed: 230 mm/s
- 51/min Argon assist gaz
Real-time Weld Monitoring To Detect Bad Welds
Laser Weld Monitoring (LWM) devices can be used to detect bad welds in real time during laser welding. This ensures that every single weld in the battery is good, and that defective ones are reworked right away.
Optical sensors installed in the laser use reflected and emitted radiation from the weld to determine if the weld is good. They can detect different types of weld defects such as gap or contamination.
- Each row represents a wavelength that’s tracked by the LWM (plasma, heat, laser back reflection)
- The blue line in each row represents the radiated reflected light signals tracked in real time for the current weld
- The two green lines in each row represent the ± acceptance limits for the wavelength at any given time
- Blue lines that extend beyond the green acceptance limits for a certain period of time can be associated with weld defects
Revolutionizing Efficiency
Because of our faster welding speed, a single laser welding machine can easily work like 10 ultrasonic wire bonders. This minimizes the number of machines needed in production facilities, allowing you to:
- Save square footage
- Save energy
- Reduce maintenance
Cylindrical Cells: From 4 Welds To 2 Welds
Whereas ultrasonic wire bonding typically requires 4 welds per cell, laser welding only needs 2. This provides several benefits:
- A larger contact area
- Half as many potential failure points
- One weld carries all the current (higher current per weld)
- Less mechanical stress transferred to the module
- Smaller resistance (lower heat & electrical loss)
- Better current distribution
- Better heat transfer from cells to busbar conductors
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2 welds per cell (customizable weld pattern)
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Ultrasonic wirebonding with 2 wires per cell (over and under) and 2 small welds
Laserax Benefits
- Fastest lasers on the market with unmatched scanning speed
- Turnkey solutions (Class 1 certified laser safety, fume extraction, vision, automation, etc.)
- Optical configuration that prevents overheating
- Quickly configuration for different battery assemblies (automatic change in the laser configuration)
- Minimal heat affected zone (HAZ)
Client Testimonial
For our project to laser weld cylindrical 21700 cells modules back in 2022, NorthVolt was seeking a fast and flexible machine to accommodate our needs for high throughput as well as continuous evolution of our product design. The Laserax technology seemed to be the perfect fit for our need, allowing speed and flexibility with their robotic dynamic clamping while maintaining high welding quality. Laserax supported us from early weld process development all the way to product design adaptation. Now that the machine is delivered and is performing very well, we are glad we trusted Laserax who did deliver to their promise. They were notonly a supplier but a true partner for NorthVolt and tremendously helped our company achieve its goals.
— Karl Fahlström — Manager at Technology Development, NorthVolt Systems AB
