Advanced laser technology provides the high-speed precision bonding necessary for cost-effective production of battery cells for electric vehicles.
The design and manufacture of larger-sized cylindrical batteries for electric vehicles promises several advantages for car manufacturers and consumers. For drivers, these include longer range, higher power, faster charging, longer battery cell life and better cold weather operation. Manufacturers can look forward to more efficient production and lower production costs.
What's so complicated about making batteries for electric vehicles?
Different manufacturers are working on a number of different designs for large-sized cylindrical batteries. Each design and workflow presents its own specific manufacturing challenges, especially when it comes to bonding processes. For example, some EV battery designs include current collectors and these must be joined to the cylinder of electroplating material with very precise weld depth control. This is necessary to avoid damage to the separators, which could subsequently lead to a short circuit inside the cell. Similarly, welding terminals to a collector requires careful control of penetration. It is particularly important to limit the amount of heat that is introduced into the battery during this operation, as it could melt or damage the polymer insulators.
Another joining process that has been used successfully in the past on smaller batteries to seal the caps is mechanical pressing. However, crimping is not well suited for larger cells and a new approach is needed.
What are the current requirements?
There are a number of welding processes used in battery manufacturing, again varying by manufacturer and design. However, the most demanding and sensitive of these all have certain requirements in common, including the need for:
- Minimum heat affected zone
- Precise control of the weld depth
- Elimination of material spatter
- High process speed, typically in the range of 200-500 mm/s
In addition, some important battery joining processes also require welding of dissimilar metals.
Each of these requirements has presented difficulties in the past, and in reality there is no single welding technology that can work well in all processes. Manufacturers have therefore looked for different solutions. These include green wavelength lasers for welding copper (to overcome the low absorption of this material by infrared sources) and non-laser methods such as ultrasonic welding for foil-to-tab joining.
Equip yourself with the right laser
Coherent has developed a new type of laser that has broader applications than anything before. This is possible because the technology provides an unprecedented level of control over how laser energy is delivered to the work surface - both in terms of spatial distribution and time.
A key innovation is Adjustable Ring Mode (ARM) technology - a fibre laser whose beam consists of a central point surrounded by another concentric ring of laser light, as opposed to the traditional single-point output. Most importantly, the output at the center and ring points can be independently controlled and even modulated. The graph shows how this approach provides tremendous flexibility in exactly how the laser energy is distributed during welding.
Figure: Basic power patterns of a focused point FL-ARM.
The advantage of ARM technology is that it allows very precise control of the melt dynamics. This allows for more consistent and controllable processing and virtually eliminates material spatter. This type of laser is particularly useful for copper welding because the circular beam can be used to preheat the material, which significantly increases its absorption of infrared light during subsequent processing. The high power density central beam ensures high absorption of the infrared laser beam by the copper. Together with the practical and cost advantages of fiber lasers, this makes the ARM fiber laser a very attractive alternative to green solid-state lasers for copper welding.
A single laser source type that can perform so many different tasks provides manufacturers with greater flexibility and cost-effectiveness. For example, the output from a single laser can be shared between multiple processes using beam switches. This streamlines and simplifies production. Using a common laser type at multiple points in the manufacturing process also reduces spare parts inventory and provides redundancy that helps minimize downtime for maintenance or repairs.
For more information on COHERENT HighLight ARM fiber lasers, visit optix.cz
