The individual cells are connected to form modules or packs by so-called busbar welding. A live rail is designated as the busbar. Prismatic cells or cell modules can be combined with like materials (Al/Al or Cu/Cu) as well as with mixed combinations (for example, Al/Cu). It is important that the combinations are mechanically solid as they are subjected to vibrations and heat in the car. At the same time, an electrical connection with the least resistance must be ensured long-term. During the welding process, as little spatter as possible must be generated. Reproducibility, minimum heat input and defined welding depths also play an important role.
The challenge: an economic production of high-performance lithium-ion batteries with process reliability for electromobility
In the construction of electric cars today, almost only electrolyte-supported lithium-ion batteries are used. Up to now, alternative combinations such as solid-state batteries or other chemical components have not yet reached the industrial maturity required.
Lithium-ion battery production is a very elaborate and sensitive process incurring very high material and energy costs. For this reason, the manufacturing process must be very efficient with high batch numbers and minimum rejects. The top objective of the battery sector is to achieve a high gravimetric energy density (Wh/kg) and therefore also high milage (range) which is directly reflected in the range of electric cars. Furthermore, the aim is to develop and build battery cells which comply with the high demands of the automobile industry in terms of safety, performance and service life. The laser as a tool offers unsurpassed benefits in this respect in questions of process reliability, precision and efficiency.
Different cell types, the same applications
Three types or formats of lithium-ion batteries are used in electromobility. The functioning principle is essentially the same in all types. The main differences are in the design, requirements and materials used.
Where is the laser used within the manufacturing process for battery cells?
Selected key applications within the process chain using the prismatic cell as an example
There are two application areas when cutting battery foils. On the one hand - "slitting": continuous lengthwise cutting or separation of the mother coil (electrode foil coated on one or both sides). It is cut into several subcoils (parts). The laser is in a fixed position, the foil runs continuously through the laser beam from roll to roll.
The second application area is contour cutting of the coated electrode foil. In this case, electrodes (anodes/cathodes) are cut from the coil in the required shape and quantity. In combination with scanner optics and moving axes or further lasers to increase the scanning area, the laser cuts the electrode foil to the desired shape. During contour cutting, the speed is above 1m/s. The foil thickness (foil and two-sided coating with active material) is between 100 and 250 µm. For both applications, TRUMPF lasers satisfy the high demands of battery manufacturers in terms of cutting speed, heat-affected zone, burr formation as well as particle or spatter formation.
The active material on the electrode foil must be dried after the recoating process. Industrial VCSEL heating systems can take over this step, for beam sources based on VCSEL arrays are able to very quickly and selectively heat large surfaces with directed wavelength-selective infrared radiation. The reduction in the drying path decreases the footprint of the drying ovens significantly. The solution also increases the processing speed and saves costs and energy.
Electrode foils are very thin copper and aluminum foils (thickness of 6-14µm) which as carrier foils serve as anode and cathode for the active material. The foils are welded together as stacks or coils to the respective contact surfaces (30-60 layers) to form one anode and cathode each. One-sided access to the workpiece is ensured with our lasers. This means that stacks with over 60 foils can be reliably welded and with a very minimum of spatter.
TRUMPF lasers seal the prismatic battery housing (can), fitted with the electrode pack, which generally consists of a deep-drawn battery housing (wall thickness: 0.6 - 0.8 mm), to the 1.0 – 1.8 mm housing cover (cap) so that it is media-tight – without pores, cracks or unwanted seam buckling. The welding process with axis-guided fixed optics with welding speeds of 10-12m/min is state-of-the-art. The TRUMPF BrightLine Weld technology provides spatter-free welding and the utmost process stability. A highly dynamic solution with welding speeds over 25m/min is also possible in combination with PFO scanner optics and sensor system.
Battery modules consist of several interconnected battery cells combined to one power unit in a module housing. Depending on the cell format used, the module housing fulfils a somewhat different function. Aluminum alloys are generally used here, sometimes stainless steels as well, which have a medium to high tensile strength. Our high-power IR lasers weld them with maximum stability and with no cracks or distortion.
There is a multitude of applications for battery cells and modules for cleaning and structuring with lasers. This starts with electrodes, where the active material is partially removed or structured and ends with battery cell or module housings, where surfaces are roughened for better adhesion, or insulating paint, acid marks and oxide films are removed. Our entire service portfolio of short and ultrashort pulse lasers is used for these processes.
TRUMPF marking lasers mark the sensitive battery cells and their housings with precision and absolutely no contact. This means, for example, that all components can be marked with the Black Marking process, with very high contrast, good legibility and maximum corrosion resistance. This durability is also the prerequisite for the legally required traceability and documentation of the components.
- Welding soft connectors
- Welding seal pins
- Welding burst plates
- Welding terminals
- Tab welding of pouch cells
- Pre-welding (tacking) of can-caps
- Welding charge state sensors
- Welding Cu-Al connections
TRUMPF as your partner
Whether it is a laser with a green wavelength for welding Cu materials, beam formation (BrightLine Weld) for welding aluminum and copper with no spatter or pores, or special sensor systems for quality assurance and process monitoring – TRUMPF offers countless innovative manufacturing solutions for the production of battery cells. Benefit from our technology packages with a wide selection of beam sources, optics, sensor systems and application expertise.
The TRUMPF BrightLine Weld technology is the key to low-spatter laser welding of busbars, soft connectors, can-caps or module housings with high power IR lasers. Furthermore, our TruDisk lasers with green wavelength are predestined for highly reflective materials such as copper, for example – up to 2kW continuous wave or pulsed up to 400 W average power. Defined and constant welding depths can be executed and provide reproducible processes. During heat conduction welding, you also benefit from minimum heat input into the workpiece. Our sensor systems (VisionLine, OCT and welding depth monitoring) were specially developed for fully automated and highly productive manufacturing. This means you can always rely on complete documentation and traceability.
Our TruDisk laser design achieves optimum laser utilization in terms of time sharing and redundancy operation with several laser outputs for each laser. Furthermore, you benefit from consistent laser power on the workpiece thanks to our laser power control.
We see ourselves as your application consultant and enabler for new production opportunities. Benefit from our consolidated industrial expertise and our decades of experience as a laser pioneer.
Take advantage of a consultation by our experts and our worldwide service network. Whether you need service or application development – we are where you are. For example, TRUMPF experts and algorithms monitor your lasers to ensure anticipatory maintenance, especially for sensitive and large-scale production lines, with the Condition Monitoring Service.
The TRUMPF Laser Applications Center in Ditzingen
Many cases, one worthwhile visit
Spanning an area of over 4,000 m², the TRUMPF Laser Applications Center in Ditzingen is one of the largest laser application centers in the world. Using your actual component, our application specialists and industry experts will support you during application development and optimization in the Laser Applications Center – with our extensive portfolio of versatile laser processing systems.