ON-THE-FLY-LASER-CUTTING IN BATTERY PRODUCTION

Increased precision and efficiency with data-based process optimization 

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AT A GLANCE - ON-THE-FLY CUTTING OF BATTERY FOIL 

 

  • Lasers offer an innovative solution for foil cutting: The precise processing of battery foil requires technologies that can reliably process sensitive materials. Conventional cutting processes are limited in continuous production, especially with complex geometries and high process speeds. The laser offers the necessary efficiency and flexibility for this.
  • Continuous production leads to complex cutting applications: An optimal design of the laser cutting process is crucial to ensure high precision and reliability. Multiple factors must be precisely coordinated, e.g., material speed, cutting geometries, and process stability. The use of safety margins and iterative tests often increases costs and time.
  • Data-based process analysis is key to efficient design: The Process Data Analyzer visualizes the signals of the scan system, such as mirror movement, focus position, or thermal load. This enables precise process design and reduces iterative tests and generous safety margins
  • Optimized cutting processes improve throughput and production stability: An optimized onthe-fly process reduces waste, shortens production times, and ensures flexible adaptation to changing requirements. Manufacturers benefit from shorter development times, optimized process control, and increased overall efficiency in production.

IN SEARCH OF INNOVATIVE CUTTING TECHNOLOGIES FOR BATTERY PRODUCTION

The precise cutting of battery foil is a key step in the battery production process, as the cut‘s quality directly impacts the final performance, safety, and service life of the battery cells. To meet the demand for ever lighter and more powerful batteries, modern production technologies such as laser cutting are increasingly coming into play. Lasers, in particular, offer several advantages over conventional cutting technologies: The laser beam enables very fine and clean cuts, and the process is wear-free, as no mechanical tools are used that could be subject to abrasion. Laser cutting is also flexible, thanks to modern laser deflection units. Different cutting geometries can be selected with a mouse click without replacing punches or cutting tools. Adaptations to a new active material that requires different process parameters (e.g., laser power) are also easy to implement. Additionally, laser cutting can be efficiently integrated into a continuous roll-to-roll process.

Despite this versatility, many battery manufacturers hesitate to switch to this technology. This is because the design of a laser cutting application, especially in continuous production processes, can be pretty complex. However, with good planning and experienced implementation partners, it is possible to realize even challenging laser-cutting projects. This allows battery manufacturers to prepare for future developments and meet the increasing demand for batteries, particularly for electric vehicles and energy storage solutions, also in the future.

Challenges in continuous foil cutting

Continuous cutting processes offer advantages for increasing the throughput of production systems. However, not all cutting methods are suitable for processing thin films. With punching processes, the belt must be operated in a stop-and-go mode, which is associated with high accelerations and, therefore, vibrations in the machine. Other mechanical cutting processes face challenges with more complex geometries. Mechanical methods are also subject to wear and tear, leading to quality fluctuations in production and requiring regular replacement of expensive cutting tools.

The cutting of the cathode poses a particular challenge for mechanical and laser cutting. This is due to the active materials used, which are harder and tend to form burrs. This can lead to safety risks. During this process step, it is essential that the separator film, which electrically separates the anode and cathode in the subsequent battery, is not damaged. As these polymer films are only approx. 10-20 µm thick and therefore easily damaged, the quality of the cut edges is essential, significantly when cutting the cathode. It is thus important to set the process parameters accurately and to ensure precise and reproducible deflection and focusing of the laser beam.

Another challenge for machine manufacturers is lateral inaccuracies in the foil feed. These can be caused by vibrations or uneven unwinding of the foil roll. Such inaccuracies result in the cut components not having the desired shape and size, leading to expensive production rejects.

The trend towards larger battery formats aggravates these challenges. Cylindrical cells (e.g., 46xx format), prismatic hard case cells (e.g., blade batteries), and pouch cells are affected. Cell formats change frequently due to new market requirements requiring flexible production solutions.

 


Figure 1: New electrode designs improve battery performance. Conventional batteries conduct electricity and heat by means of a single tab from the respective layer. The multi-tab design enables optimized current and heat transport. However, the new design also poses challenges, as up to 1000 tabs per second have to be cut to ensure the required production time of 1 cell per second.


LASER CUTTING ON-THE-FLY FOR CONTINUOUS PROCESSING OF COMPLEX GEOMETRIES

Laser cutting is an innovative solution for mastering the challenges of continuous processing of complex geometries. Modern pre-focusing beam deflection units, such as the RAYLASE AXIALSCAN FIBER RD-50, are specially developed for large processing fields. They offer the optimum combination of precision and speed required for demanding on-the-fly cutting applications. These systems can enable long separation cuts or cutting entire electrode sheets. A large free aperture enables small spot diameters of around 50 µm, resulting in clean cuts with a minimal heat-affected zone. The lightweight mirrors in the beam deflection units enable high scanning speeds and dynamic cutting movements, resulting in higher throughput in production. The sealed housing of the scanning system with defined interfaces and producing the deflection unit in a clean room ensure high power compatibility and reliability. All this ensures high process stability and consistent quality of the cut workpieces. 

In addition to long separating cuts and the cutting of electrode sheets, scanning systems are also used for notching. In this unique type of laser cutting, the electrode is not cut all the way through, but specific geometries are inserted into the continuously passing foil. These can be small flags or so-called foil tabs, for example, which later conduct the electrical current out of the electrode. Depending on individual requirements, f-theta-based 2-axis scanners with apertures of 15 mm to 30 mm are suitable for these notching processes. The smaller mirrors enable highly dynamic cuts, which benefits the process speed.


Figure 2: Continuous laser cutting if battery electrodes. Using lasers, the foil can already be cut during unwinding and a stop & go is avoided. Due to the resulting increase in efficiency, laser cutting is increasingly replacing the mechanical punching of electrodes. Depending on the application, different deflection units are used. Highly dynamic 2D deflection units are usually employed for laser notching. For larger cells, pre-focusing scan systems ensure the necessary small spot diameter.

Even though laser cutting offers many advantages for processing battery foil, it also presents challenges. For the mathematical design of an on-the-fly process on paper, many factors that are difficult to predict must be considered. This is why many processes use generous safety margins when designing the process. In addition, tests and trials of the design often require many iterations. This costs a lot of time and money and generates many rejects.
 

Requirements analysis is crucial for process design

Due to the complexity and potential cost of designing an on-the-fly process, it is vital to understand the given boundary conditions precisely. Depending on this, the other parameters can then be varied. 

There are three different starting scenarios for the design:

  • 1. The customer has clear requirements for the belt speed and wants to design the laser process accordingly. In this case, the productivity targets determine the belt speed. It must be determined whether continuous processing by several scanners is necessary and how many scanning systems are required to achieve the desired production rate.
  • 2. The customer knows the cutting speed from preliminary tests in the laser laboratory and would like to determine the resulting belt speed. Here, the maximum belt speed is determined, given a predefined quality.
  • 3. The customer would like to optimize an existing on-the-fly process: A precise analysis allows the process to be better adapted to the speed or quality requirements.

This results in priorities for the layout. In existing processes, for example, the number and the scanning system are usually set, and it is more of a question of mobilizing existing resources. A new design offers additional degrees of freedom by selecting the optimum deflection unit. 

Whether a new system or an optimization, the various requirements must be evaluated in terms of importance during the layout. This is because many parameters are interlinked and cannot be changed independently. For example, a large working field typically leads to a longer working distance and larger spot diameters. Here, finding the right compromise between the various parameters is essential. 

Process optimization based on real feedback signals

Even if a rough design is already possible using theoretical estimates, a precise evaluation and optimization of the process parameters is complex without actual data from the beam deflection unit. Productivity and cutting quality can only be reliably ensured with exact data on mirror movement, return times for path movement compensation, the positional accuracy of the z-focus during the cutting process, and the thermal load on the scanners.

The PROCESS-DATA-ANALYZER from RAYLASE offers an innovative solution by enabling a process layout based on real feedback signals. Visualizing the mirror movement and laser signals allows precise testing and design of the process. This helps to find the maximum speed at the required quality and to avoid quality losses due to defocusing or insufficient contour accuracy.

Figure 3: Process analysis and optimization based on feedback signals from the scanning system. Only the precise analysis of an on-the-fly application reveals whether the required accuracy can be achieved with the desired dynamics. Thanks to the RAYLASE PROCESS-DATA-ANALYZER (PDA), there is no need for extensive tests in the laboratory; the necessary data can be read back directly from the scan system. Additional information such as the current consumption or the temperature of the galvo motors can also be checked and estimates can be made for long-term operation.


Encoder signals correct for inaccurate material feed

NIn addition to the scan system‘s actual position values and status signals, real-time information about the roll-to-roll process is of great importance. For example, variations in the belt speed can lead to inaccuracies in the cutting result. In an on-the-fly process, the belt position is continuously measured using an encoder, and the control values are automatically adjusted. This always results in the desired cutting geometry, even if the film moves under the scanner at fluctuating speeds. 

Besides the movement of the foil due to unwinding and rewinding, the feed can also fluctuate laterally in the position of the foil and its height. As the battery foils must comply with precise dimensions, inaccuracies in the feed can affect the quality of the final battery. To prevent this, an additional edge detector can ensure that the lateral position is corrected. The position of the foil is read in via a second encoder input, such as on the RAYLASE SP-ICE-3 card, and the scan pattern is shifted accordingly in real-time. Inaccuracies in the z-position can also be corrected using an encoder, for example, by reading real-time values for the belt tension. This ensures high cutting accuracy even with imprecise feeding. 

Alternatively, the foil is cut at areas with a defined z-position, such as on a guide or a deflection roll. Here, the laser system must compensate for any curvatures in the processing field using an individual correction file, which can be created in the RAYLASE MULTIPOINT EDITOR software. 

For cutting geometries where a quasi-endless cut is required, RAYLASE offers a new feature called Endless -Marking-on-the-Fly (Endless MOTF). Here, the foil is cut without switching the laser on and off, and the resulting power fluctuations are avoided. This avoids stitching points in the edge, where there is an increased risk of defects. 

For the Endless-MOTF, the required path of the scanner mirrors is calculated in advance for a specific belt speed. Nevertheless, it is possible to react to fluctuations in the belt speed. This feature is particularly exciting for laser notching and promises significant quality improvements.
 

LASER CUTTING OFFERS FUTURE-PROOF SOLUTIONS FOR ELECTRODE PRODUCTION

Even though laser notching and cutting is still considered by many to be an innovative solution for specific needs, more and more battery manufacturers are switching to lasers in their production processes. There are many reasons for this. Laser cutting enables wear-free processing and prevents a loss of quality due to blunt blades. New tab designs can also be implemented easily without the need to adapt mechanical tools. 

The non-contact process of laser cutting is particularly advantageous when processing materials that are difficult to handle. For example, laser cutting offers an effective solution for the future production of lithium solid-state batteries with their soft and sticky film-like lithium metal layer. The laser will, therefore, become increasingly important in the future! 

In this context, application-optimized beam deflection units such as the AXIALSCAN FIBER series from RAYLASE and its established marking-on-the-fly technology play a decisive role by offering innovative solutions to existing challenges and further advancing efficiency and precision in battery foil production. Laser cutting is already an integral part of battery production today. And it will become even more widespread in the future, as it enables precise, flexible, and efficient production and thus meets the increasing demands of the industry.

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