X-ray inspection in the battery industry
December 20, 2022
Lithium-ion batteries are an integral part of our daily lives. You may not see one very often, but they are used in a variety of products, such as electric cars, cellphones and power tools. As the need for more lithium-ion batteries is increasing rapidly, giant production facilities (a.k.a Gigafactories) are being built around the globe to keep up with this demand. X-ray inspection is a crucial step in the production line of lithium-ion batteries, as faulty batteries can become very dangerous. By conducting a thorough inspection, one can ensure that the batteries will be safe to use, which is why X-ray inspection systems are such an important tool in the battery industry.
X-ray sources suited for battery inspection
Due to the wide variety of battery types and inspection needs, various resolutions and voltages are needed to meet the quality requirements. To confirm the production quality, a very high resolution is required to find the critical level of defects, ranging from below 5 μm to 130 μm depending on the type of battery and defect. The following Comet X-ray sources are widely used and serve the various needs in battery inspection:
The MesoFocus X-ray tube technology is one of our newest inventions. It’s available in two kV-classes depending on your throughput and resolution needs.
225 kV, 450 kV
In-line inspection, production environments
With the FXE, you’ll be able to see every little detail enabling advancements in cell design and chemistry. These open microfocus X-ray tubes are suited for offline analysis. It’s the perfect fit for a detailed inspection of the constituents of a battery cell.
160 kV, 190 kV, 225 kV
At-line inspection, lab environments
Cell types that can be inspected
Depending on the application, different battery cell types are needed. In our everyday life, we mostly deal with cylindrical cells. These are the long, round tube types of batteries we use for remotes and general household items. In bigger formats, and using lithium chemistry for higher energy density, cylindrical batteries are also used to power electric cars. Batteries used in cell phones and computers have another format adapted to their specific requirements, and so do those used in drones or RC racing cars.
For simplicity, three types of battery formats can be defined:
Cylindrical cells comprise of wound electrodes (also called jelly roll) in a can made from stainless steel and/or aluminum.
Unlike other battery formats, the shape of a cylindrical cell prevents swelling, an unwanted phenomenon in batteries. They are mainly used in power tools, medical instruments, everyday household items, e-bikes and electric vehicles.
Prismatic cells comprise of one or several jelly rolls stacked into a can with rectangular base.
Because of their rigid, rectangular shape, they are well suited for stacking multiple units in a battery module. They are usually bigger than cylindrical cells and therefore contain more energy per cell. These batteries are mainly used as energy storage and in electric cars.
Pouch cells comprise of stacked aligned electrodes that are sealed in insulating foil.
They are lightweight and mainly used in portable devices where they are installed in a housing such as cell phones and portable computers. Furthermore because of their versatility, pouch cells are also used in drones, RC racing cars, jump starters or in energy storage systems (ESS).
Why 100% inspection of batteries is crucial
Over the recent years, there have been multiple incidents of batteries catching fire or even exploding. It mostly happened with smartphones and other consumer electronics, but with the rise of electric mobility, cars are also affected. The batteries that malfunction usually had a defect that was not detected during or after production.
Because defects in battery production are so relevant for the safety of the consumers, 100% inspection (which means every single part gets inspected) is needed. There are four defects that occur most commonly, but with X-ray technology, no fault rests undetected.
Checking for this kind of defect is in many cases the most important. The anodes and cathodes must be uniform within certain boundaries. If they are outside of these boundaries, cell life is limited and the separator may be damaged.
In pouch cells, it’s very important that during winding/stacking, the sheets are aligned properly. If that’s not the case, bulging may occur, which can be very dangerous and even result in a battery catching fire.
Foreign particle inclusion
If foreign particles get inside a part of a battery, it can present a risk. Foreign particles can cause shorts or premature failure.
Cell assembly flaws
Defects can also occur during welding and sealing when assembling the cell. The batteries must be inspected for fractures, deformations, distortions, wetting and more.
Battery inspection in the production line
Depending on how fast a battery (part) should be inspected and what image quality is needed, there are different inspection methods. Generally speaking, setting up a production inspection is finding the sweet spot between inspection speed and image quality for maximal throughput and failure detection.
2D imaging with line scanners
This inspection method is the fastest, because the production line moves continuously while X-ray images get taken. The image quality is in many cases sufficient for effective anode overhang inspection.
Classic 2D imaging
Classic 2D imaging is by far most often used because it’s still very fast and provides good quality images. To get a higher resolution, the conveyor belt stops for a short amount of time when the X-ray image is taken.
To get a 3D image quickly, several off-angle images are taken of a battery (part) and thus, its volume is reconstructed.
Full 3D CT
Here, the part is truly inspected from all 360°. Full 3D CT provides the best images but also takes the longest.
Why every battery production facility needs X-ray inspection
Due to the complexity of batteries and the variety of defects they can contain, a 100% inspection is a requirement. X-ray inspection is the only technique that enables to see inside of the produced parts without altering its properties. Newest non-destructive X-ray technology allows for a 100% inspection, providing data and images of all parts of the battery cell. The main purpose of implementing X-ray inspection in the production line is to make batteries safe.
Want to know more?
To get more information and to find out what best suits your needs, get in touch with your local sales representative.
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