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How Digital Slitters Improve EV Fire Safety

An expert in battery cell slitting and calendering explains how electrode defects cause EV fires—and how digital tech prevents them.

Hiroshi Yamada, President of Maytech—a company specializing in slit consultation—launched a detailed examination of electric vehicle (EV) fires, and according to him, it traced the root cause back to the lithium-ion battery (LIB) manufacturing process. His findings revealed that most failures were linked to “burrs caused by poor cutting of electrode slits,” followed by “damage to the electrode caused by forcible sealing in a can of a specified size due to electrode thickness error.” Other contributing factors included foreign metal contamination and electrode misalignment. In this interview for Battery Technology, Yamada discusses how these defects arise, why they pose serious risks, and what battery manufacturers can do to prevent them—starting with better cutting practices.

What are the most common fire risks associated with electrode manufacturing?

Hiroshi Yamada, President of Maytech: First,  metal foreign matter is present in the electrode. This breaks through the separator and shorts the cathode and anode, creating a fire risk. It is possible to prevent this from entering from the outside during some electrode manufacturing processes. Still, the leading cause of fire risk is the metal foreign matter that occurs during the electrode slitting process.

Japanese battery manufacturers, who realized this fact early on, have actively introduced digital slitters and stabilized slitting quality with digital technology, and there have been no EV fire accidents in Japan to this day. However, it is no coincidence that the number of EV fires increased nearly 10 years ago when, due to demands for low prices from automakers’ demands to promote EV sales, most of the electrode slitting processes were replaced by cheaper, lower performance, and unstable quality slitters due to price prioritization when selecting battery manufacturing equipment.

How do slit defects and electrode thickness variations contribute to battery fire hazards?

Yamada: As mentioned above, metal foreign matter in slit defects can cause fires. Variations in electrode thickness can also cause slit defects and metal foreign matter in conventional slitters, which can lead to fires. In addition, when stacking the cathode and anode with a separator in between during the assembly process, there is a risk of fire if the stacking is misaligned due to electrode thickness variations and the cathode and anode come into contact. To explain the general meaning of “electrode thickness” in a little more detail, it can be interpreted in two ways:

When coating the electrodes, the basis weight and density are measured using radiation, and the physical thickness is measured after the calendaring process. The difference in measurement methods causes a contradiction between the physical thickness and the excess or deficiency of basis weight/density. Still, when the final calendar processing is used to make the physical thickness constant forcibly, the thickness, basis weight, and density become unstable.

How does digital technology help detect and prevent slit defects in electrode manufacturing? Can real-time monitoring and AI-driven analytics improve safety outcomes in electrode production?

Yamada: With the digital technology of the digital slitter, the optimal slitting conditions for the electrode and the amplitude range where defects do not occur can be grasped in advance as digital values, and the optimal conditions confirmed in advance can be digitally set during mass production to reproduce optimal quality easily. At the same time, the contact state of the upper and lower knives can be monitored in real time during operation, and good quality can be confirmed by checking that the amplitude is within the range confirmed in advance. If the range is exceeded, it can be determined that a slit defect has occurred.

By accumulating digitally confirmed data on the state of the upper and lower knives when slit defects occur during operation and analyzing it with AI, it is possible to understand the causes and countermeasures for slit defects under all conditions and issue commands to operate within that range at all times, thereby improving the safety of electrode manufacturing.

How are regulatory standards evolving to address fire risks in battery manufacturing?

Yamada: Battery manufacturers routinely use forced cleaners to forcibly remove burrs that occur, which certainly makes the surface look clean for a moment, but contamination occurs from the slits damaged by the cleaner, creating a dangerous situation. In addition, the inspection method for the slits is also a method that makes it easy to overlook defects. Automobile manufacturers are vaguely aware of the behind-the-scenes circumstances of such manufacturing processes, but they do not dare to point them out because if they do, it will lead to increased battery costs.

In other words, battery companies and automobile companies are not seriously addressing the regulatory standards that should be shared because they are considerate of each other’s industrial circumstances.

Are there case studies where digital solutions have successfully prevented fire hazards in electrode production?

Yamada: Because it is more expensive than the conventional type, there are few cases of its adoption, but we have received reports of dramatic quality improvements and stability compared to the conventional type through digital management. Although it cannot be said that it has directly helped prevent fire accidents, we believe it has contributed to it.

What advancements in digital technology do you foresee improving fire safety in the next five years?

Yamada: Progress expected in five years regarding slit defect countermeasures that lead to fire accidents could be the following: