(41g) Application of HAZOP Methodology to Thermal Hazard Identification for Lithium-Ion Battery Manufacturing Processes

Occupational and machine safety hazards are well defined for lithium-ion battery manufacturing lines; however, thermal hazard identification and mitigation is commonly overlooked. A Hazard and Operability Study (HAZOP) can be an effective approach in identifying and managing thermal risk posed by lithium-ion battery manufacturing processes if the methodology is adjusted to account for the differences in design and operation of a mechanical manufacturing process.

The phrase “Keep it in the pipes” is one of the most well-known process safety guidelines in industry. It’s commonly said that the hazard is greatly reduced when the process is contained. While this guideline applies perfectly for liquid, vapor, and combustible dust processes, say this to a battery manufacturing engineer and they will respond with a blank stare. So, what failures does a battery manufacturing process focus on when attempting to identify thermal hazards? The answer starts with collecting cell and battery failure data from product abuse testing or historical failure rate databases. Both options provide an understanding of the types of failures that result in thermal hazards. Data from product testing is the most reliable source as it’s the most accurate representation of failure modes specific to the product design. However, historical failure rate data from a representative product design (e.g., similar form factor, state of charge, etc.) can be utilized when testing data is unavailable. Additionally, failures resulting in thermal hazards must be identified for the intermediate battery configurations along the manufacturing process, such as: individual cell level, at the bandolier and array level, at the module level before battery enclosure, and at the completed product level.

The identified failure modes can then be utilized to define a set of deviations applicable to the manufacturing process. Low/no flow may become dropping the cell/battery, high pressure may become piercing or puncturing the product, phase change may become shorting of the product, and temperature deviations likely remain unchanged. Where most HAZOPs for liquid / vapor processes tend to utilize human factors and facility siting checklists, human interaction with the manufacturing step should be reviewed in detailed (while ensuring that the HAZOP does not become a traditional machine risk assessment) for personnel related thermal hazards. As with any HAZOP, the methodical approach of reviewing each inlet and outfeed from each discreet manufacturing step is applied.

Another adjustment to the traditional HAZOP process lies in the definition of “tolerable risk.” Unlike A traditional HAZOP, battery manufacturing thermal HAZOPs need to account for much higher frequency failures that may need to be defined by cycle time or operating time while keeping the range of consequences consistent with those utilized for traditional HAZOPs. Personnel presence is another factor that should not be discounted in risk ranking; a factor that many traditional processes may lean on to define a lower actualized risk. While much of the li-ion battery manufacturing process is automated, many personnel remain in the manufacturing space performing maintenance, troubleshooting the process, or managing non-conforming products rejected from the process. Therefore, it is likely under conservative to assume no personnel presence in battery manufacturing spaces.

Application of the HAZOP methodology to battery manufacturing brings insight into thermal risk and required or existing thermal mitigation systems. It allows manufacturing teams to identify thermal safety critical instrumentation and equipment beyond the traditional machine safety systems commonly associated with mechanical manufacturing processes (e.g., e-stops, proximity sensors, etc.). Ultimately, the HAZOP methodology has a surprisingly strong application to identification and management of thermal hazards posed by lithium-ion battery manufacturing processes but needs to adapt to the difference in technology and operation.