FACTORS to Consider
There are several factors to consider when designing a battery pack to manage the complex problem that is thermal runaway.
1. Potential Cell Failure Mechanisms
Different methods of cell failure (short-circuit, crushing, puncture, overheating, overcharging) result in different heating profiles
and ejecta material behaviors.
Latent Heat Solutions’ specialized materials are designed and tested to mitigate the unique dangers associated with each of these failure modes.
2. Cell Format, Chemistry, State of Charge, and Operating Temperatures
Many battery characteristics contribute to the behaviors associated with thermal runaway, and these must be accounted for in battery pack
design and testing.
The three common formats of Li-Ion batteries are cylindrical, pouch, and prismatic. Cylindrical batteries are one of the most popular formats and can be found in everything from power tools to medical devices, grid storage, robots, and aerial and ground based electric vehicles. Pouch and prismatic types are more commonly found in cell phones and other mobile electronics.
There are many different types of lithium-ion batteries that use different chemical compositions to produce charge, such as lithium iron phosphate (LFP), Nickel, Manganese, Cobalt Oxide (NMC) and Lithium Nickel Cobalt Aluminum Oxide (NCA). These different compositions all display different risk profiles during thermal runaway.
The state of charge represents how much electrical energy is contained in the battery at a given point in time. The more energy within the battery when a thermal runaway event occurs, the more damaging that event will be.
While most batteries are designed to operate within a range of temperatures, higher operating temperatures put batteries at an increased risk of experiencing propagation during a thermal runaway event. A battery pack’s thermal runaway protections should reflect the specific operating conditions of the electrical device which it powers.
3. Heat Management during Thermal Runaway
Many battery packs on the market today utilize various barrier materials to insulate battery cells and modules from one another. This can be useful for delaying thermal runaway propagation, but testing has demonstrated that rapid removal of large sums of heat from the system is critical to prevent total runaway propagation.
Many battery packs also utilize active heat removal systems, such as fans and heat pumps, during normal operations to maintain target operating temperatures. But these systems are unlikely to be sufficient for thermal runaway management even in combination with traditional, insulative barrier materials.
Latent Heat Solutions’ XTS PCM material rapidly absorbs and removes large quantities of thermal energy from the system during a runaway event, entirely preventing runaway propagation and extinguishing open flames triggered by the initial event.
4. Ejecta Management during Thermal Runaway
The elevated temperatures and internal pressures which a Li-Ion battery experiences during thermal runaway will inevitably result in the violent ejection of gasses and particulates into the larger battery pack.
A complete thermal runaway management solution must protect all sensitive battery pack components from the thermal and mechanical dangers posed by this ejecta.
Latent Heat Solutions has experience with a wide variety of ejecta barrier materials and can work with you to select and validate the most optimized solution for your unique battery pack specifications including weight, cost, etc.
5. Cell-to-Cell and Module-to-Module Spacing
In order to incorporate sufficient thermal runaway protections into a battery pack design, minimum cell-to-cell and module-to-module spacings must be observed. These spacings will vary based on cell type and battery pack operational specifications.
Our engineers are experienced in the determination of optimal spacings for a variety of thermal runaway mitigation strategies and are available for consultation.
There are many factors to consider regarding thermal runaway mitigation within battery packs. Understanding how individual battery cells fail and the dangers thermal runaway poses to nearby battery pack components is a crucial part of safe battery pack design.
Contact us to explore how Latent Heat Solutions can help with your next project. Whether you are looking to mitigate thermal runaway, facilitate faster charging and discharging, or increase battery cycle life, we can help.