If you’re reading this, there’s a strong chance that you have some misconceptions about thermal runaway.
Why do I say that?
Every day, I speak with engineers and technicians in many different industries, including aerospace, automotive, robotics, and more. Quite often in those conversations, I find that they hold one of the many common misunderstandings about thermal runaway and propagation—and most of the time, it’s impacting the safety and integrity of their products.
It’s important to understand that “No Propagation” isn’t a complete solution, and there’s the potential for catastrophic loss if you don’t have the right solutions in place.
Keep reading to learn more about these common misconceptions and the need for comprehensive flame management strategies beyond “No Propagation.”
In flame control, "No Propagation" means that failures in battery systems do not spread from one component to another.
With lithium-ion batteries, localized issues such as a short circuit or thermal runaway in one cell can sometimes spread to adjacent cells or the overall system if not properly contained. This is why you often hear about why battery design must allow for higher safety and reliability levels, minimizing the risk of widespread failure that could arise from a single point of failure.
Thermal runaway solutions ensure containment through the use of flame-retardant materials, fire barriers, and strict safety protocols to make sure that real-world applications for Li-ion batteries are safe and effective. This is often done with phase change materials, which can manage and convert heat by transferring water to gas, for example.
When thermal runaway isn’t managed, latent damage in battery packs can go unnoticed until it leads to failure. That’s why “No Propagation” doesn’t tell the whole story.
Overheated Li-ion batteries can be dangerous, especially considering how often they are used in everyday devices like e-bikes, scooters, and even laptops. In fact, 49% of e-bike owners are unaware that there are even safety standards for lithium-ion batteries.
Every year, there are thousands of fires across the US that are started by Li-ion batteries, so it’s critical that you have proper thermal runaway solutions within your products.
So, how are batteries tested to ensure that they will perform properly in the real world? The most effective way is to run puncture tests on Li-ion batteries to determine how loss of integrity might impact the surrounding materials.
The engineers at Latent Heat Solutions ran one test (video below), under these conditions:
Puncture to short the cell internally, causing a rapid and self-sustaining temperature increase (> 20 deg C per min) until the onset temperature ( >120 deg C) causes venting, fire, and an explosive thermal event of the trigger cell. The trigger cell temperature peaked above 400 deg C.
Adjacent cell temperatures are monitored to ensure external temperatures of each adjacent cell does not exceed 100 deg C.
Visual monitoring for any secondary combustion/flames persisting after the initial trigger event.
Many times when we run these tests, even when an initial thermal runaway event is triggered, propagation gets delayed by up to 15 minutes. Depending on how the battery pack is constructed, it can continue to burn internally without being directly observed during testing.
That’s why relying on flame-retardant materials within the battery pack is not sufficient to guarantee against propagation at a later time. You need flame suppression—and that’s an important distinction.
Rather than targeting progagation prevents, our solutions at LHS Materials actively suppress flames while being able to limit the effects of thermal runaway.
What’s the difference?
Flame-retardant materials are designed to only stop themselves from burning. They are not designed to extinguish flames if another material or component is already in flames, which is what happens under thermal runaway.
Flame suppression materials, on the other hand, are rated under test conditions that are more extreme than typical thermal runaway. They are designed not only to extinguish flames, but to prevent them from spreading and damaging components around the battery pack or even the product itself.
So, when you see headlines about a home-destroying fire that starts with an e-bike battery fire, you can assume that there were no flame suppression materials installed in the battery pack.
Scenarios like this are why your Li-ion batteries need rigorous testing with the help of a reliable thermal runaway expert. When tests are done without the proper expertise—and I’m speaking from experience—they don’t have the complete understanding of the physics and accounting for all variables.
To ensure that you’ve got the right flame suppression material to prevent thermal runaway in your battery pack, talk to an experienced engineer on our team. We’ll help you maintain battery safety and effectiveness through the entire life of your products.