How does thermal runaway spread?

A lithium-ion battery is made of multiple lithium-ion cells. Often, lithium-ion batteries are stored and transported near many other lithium-ion batteries. Because of this, it is important to know what will happen to nearby batteries if one cell enters thermal runaway.

Safety note

Safety scientists test batteries and other products in order to understand what happens when a product fails. These tests are always performed in controlled laboratory settings. This is important in order to be certain that the test results are valid and the scientists are safe as they perform the tests.

Do not attempt to recreate these tests yourself: instead, this pathway will take you to the lab virtually. If you are interested in performing similar tests yourself, consider pursuing a career as a safety scientist!

Extreme Test

Fire Exposure and Projectile Test

This test is known as the fire exposure and projectile test. It determines whether an exploding cell will spread fire on a large scale. Thermal runaway can result in fire and explosion. During the fire exposure test, if a cell explodes and the projectiles from the battery puncture the steel screen it sits on, that indicates that the cell has the capacity to spread fire on a large scale if it overheats.

Asset: The Projectile Test

Unfortunately, a lithium-ion cell experiencing thermal runaway can begin a chain reaction of thermal runaway among nearby lithium-ion cells.

For these reasons, it is crucial that product designers take care to design battery enclosures that not only protect batteries from damage, but also minimize thermal energy transfer between lithium-ion cells.

Factor 1: Shrapnel

When a lithium-ion cell goes through thermal runaway, it releases heat, fire, flammable vapor, and sometimes shrapnel: sharp pieces of the cell itself.

Shrapnel released from a lithium-ion cell can puncture nearby lithium-ion cells. That can damage those cells, causing internal short circuits that lead to thermal runaway. 

When an object near a battery heats up, the battery itself can overheat, too.

Lithium-ion cells have electrolytes that are highly flammable. When an electrolyte has evaporated and is exposed to heat of 80°C (176°F), that gas combusts.

Cells undergoing thermal runaway release thermal energy through convection, conduction, and radiation.

What’s more, being situated within a hot environment makes it harder for lithium-ion cells to lose heat.

This means that when one cell overheats, nearby cells are at risk of overheating, too.


Summarize your thoughts: How does thermal runaway spread?


Building a problem definition for thermal runaway

Different rechargeable devices need different numbers of cells in their battery. Imagine you are redesigning a one-child rechargeable ride-on car to accommodate two children, so you’ll need more lithium-ion battery cells in the car. What potential risks for thermal runaway spread do you need to consider as you design the new car?

Have you thought of a good solution idea? Continue through the pathway to learn more about the problem of thermal runaway so you can solve this engineering design challenge. 

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