And now the big questions raises in front of the big OEMs and EV experts are, why do lithium-ion batteries catch fire in electric scooters and electric cars, and what are the solutions? Exponent Energy (a pioneer in rapid charge battery technology) has explained in brief:
Table of Contents
Why do EV batteries catch fire?
Li-ion cells need to hit a few hundred degrees Celsius before a thermal runaway event can occur (the fires you see are the result of thermal runaway).
Most modern batteries automatically shut down around 45-55°C. And even if these safety precautions are not implemented, you cannot heat the battery to a few hundred degrees Celsius simply through ambient heat or the heat generated by the batteries.
(Sure, climate change is real and summers are getting hotter. But 100°C is not hot and the battery doesn’t generate that much heat in absolute terms compared to its thermal mass)
There are 3 metrics for every battery:
Hot summers and bad thermal management affect performance & life but don’t cause fires. It’s like using your phone on a hot day, after keeping it on the dashboard — it’s slow, hot, & shortens life. But they don’t affect safety!
99% of battery fires are due to short circuits leading to uncontrolled current. As a result, the cell’s temperature is up by a few hundred degrees Celsius, leading to thermal runaway.
Short circuits happen for three reasons:
1. Poor cell quality
2. Poor design of the battery (the way cells are connected & packaged)
3. Poor BMS (management of cells via sensing & software intelligence)
Cell quality matters
Poor cell quality can cause internal short-circuiting. This occurs when the anode and cathode are mistakenly joined internally due to construction irregularities, short-circuiting the regular current path. This leads to uncontrolled current, eventually. Becomes the reason for Thermal Runaway.
Cell packaging matters
Cell quality is not always the primary root cause of short-circuiting. Battery packaging design has a big impact on safety. Packaging refers to how you put the cells together, and how you electrically connect to them and hold them mechanically.
Poor BMS = Overcharging
Cells cycle between a lower threshold voltage and a higher threshold voltage, which roughly correlate to the 0% and 100% state of charge (SOC)
- LFP goes from 2.8V to 3.6V
- NMC goes from 2.8V to 4.2V
Overcharging NMC by even a minuscule 0.05V can drastically promote Lithium dendrite formation.
Overcharging: up and off
Overcharging causes cells to bulge, collide with each other, short-circuit and eventually lead to a fire. It’s dramatic and you don’t have to imagine it.
What is the solution? then
Well, throwing money and buying better cells doesn’t solve battery safety.
The problem is collectively shared between:
- Mechanical systems (we need better-designed packs)
- Electronics systems (we need accurate BMS sensing and impedance management)
- Software systems (we need deeper intelligence and reliable code that doesn’t crash)
And above all, a whole lot of testing.
TEST. TEST. TEST.
That’s why we move fast & break stuff in our labs before taking it out in the field.
We did the unthinkable: we exploded our battery pack (yes, deliberately). We pushed our pack to the limit to see when overcharging would lead to a battery fire.
The specific objective was to understand propagation (imagine 100s of cells sequentially undergoing thermal runaway, that’s propagation)
You need to know your limits to push it, equipped with all the safety gear of course.