Most lithium-ion battery fires and explosions come down to a problem of short circuiting. This happens when the plastic separator fails and lets the anode and cathode touch. And once those two get together, the battery starts to overheat. There are a number of reasons that the separator can fail:
To understand why lithium-ion batteries sometimes fail, you need to know what’s going on under the hood. Inside every lithium-ion battery, there are two electrodes—the positively charged cathode and the negatively charged anode—separated by a thin sheet of “microperferated” plastic that keeps the two electrodes from touching.
Why do batteries explode? The exploding batteries on the Samsung Galaxy Note 7 have caused a huge recall and a red face for the South Korean smartphone giants. Lithium ion batteries have two electrodes sandwiching a layer of flammable organic solvent electrolyte between them.
The lithium-ion battery from a Japan Airlines Boeing 787 that caught fire in 2013. Most lithium-ion battery fires and explosions come down to a problem of short circuiting. This happens when the plastic separator fails and lets the anode and cathode touch. And once those two get together, the battery starts to overheat.
Researchers have long known that high electric currents can lead to "thermal runaway" – a chain reaction that can cause a battery to overheat, catch fire, and explode. But without a reliable method to measure currents inside a resting battery, it has not been clear why some batteries go into thermal runaway, even when an EV is parked.
With their comparative low weight, low self-discharge and very high energy density it’s clear these batteries are here to stay, at least for now. But with such a high energy density comes a price, when these batteries fail, they can do so quite catastrophically, leading to fire and even explosions.