Do Lithium-Ion Batteries Have a Fire Problem?

Google “Tesla battery fire” and you’ll find no shortage of results. Just last month, USA Today reported that California firefighters had to use 4,500 gallons of water to douse one of the brand’s EVs. And Tesla certainly isn’t alone: recalls and fire safety problems have plagued brands like Lucid, Rivian, and Chevy. But what causes these incidents? And how do you weigh the risk against a traditional internal combustion engine?

Lithium-ion batteries, like the ones used in almost every EV on the roads today, are designed to store as much energy as possible in the smallest space possible. This creates a lot of heat when energy demand is high. This principle is obvious to anyone who has ever noticed their phone or laptop battery getting hot with extended use. And because lithium-ion batteries can only safely operate with a narrow range of temperatures, most modern electronics—and EVs certainly—have numerous safeguards in place to prevent batteries from getting too hot. Almost all modern smartphones, for instance, will simply shut down if they get too hot. Nearly every EV on the road has complex cooling systems to manage the thermal strain on their batteries and multiple failsafes. When everything is working as intended, the battery should never get dangerously hot.

But crashes and malfunctions do happen. If a piece of road debris or a crash damages a battery, fire is certainly possible. A design flaw or manufacturing defect can also create a dangerous situation. The thing that makes lithium-ion battery fires so serious is that they create a feedback loop known as thermal runaway: Once the battery overheats the electrolytes in the cell catch on fire, which creates more heat, which ignites more electrolytes, etc., etc.

Traditional means of stopping the fire, like dousing it in water, are often insufficient to put out the flames because the battery packs are hard to reach and retain enough heat to reignite over and over again as soon as the water stops flowing. In 2019,Firefighters in the Netherlands were forced to submerge a BMW i8 in a tank of water for 24 hours due to a particularly persistent battery fire.

While lithium-ion battery fires are nasty and dangerous, calculating the risk they pose to drivers presents a somewhat different picture. A 2017 report [PDF] from the National Highway Traffic Safety Administration, concluded that

“…the propensity and severity of fires and explosions from the accidental ignition of flammable electrolytic solvents used in Li-ion battery systems are anticipated to be somewhat comparable to or perhaps slightly less than those for gasoline or diesel vehicular fuels. The overall consequences for Li-ion batteries are expected to be less because of the much smaller amounts of flammable solvent released and burning in a catastrophic failure situation.”

TL;DR gasoline is also flammable and internal combustion engines still have batteries.

So, while it may be tempting to think that EVs pose an increased safety risk due to their lithium-ion batteries, the best data we have right now suggests that they’re no more dangerous than gas cars. Furthermore, numerous new battery technologies could reduce the risk of fire substantially.

Solid state batteries, for example, are often touted as being ore stable and less likely to ignite, though some research suggests the question may be a bit more complex than that. Other companies, like Battery Streak, in Camarillo, CA, are adding exotic materials to more traditional lithium-ion battery formulations in an effort to improve the thermal characteristics and performance.

If any of these companies can find a way to reliably mass produce these batteries and get them into EVs, the cars of tomorrow may prove considerably safer than anything on the road today, at least in terms of fire risk.