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Why Electric Cars Burn, Why It's Probably Overhyped and How to Fix It

EVs aren't the scourge that headlines suggest, but here's how to make sure they don't become one.

This story is part of Plugged In, CNET's hub for all things EV and the future of electrified mobility. From vehicle reviews to helpful hints and the latest industry news, we've got you covered.

Lithium ion batteries do two things really well: They power a wide range of devices, from tiny Samsung Z Flip phones to huge Tesla Semi trucks, and they burn well. Here's why they burn, how to keep that in perspective and what can be done about it. 

A perverse power source

Lithium ion batteries are rather perverse: They've invaded every corner of our homes, pockets and roads, but they're also perfect little fire-starting kits. The moist solution inside them is highly flammable at room temperature, the internal part of the battery called the cathode is a source of oxygen, and if the battery's internal parts contact each other improperly they quickly heat up enough to ignite the whole mess. It's no wonder the Federal Aviation Administration and major shipping companies have very stringent rules about carrying them.

Lithium battery shipping label

The shipping labels on products with lithium ion batteries are clear and stark.

Amazon

Ugly headlines

The big bang for lithium ion fire awareness was the star-crossed Samsung Galaxy Note 7 that was banned from commercial planes in 2016. Any Tesla fire is a headline event, largely because Tesla is always a headline event, but Chevy Bolts last year were subject to a warning from GM to park them outside and away from other cars while the company addressed a battery fire glitch. And now electric scooters and bikes are grabbing headlines as some multiunit buildings ban them and the New York City Council mulls new rules that would ban the use of second-hand lithium ion batteries that often find their way into indifferently designed products. 

The Consumer Product Safety Commission has documented 25,000 reports of lithium ion batteries seriously overheating between 2017 and 2021, not including cars and other vehicles, which are outside its purview.

What starts a battery fire?

Lithium ion batteries typically burn when one of four situations occur, according to research from the Occupational Safety and Health Administration:

  • Improper charging. 
  • Excess draw on the battery.
  • Swelling and rupture of the battery due to poor design, manufacturing or charging.
  • Physical damage that causes internal parts of the battery to contact in an unmanaged way.

Unfortunately, most of these issues are beyond the user's direct control; Only the prevention of physical damage is a factor we can actively prevent as end users.

Lithium ion battery AA burning

Your average alkaline AA battery won't do this, but lithium ion batteries are different (so don't try this).

CNET

Extinguishing burning cars

Professional firefighters I've spoken to say that handling a burning EV is actually rather low tech: They use enough (and often a lot of) water to contain the overall fire, let the battery burn itself out and keep the extinguished hulk of the car isolated for days in case remaining cells reignite, which is not unheard of.

There are oxygen-depriving fire extinguishing blankets that are used on car fires, but they have little unique effect on an EV fire since the battery is in the bowels of the car and is a self-sufficient source of oxygen.

Fire extinguishing blanket

Fire extinguishing blankets only go so far with EV fires since the battery releases its own oxygen supply and is deep in the belly of the car.

Zaragoza

Let's bring down the temperature

Cars burn all the time -- about 500 times a day in the US -- and rarely are they electric car fires. Besides being ubiquitous, gas-engined cars are fire-starting kits in their own right. If cars didn't exist yet and I described to you a vision of vehicles with 20 gallons of gasoline slung under them in an exposed thin-walled metal tank that supplies a high-pressure plumbing system snaking around an engine that's hundreds of degrees hot, you'd send me back to engineering school. But that's exactly what we drive.

Highway car fire

Cars burn all the time. We only notice it when they're electric.

Getty Images

Electric cars, on the other hand, have sophisticated thermal management systems that gasoline cars have no equivalent of in their fuel supply system. And EVs are in the early days of convulsive improvement of these systems, where gas-engined cars have turned over most of their safety stones. I'd bet on EVs being safer in the medium and long term. 

Lithium ion isn't one thing

"Lithium ion" is a catch-all name that includes combinations using nickel, manganese, cobalt, aluminum, iron and other minerals and metals. One of the more interesting is a lithium ion variant called lithium iron phosphate (LiFePo4). A recent FAA test found that this formulation produces the lowest temperature rise of lithium ion types during thermal runaway as well as having less propensity to ignite adjacent cells when one catches.  

FAA test results for lithium ion burning behavior

Lithium iron phosphate versions of the lithium iron battery family (blue bars) tend to be less hazardous, according to FAA flammability research.

FAA

Conveniently, lithium iron phosphate batteries are having something of a moment right now, with Ford among automakers that are embracing the formulation because it happens to also be good at handling many charge cycles with little capacity loss and uses a core material that is cheaper, plentiful and less toxic, both chemically and politically. The downsides to lithium iron phosphate batteries is that they tend to be a bit heavier and have lower energy density than some other formulations, requiring more battery to get the same range. But since most of us wildly overestimate the range we need in an electric car, that may be a moot point.

The other potential battery safety breakthrough might come from solid-state batteries, which do away with most or all of the flammable slurry inside today's lithium ion batteries. According to a recent study by the Sandia National Labs, solid-state batteries do seem to be much safer, though they will combust when pushed beyond reasonable limits.

Battery fire safety matters because as goes our perception of it so goes much of our perception of safely using and parking electric cars, scooters and bikes.