Days after a fiery crash, a tesla’s battery keeps reigniting – slashdot electricity questions and answers pdf


Six days after a fiery crash on Highway 101 involving a Tesla Model X took the life of a 38-year-old San Mateo man, the car’s high-voltage lithium-ion battery re-ignited while sitting in a tow yard, according to the Mountain View Fire Department… The battery reignited twice in the storage yard within a day of the accident and again six days later on March 29. Two weeks later, in an effort to avoid more fires, the NTSB and Tesla performed a battery draw down to fully de-energize it…

On the company website, Tesla wrote "the reason this crash was so severe is that the crash attenuator, a highway safety barrier which is designed to reduce the impact into a concrete lane divider, had either been removed or crushed in a prior accident without being replaced. We have never seen this level of damage to a Model X in any other crash"… Tesla also reported that the vehicle’s autopilot function was active at the time of the crash…

The National Transportation Safety Board is investigating the Highway 101 crash and three other accidents also involving Teslas, including a fiery 2014 Model S crash Tuesday in Florida that killed two teenagers. Also under investigation: A Model S crashed into a fire truck near Culver City in January, and the driver reportedly said Autopilot was engaged at the time. And it is looking into a battery fire of a Model X that drove into a home’s garage in Lake Forest in August.

Electrical energy stored != combustion potential energy, and combustion potential energy != energy that can be practically released in normal circumstances (there’s five times more potential energy to be released from the combustion of 1000kg of alumium or graphite vs. 1000kg of nitroglycerine, but which one would you rather be next to in a crash?).

It is not the "energy" stored in the batteries in "lithium battery fires" as you put it. First off, they’re lithium-ion batteries, not lithium batteries, and yes, there’s a big difference. There’s no metallic lithium in lithium-ion batteries unless they’ve been abused (plating out of lithium at the anode is a failure mode, due to attempting to overcharge a cell or charging at too low of temperatures – both of which are prevented in a proper EV battery pack). The power (not energy) of the cell may provide a (significant) short-circuit ignition source if crushed, but what happens thereout depends on the chemistry of the cell; the fire from a burning cell (in varieties that are capable of burning) is most often the electrolyte (of which there are many varieties). The rest of the cell just isn’t that flammable; the anodes are predominantly carbon (graphite or amorphous, sometimes with silicon) and the cathodes are metal oxides. The lithium itself is present as ions (hence the name) intercalated (in small quantities) in the lattices of the graphite and metal oxides.

What happens in a battery pack, however, is a bit different from an isolated cell. In a ruptured, internally-short-circuiting cell in a battery pack, the heat and contents are released, but they’re released into non-flammable temperature-regulated pack coolant. Aka, quenched. Packs also employ a variety of processes to physically isolate cells from each other. Normally, cell failures are self-extinguishing in a pack. The problem with this accident is that it was so energetic that it utterly mangled the battery pack. Which is hard to do, as the pack lies within the wheelbase, but "high speeds into a concrete barrier" is a huge amount of impact force. When storing this pack, there was almost certainly no coolant left, and a lot of damaged cells. Yes, the remaining charge was an ignition source, but it’s not what you see physically burning; on its own, a short circuiting cell just makes itself very hot. Anything that happens after that is a result of the consequences of that heat – and more specifically, the results of that heat on the electrolyte.

The battery catching fire is an interesting point. I’d be interested to know if the emergency responders initially followed the published guidelines for cooling the battery or if they stopped when they stopped seeing flames. Regardless, it’s an interesting point and an important one for the future.

Regarding the rest of the OP’s posting…yeah, 2 teens died in a Tesla in Florida while speeding 50-60 around a corner marked for 30 mph. Yes, a lady crashed her car into a Starbucks. Where are the headlines about some random kid who died in a pickup truck this weekend? I’ll bet you $50 it happened. Or the old lady in her Ford Fiesta who ran into a parked car? I’ll put $20 on that one. What, no national headlines on those ones? What gives? Or do we think miraculously owning a Tesla makes you immune to being a stupid/careless/human driver? I didn’t know Musk was advertising that feature. Is Ford? Honda? Lexus?

This story is news and headline worthy, because it shows that an EV battery in a crashed vehicle is more dangerous and volatile that people realize, and it requires special equipment and expertise to deal with. Right now I’m wondering about the life-cycle of these batteries

To expand…danheskett…the person bitching about the NTSB "solving private sector problems" on the taxpayer dime. You realize what you’re complaining about is, literally, the government doing the job we pay them to do right? Are YOU going to hold a car manufacturer accountable for putting a dangerous product on the road? Were you personally going to pony up the cash to fly out to the crash site, check the forensics, go over the debris field, and make sure that what happened was a genuine accident and not the result of some guy cutting corners in the factory to improve his bottom line by 1%?

No? You weren’t offering to do that? Gosh, I guess it’s a good thing we all pay taxes and the NTSB does this stuff so that the rest of us have at least some slight reasonable reason to believe that manufacturers are making quality products. Yes, even Tesla…but also GM, Ford, Acura, Porsche, Kia, et al. They aren’t doing those company’s jobs for them. They are, quite literally, capable of shutting those companies down if they find a critical flaw in their product. That’s not doing their job for them, that’s keeping your disingenuous, passive aggressive, Neanderthal butt safe.