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Comment by KennyBlanken | Hacker News Reader

Adding to this, a reminder that lithium ion batteries contain very little lithium, and it's not elemental - an extremely common misconception leading to people thinking that they can't use water to stop a pack undergoing thermal runaway / on fire - something that can only be stopped via the cooling effect of water.

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Training materials for firefighters use the phrase "copious quantities of water".[1] That's just for scooter and e-bike sized fires. FDNY recommends knocking down the fire with water to a level where a shovel can be used to dump the battery into a bathtub or bucket filled with water. That prevents re-ignition. FDNY has a huge problem with cheap scooters and e-bikes catching fire in residential structures.

Current thinking for electric vehicle fires is to let them burn out unless there's a threat to something nearby. If there is, 8 hours of spraying water on the vehicle usually works. But then the mess may re-ignite.

[1] https://drive.google.com/file/d/1Qxo7u9Z5cI1tNC5BzFwt9QOik78...

> FDNY has a huge problem with cheap scooters and e-bikes catching fire in residential structures.

For those interested, it's shitty imported cheap products, and/or (and I believe this is more common) cheap shitty third party chargers that overload the BMS/don't shut off correctly when they are supposed to.

Buy reputable brands (lots and lots of the scooters and e-bikes you see are just re-branded stuff from the same Chinese OEM) and don't get a third party charger, stick to first-party ones.

Easier said than done. Shopping on Amazon makes the cheap products look just as legitimate as the expensive products.

The one can look suspiciously close to the other, to the point that when I look at the individual cells I still have a hard time. Usually weighing them will give you some way to discriminate the cells, BMS's are totally opaque. If I have a hard time telling the knock offs from the real deal how do you expect someone that is only interested in the use, and not in the tech, to tell the difference?

Have you ever played around with putting water on a burning lipo pack?

I’ve damaged a number of lipo cell pouches (my hobby uses a lot of them) and water does make them burn more aggressively in the short term. It’ll go from smoldering to shooting a foot of fire with a splash of water.

So aside from the lithium, what is causing the runaway thermal to fire/explosion??

The electrolyte is very flammable and a short circuit provides the temperature to ignite it. Some lithium battery chemistries (LFP is probably the most common, but LTO as well) are much less likely to burn when they fail catastrophically.

Can LFP experience thermal runaway? I was under the impression you could put a nail through an LFP cell and It'd mostly be fine.

Yes, but it is the most tame of common chemistries.

https://pubs.rsc.org/en/content/articlehtml/2014/ra/c3ra4574...

Nickel and Cobalt. This metal oxids creates molecular oxigen.

This oxygen feeds the fire and make it hard to fight.

Lithium iron phosphate do not show this kind of reaction.

Yes and no. Lithium metal is the highly reactive element in batteries.

Similar to Hydrogen and Sodium, elements in the first column of the periodic table are highly reactive (flammable) because they readily give away their single electron in the outermost orbital.

Some Lithium battery variants might have marginally safer properties, but they are fundamentally volatile at full charge.

Commercial lithium ion batteries do not contain metallic lithium in the charged or uncharged state. They have lithium ions intercalated into the anode material in the charged state.

Primary (disposable) lithium batteries do contain metallic lithium in the charged state, and there are efforts to develop rechargeable batteries using pure lithium metal at the anode. Rechargeable batteries that contain metallic lithium anodes would be able to store more energy, but they are also more hazardous and currently have low cycle life.

Most batteries have lithium complexes (cobalt oxide, iron phosphate, and so on) though, not elemental Li, and so have different properties.

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