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> Why not just grind them up in a vacuum chamber? Because the energy stored in the chemistry of them doesn't care about oxygen and will happily come out in a h
by Syonyk 6y ago
> Why not just grind them up in a vacuum chamber?
Because the energy stored in the chemistry of them doesn't care about oxygen and will happily come out in a hurry. Look at some of the videos of a crushed 18650 - they don't get any oxygen in them, but they sure make a nice little firework.
The exothermic runaway is totally oxygen independent, and evolves a variety of nasty chemical cocktails out of the electrolyte. Those then tend to ignite when they find oxygen, creating a blowtorch (but less toxic gasses - pick your poison, literally).
If I recall properly some papers I read, about half the energy released in a battery runaway is the chemical/electrical energy, and the other half is the chemical breakdown and electrolyte decomposing/burning. So, if you have a 3.7V nominal 100Ah cell, that's 370Wh electrical, and about 740Wh total. Dump that in 15 seconds, and you have a nice ~175kW event to deal with. In any case, it happens quickly enough to be the sort of excitement you want to be upwind of.
But grinding batteries is more challenging than it sounds.
If they're mostly or fully drained, there shouldn't be enough energy left to get really exciting, but now you need the labor of manually draining each battery before recycling, or you soak them in a salt water bath for a while and deal with the corrosion (salt water is conductive enough to slowly drain a battery without it getting exciting, and it keeps things cool enough that if a cell tries to get exciting, it shouldn't be able to propagate).
"Replacing parts without having to go through the smelters" is what the goal is here, it just requires some things to be true about batteries that, to the best of my knowledge, aren't broadly true.
Again, I'd love to read the article, though, if anyone has access to it.
- londons_explore 6y agoPut a burning lithium phone battery in a vacuum chamber... The battery expands dramatically and the flames go out within about 10 seconds... Just try it.
- virtue3 6y agobut then you probably don't have much to recycle if it combusts eh?
- Syonyk 6y agoThe flames may go out from lack of oxygen, but that doesn't mean that the internal thermal runaway has halted. There are two processes going on in a flaming lithium battery - the internal exothermic runaway, which heats up the electrolyte and various other things enough to gas and escape, and then the combustion of those gasses in atmospheric oxygen. The vacuum chamber will terminate the flaming combustion part, as there isn't any oxygen left to burn the gasses with (leaving a rather more toxic cocktail of stuff including HF in many cases), but it won't do a thing for the internal runaway. To stop that, you've got two options: Cool the pack sufficiently to get everything below the exothermic point, or wait for it to run out of stuff to react. Also, I've no interest in "just trying" lithium pack runaways. I've rebuilt a number of lithium packs for people over the years, and I've tried very, very hard (and so far successfully) to avoid that sort of thing.
- londons_explore 6y agoThe evaporating electrolyte cools the whole thing down very quickly. It's icy cold when you get it out.
- Syonyk 6y agoThat's a possible mechanism, hadn't considered that. However, a brief survey of gasses coming out of a runaway still puts it on the list of "Things I have no interest in coming near."
- hinkley 6y agoDraining is something that you should be able to automate, especially if you are selecting for cells that are not damaged.