harrisonpatm said:
Hm, who has more knowledge on this to explain why this happened? It's not like I'm abusing cells, far from it, but it picked LiFePO4 because I watched a dozen youtube videos of people shoving nails through them with no effect, some swelling and a bit of smoke at the most. What would cause the aforementioned cell to turn into a firework when they're "not supposed to"?
Probably the answer is that they're lower risk, but not zero risk. Still, annoyed that I did my research and picked these cells for my build so that I don't have to worry about fire, and now I'm worried!!!! lol
The above highlighted part is the answer.
Anything that stores enough energy can fail (or be caused to fail) in a way that can release that energy hazardously.
Even a spinning top (gyroscope) can be fatally dangerous, if it is either massive enough or spinning fast enough, and a mechanical failure occurs or is induced that fragments it or causes an extreme sudden drop in RPM (which could do that too, or heat it enough to fail).
Even a plain old lead-acid battery can explode, usually from hydrogen gas buildup inside the casing too rapidly for any vent to release. I've seen a car hood blown off and up quite a ways into the air by this (when someone was trying to jumpstart someone else's car--I don't know which one blew up).
NiMH and NiCd can also do this (almost 3 decades ago I blew up four AAAs by accidentally connecting them backwards, obliterating the plastic casing I'd built them into, and leaving cell shrapnel embedded in various places in the room).
There've been plenty of LiFePO4 failures / fires, some from damage, some from abuse, some from unknown causes; it's saf
ER than the typical cobalt-based lithium cells, but there's no perfectly safe kind of cell that still has energy in it.
As long as the pack is built well of known-good good-quality well-matched cells, with reasonable precautions against damage (mechanical or electrical or environmental), and is used reasonably, not abused, not damaged, not used outside it's limitations, it's unlikely to have a problem.
Stuff can still happen...and you can only do what you can do, so things can still go bad. It's just much less likely given the above, and more likely the less that is done to prevent or mitigate it.