For as long as there is an internet to upload videos to, there will be idiots to stand in front of cameras and do stupid shit. This time it's more fools trying to see if smartphone batteries explode if you hit them with a hammer. Spoiler: they do, and it's crazy unsafe.
These two geniuses decided to get a battery out of what looks to be a Samsung smartphone and whack it with a hammer to test the hypothesis that it explodes when subjected to a good thwacking.
Just in case their theory proved correct, the whackee decided to take shelter behind a tiny piece of metal. Turns out that doesn't really work when the battery catches fire and flies above you from the resulting explosion.
In case you were wondering why batteries explode, it's because of a fancy scientific process known as thermal runaway.
It’s essentially an energetic positive feedback loop whereby increasing temperature causes the system to get hotter, which increases the temperature, which causes the system to get even hotter, and so on. Thermal runaway is surprisingly common and can be found in a wide array of physical and chemical processes, from curing concrete (which releases heat) to exploding stars (supernovae are the result of TR on a cosmic scale).
Li-ion batteries can suffer thermal runaway for a variety of reasons. Much like bridging a 9V battery’s terminals with a coin, short circuits caused by a tear in the membrane that separates the negative and positive poles of a Li-ion battery will often cause a thermal meltdown. Ambient temperatures exceeding 60 C, repeated overcharging, or unauthorised modifications to the case have all also been reported as the source of battery fires.