How does a laptop battery ignite?

We came across a very interesting video on YouTube.

In the video, we can watch the destruction of a deliberately overloaded laptop battery for nearly five minutes, which initially emits only very strong smoke and then catches fire, and then the fire spreads nicely over the entire area of ​​the computer.

The topic is very topical, just think of recalling millions of flammable Sony units. Something like this could have been experienced by notebook owners who were in a hurry.