> lithium ion batteries don't even need oxygen to burn as they're self oxidizing
This is incorrect. I don't even know where this bullshit originated.
Flame testing is a routine thing - it's really good to know what kind of fumes and particles a fire might be producing, y'know? - and while the proportions of combustion products for lithium batteries varies with the exact chemistry and state of charge, they always produce non-trivial amounts of carbon monoxide, carbon particulates (soot), and hydrogen gas.
You do not get any of those combustion products if there is excess oxygen available, which you'd think there would be if you had both ambient air AND supposed oxygen generation within the chemical reaction itself. Instead, you always get incomplete combustion characteristic of a insufficient oxygen.
As with any fire, you can put them out by depriving them of air. What you can't do is prevent the other chemical reactions from continuing to generate heat by simply cutting off the oxygen, which is a separate issue. This is why a constant flow of water is recommended to extinguish battery fires; to keep them cool so the flammable chemicals stay inside the cells where there is no air to support combustion.
=Smidge=