Right.lithium batteries do NOT contain lithium metals...its a lithium salt so there is no worry about active lithium.
the problem with lifepo4 is that it is a high energy object and using something like inert gases or water to "oxygen starve" the energy release does absolutely no good at all...
most fire suppression is to stop "burning" which is the oxidation of the material...burning wood/plastic/whatever...you get rid of the oxygen and the fire stops.
batteries would "burn" in a vacuum because they are dumping stored energy!
you are not going to put it out, your goal is to isolate and minimize damage to surrounding areas.
But the cells themselves are not where the fires start. Will has a bit of an open bounty on evidence of lifepo4 cells actually catching fire themselves, rather than surrounding wiring or components. Overcharging or overdischarging or physically puncturing the cell just offgasses without catching on fire.
The other things around the cells is what you need to stop before the cells are destroyed and start contributing their electrolyte to the burn.