(LiPF6) or other Li-salts containing fluorine…
A lithium fire is difficult to extinguish,
mainly because of the way lithium reacts
with water. Immediately upon contact with water,
lithium produces hydrogen gas & lithium-hydroxide.
Lithium-ion batteries use a flammable electrolyte
that contains lithium hexafluorophosphate,
which can decompose into the thoroughly
unpleasant hydrofluoric acid during a fire.