Lithium being an alkali metal can react with water to form hydrogen gas (which is explosive in air) as follows:
2 Li + 2 H2O -> 2 Li+ + 2 OH- + H2
However, apart from Li being the least reactive among the alkali metals, there is no metallic Li in rechargeable Li-Ion batteries (as opposed to non-rechargeable Li cells).
Immersion in water works well for Li-Ion battery fires simply because water quickly absorbs excess heat, i.e. cools down the battery such that any thermal runaway reaction can no longer proceed.
Last edited by olandese_volante; 25th Sep 2016 at 01:44.
Reason: tweak