glad_rag:
Enclosing [robustly] something that may explode....won't that just make it worse?
In the case of a sealed container, you would be correct. However, the current 787 container can vent (and did so in the case of JA804A) and the new container would include active venting to the outside of the plane. This is something Airbus has for the Li-Ion batteries on the A350XWB (and yes, I know Airbus will be moving to NiCad for certification and on production frames, but MSN003 and her sisters will start their flight tests with Li-Ion).
Interestingly, the 777 NiCad battery is in a sealed container. I guess they never expect anything to go wrong with it.