It looks like it has not been posted here...
In their
FAST magazine Airbus talks about "Taking lithium-ion technology to new heights" from page 32 on. Worth a read.
Looks like that battery is quite different from the one on the dreamliner.
In line with the discussions we had here some years ago, the did not only go to a different chemistry, but also to cylindical SAFT cells, which are much more robust than the rectangular YUASA cells, especially if you expose them to permanently changing air pressure.
Looks like the Airbus cast aluminum housing with venting does most of the tricks of the additional Boeing strong box already at battery level.
and
A350XWB Lithium Batteries A guide for fire fighters