CT scans of 1k lithium-ion batteries show quality risks in inexpensive cells

sorry for a dumb question but are old dead cells still dangerous just sitting around?

I discovered an ancient powerbank the size of a deck of cards that I had not charged in many years, was blown up like a football (imagine an a sealed envelope but full of air)

So that's a dead cell which shouldn't have a charge left but I guess the chemistry is releasing gas?

Scared me, wrapped it in aluminum foil and put it outside asap

If the cell is fully discharged, there isn't much danger because all of the energy that _would_ cause an explosion/fire is gone.

However, a LiPo cell that has entered Spicy Pillow mode (empty or not) can still theoretically burst, leaking or spraying toxic materials everywhere. So you were right to put it outside. Make sure you recycle it appropriately, so that it doesn't go into a landfill and poison the drinking water of our grandchildren someday.