[bityard]

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.