Not really sure how this happened but the positive lead on this battery snapped clean off at the solder point. Is there anything special I need to know before trying to solder it back on? I’ve seen LiPo disaster flicks on youtube… I’d rather not DIACF if I can help it.
Commercially produced tabs are generally resistance welded for this reason. It’s not clear to me if you’re asking about the tab itself, or a wire attached to the tab. Soldering onto the tab is probably safe if you’re careful to not dump too much heat into the cell itself. It should be doable with the cell remaining cool enough to touch.
If you’re trying to reattach the welded tabs, I might avoid this myself, or at least wear gloves & glasses and do it outside. The battery case will have a fair amount of thermal mass and good thermal conductivity from where you’re trying to solder. I think it would be hard to get the case hot enough to wet without damaging the battery (I believe heat is not good for their capacity) or causing a dangerous scenario.
I’ve soldered straight onto Li-Ion batteries without issue. The biggest thing is don’t short them, or do anything that can cause a short internally.
Best way to attach leads to tabs or to the end face of batteries is through spot-welding 'em. We do have a spot welder at the space, at least we used to… You might need to make a new sort of clamp for using it on a battery though.
sorry, added a photo to OP this is the best i can get of the point where it broke. It LOOKS like the break is at a point where the wire was soldered to a PCB along the edge of the battery. Battery is from Adafruit, if that helps any at all…
Looks like it goes to a protection PCB, which you can solder to normally. Remove the kapton tape and replace with new stuff.
That was what I was thinking, but I’ve seen the worst… I prefer to double check… it’s what I pay you for, minion! 
Thanks