Disposable vapes are indefensible. Many, or maybe most, of them contain rechargeable lithium-ion batteries, but manufacturers prefer to sell new ones.
To make a point about how wasteful this practice is—and to also make a pretty rad project and video—Chris Doel took 130 disposable vape batteries (the bigger “3,500 puff” types with model 20400 cells) found littered at a music festival and converted them into a 48-volt, 1,500-watt e-bike battery, one that powered an e-bike with almost no pedaling more than 20 miles. You can see the whole build and watch Doel zoom along trails on his YouTube video.
I would design the pack with a thermal fuse of about 60 degrees C stuck between each 3 cells.
This way if one of those crappy cells start overheating the fuse should prevent it from going into thermal runaway.