First post in this group. Generally any lithium battery is rather dangerous. My experience stems from drone flight (lipos mostly), reasonable travel (airplane) and research to keep things safe.
Regarding "explode", that is a little hyperbolic. There is not really a "boom", more like a fizz that turns into a fire and possibly a jet of flame. Explosions are indeed possible under extreme circumstances (toss on on the BBQ maybe). But I would consider explosions less likely or of no creditable threat when handled correctly, in good condition, and kept in known temperature, load, and barometric pressure (including the air pressure and not enduring rapid pressure changes).
Regarding "self ignite": Totally possible, but with caveat. Damaged batteries, shorts, and other mechanical type failures may persist for a long time and then suddenly reach a point of failure. Take that definition as you wish, it straddles the yes and no.
Generally my experience with lithium batteries is electronic devices and drone batteries. The batteries are usually foil-like pouches where the material is contained. Most laptops and phones are of this ilk. Drone batteries and similar removable lithium batteries are commonly multiple pouches wired to get desired voltage where the size (mass) determines the amps available (mAh rating).
Lithium generally gets very mad when exposed to water or oxygen. Ruptures will begin a chain reaction that can be difficult to stop (let it burn out). Under stress (rapid charge and discharge) events are accelerated. Commonly before a battery fails it "puffs" and swells. Should the conditions contributing to this stress not be eliminated or decreased the battery will cook and "blow", to use a generic term.
From my reading the way to treat a lipo fire is salt water, bucket of sand, or bury the unit. The salt water has a chemistry angle I am not able to comment on, but look up "lipo safety" in any reputable Remote Control hobby area and you will get the basics.
When transporting lipos several best practices do apply:
- Do not transport via air such as belly of a plane, fed-ex air. The exceptions is when they are on your person. Keep the batteries (this is law) as carry-on where the temperature and pressure is controlled (for the humans). My batteries are always in a special double pouch and monitored by me the entire flight for any fluctuation of temperature.
- Place batteries as "storage" charged, nominally a 60% charge. Should the battery be too hot (charged up too much) or too low (under minimum safe voltage) the stability is decreased.
- Carry the batteries in a manner that they will not be ruptured. For example, I tape ALL the connectors to the side of the battery so the rectangle connector will be less likely to receive great pressure pierce the unit(s). In other words, meticulous packing.
- Use a LiPo safe bag (fiberglass lined fireproof bag). Team Blacksheep has a nice one with some good added info. http://team-blacksheep.com/products/prod:liposafety
- Keep your WH (watt-hour) in the legal limit. I think in the US you need to be under 10000 mah (not official number).
I point out much of this as the explode and self ignite fears are indeed valid, but in my professional(?) opinion they are all explained by poor handling, poor quality, and ignorance in general to the tech.
I have about 15 national flights so far w/full drone gear (10+ batteries) and I can tell you to expect security to think they are bombs (swipe test). Be nice, be cool, and be an ambassador to the hobby or activity you are engaging and explain why you have the units.
Also try to keep batteries in good working condition and in a positive appearance. I re-shrink wrap batteries if the original case starts to look like hell. In the post 9/11 era of flight, your rights are diminished and relatively low paid worker bees are your interface on the operational front line. Keep this in mind, things can escalate quickly and cause great distress or worse.
Good luck, hope I helped!