I used to be a rep for a lipo brand, commonly used in electric RC helicopters and drones. Those battery cells are wrapped in a membrane that's very easy to puncture if poked or slid into another object. Think heavy duty potato chip bag material. I've seen many go up in flames when a helicopter crashes or some component shifts and vibrates a hole in a battery cell. Almost always when a cell erupts, each neighboring cell will sequentially erupt as well. Most of the 5 and 6 cell lipos would hiss smoke and spew sparks and flames for at least a minute or so before burning out.
I understand the lithium ion round cells are physically protected better and less subject to unintentional damage but I never worked with them.
I would feel comfortable flying with scattered lipos in devices on airplanes, or even in cargo, but a container with dozens or hundreds of the fragile cells in one container does make me uneasy. I carry them in my car trunk and am constantly checking that no tools, volt meter probes, or any hard object can slide or shift into a cell. We really are at the mercy of the person doing the packaging. One slip up and a large number of cells could be affected.
Interestingly the bluefin sonar thing that searched for mh370 is powered with lipos. From what I read the high pressure from extreme depth is not a problem for lipo cells.