What would be the consequences of non-containment? Do those batteries swell and completely fall apart or do they just move a bit (if so, flexible cables and lea

What would be the consequences of non-containment? Do those batteries swell and completely fall apart or do they just move a bit (if so, flexible cables and leaving decent room for expansion should be enough)? Do they merely need the compression to achieve the rated energy densities, or do they fail dangerously because of insufficient compression?