This video shows the propagation of thermal runaway within an LG 18650-S3 cell. X-ray imaging at 2000 fps was carried out at The European Synchrotron (ESRF).

More details about this experiment and more can be found at:

http://onlinelibrary.wiley.com/doi/10...

and

http://pubs.rsc.org/en/content/articl...