Our evidence for such a claim? A video that has surfaced of cells from a Leaf pack undergoing a battery of torture tests (pun somewhat-ashamedly intended). Shared by folks at the Hybrid Auto Center in Las Vegas – who offer for sale, among other things, used Leaf lithium battery modules – the footage shows salvaged cells being brutally assaulted with a screwdriver, and later, a propane torch. Granted, these tests are not the same thing as flinging a piece of metal into a working pack at 70 miles per hour, but they do claim to show that a puncture does not always equal a fire. Oh, and don't try this at home.
When pierced through by the flat head tool, there is no explosion or eruption of flame. Instead, a rather modest wisp of smoke shyly emerges as the electrolyte next to the shorted area of the fully-charged foil pouch reacts with the influx of oxygen. Again and again, the blade descends, until the cell is riddled with holes. No fire.
Amazingly, when connected with a voltmeter afterward there are still plenty of signs of life, and when it is charged and discharged (off-camera), it reportedly suffers only a slight loss of charge capacity. The video goes on to show another cell attacked with open flame with similar results.
While the demonstration is, perhaps, somewhat crude, the message it sends is loud and clear: lithium batteries can be safe and rather robust, despite some freak accidents. Scroll below to watch the short presentation for yourself.