Let me say at the outset, DO NOT TRY THIS AT HOME! Just about all of us carry cell phones that contain lithium-ion batteries (also known as Li-ion batteries), and we would never even remotely think of our phones as being flammable.
The person who made this video was obviously fascinated with seeing what would happen if he poked his cell phone with a sharp knife, into the battery itself. Although it is highly unlikely that our phones would ever spontaneously combust, watching what happens in this video took my breath away.
Although, with the current batteries we certainly have no reason to be concerned about flammability under normal circumstances, it might be a good thing to have a safer option to these Li-ion batteries. Something was discovered recently, by researchers who were attempting find a material to use on the bottom of ships, that would prevent marine life from attaching to the bottoms. In their research they made an incidental finding of a way to make non-flammable Li-ion batteries. PFPE is a material that has a similar chemical structure of the electrolyte used in the current batteries. It is being tested with the hope that they will be a marketable alternative, so that the batteries in cell phones will no longer have combustable potential. When you watch how quickly the phone blows up when prodded in this video, you may agree that it would be good to find a non-flammable alternative. It was definitely a bit scary how rapidly the phone went up in flames.