What a puncture disrupts inside a phone battery
Most phone batteries store energy in thin layers: two electrodes separated by a porous, electrically insulating film. The film lets charged particles move during use while keeping the electrodes from touching. A puncture can tear through this carefully arranged stack, allowing the electrodes to make contact and creating an internal short circuit.
That short can release stored electrical energy as heat in a small area. The heat may damage more of the battery, making the short worse and causing the battery to heat even faster.
How heat can turn into fire
A lithium-ion battery also contains an electrolyte, the liquid or gel that helps charged particles travel between the electrodes. It can be flammable. If internal heating becomes intense enough, the electrolyte and other battery materials can break down and produce more heat and gas. This self-amplifying process is called thermal runaway: once it gets going, the battery can become difficult to cool, and hot gases or flames may escape through the casing.
A puncture does not guarantee a fire. The outcome depends on factors such as how badly the internal layers are damaged and how much heat builds up. But a battery can be hazardous even when the damage is hard to see from the outside.
Why the casing matters
The outer pouch or can helps contain the battery’s materials and keeps the layered components in their intended arrangement. It is not an impenetrable shield: a sharp object can breach it and damage parts inside that are much more delicate than the phone’s exterior.
That is why a damaged battery should not be pressed, bent, or handled as if it were merely a dented phone part. A tiny hole can cause a hidden electrical fault inside a tightly packed energy store.
