Fireproof batteries have, in the past, never really measured up, but the most recent attempt at birthing the safety-minded technology seems to have hit a breakthrough that could allow fireproof batteries to exhibit performance similar to, if not the same as, their non-fireproof brethren. Researchers at Stanford University are calling it an "electrospun core-shell microfiber separator with thermal-triggered flame-retardant properties". In short, these batteries contain a thermally reactive component that melts away when things are getting too hot, and deploys a flame-retardant microfiber to separate the layers of the battery and, hopefully, stop a device fire before it has a chance to start. The technology is currently in the earliest of stages, and does not yet have a tentative release date of any sort for use in consumer products.
The way that a battery catches on fire, in most cases, is pretty simple. Something creates a connection between the two halves of the battery and the highly flammable electrolytes in the anode and cathode sides of the battery react with one another and create excessive amounts of heat. Packed into a small battery, the head is cycled back into the electrolytes in a vicious cycle called a thermal runaway. Eventually, the heat gets to be too much for the surrounding materials, and they go up in flames. One way to prevent this is to put a flame-retardant material or compound into the battery, but this normally ends up degrading performance somewhat.
The research at hand has resulted in a specialized polymer shell made with a low melting point. If a battery gets hot enough to merit a possible thermal runaway, the polymer shell melts, and a flame-retardant microfiber unfurls from within it, cooling things down in short order. The flame-retardant agent on the microfiber leaks into the anode and cathode electrolytes, neutering their heating abilities. Should runaway continue despite this, the microfiber itself is heavily treated for flame resistance, and will stop a swollen, smoking battery from physically lighting up. While this approach is not as ideal as stopping a thermal runaway before it starts and preventing the battery from getting hot, or even stopping the root cause of a runaway and saving the battery, it will certainly suffice to prevent a large number of the exploding phone stories that pepper the mobile news scene each year.