the cause for the explosion is by rechargeable lithium batteries are more susceptible to overheating than other types of batteries if they are exposed to high temperatures, are damaged or have manufacturing flaws. Once the overheating starts, it can lead to "thermal runaway"
The science behind phone battery fires is phones use lithium ion battery packs for their power, and it just so happens that the liquid swimming around inside most lithium ion batteries is highly flammable.
If the battery short-circuits It heats up the (flammable!) liquid electrolyte at that spot. And if the liquid heats up quickly enough, the battery can explode.
http://cnet.co/2fUujIY
The incident made U.S. aviation safety officials took the extraordinary step warning airline passengers not to turn on or charge a new-model Samsung smartphone during flights following numerous reports of the devices catching fire.
The Federal Aviation Administration also warned passengers not to put the Galaxy Note 7 phones in their checked bags, citing "recent incidents and concerns raised by Samsung" about the devices. It is extremely unusual for the FAA to warn passengers about a specific product.