You want to stop a lot of these "exploding" smartphones?
Real simple...BEEF up the exterior of the phone, and get rid of the idea of a "slim stylish light" phone!
The manufacturers, want a battery life of a typical day, with a little left over. The phone industry, driven
by marketing, says everyone wants a THIN phone that is stylish, good looking bla bla bla.
Engineers then are tasked with trying to stuff as much battery, in a very finite space, with very little
breathing room left over. People, continue to carry these phones in their pockets (if you ever catch them
with it NOT in their hands 24/7). That constant strain of flexing the device, with a very thin case (apple bendgate ring a bell?), coupled with the limited space inside the phone, coupled with stuffing as much battery as possible in the phone, will cause these soft batteries to flex. If you've ever taken a piece of metal and bent it back and forth enough, you know what happens. Same thing in a battery. The separator, that keeps the cathode & anode, along with the electrolyte from all getting together at the same time, will eventually fail, with dire consequences!
Lithium batteries, be they the LiOn, or the polymer types, do NOT like to be disturbed. Take one out, lay it on concrete, whack it hard with a hammer and watch what happens. Makes for a wonderful fire starter.
The charging circuit is suppose to stop current flow, when the battery has reached a pre-programmed level. If that fails, the battery heats up. The second layer of protection, is a thermistor, which senses heat. When the heat reaches a programmed level, it breaks off current flow to the battery. If that fails, the third layer of protection, and the final layer, is a thermal fuse. Once the heat reaches that, the fuse literally melts in two, breaking the connection, requiring the battery to be replaced. These circuits usually are effective, but, with the limited space, high capacity batteries, and flexing of the cells inside, all bets are off.
Go back to making a bigger, thicker case that gives the battery a little wiggle room, and also stiffens up the case, and you'll see the bulk of these problems disappear.