Samsung held a grand Unpacked event in August to unveil its most promising device ever, convinced that this device would finally let the tech giant claim the throne it sought so badly. However, the turn of events since then has been a living nightmare for Samsung. What is even worse is that the root cause of these Samsung Galaxy Note 7 explosions is not yet known, even after all the engineers at Samsung tirelessly tried to find the flaw. However, folks at Instrumental did their own R&D alongside and have come up with a potential theory explaining these explosions.
According to a report by Instrumental, the aggressive design strategy of cramming the biggest possible battery into the smallest possible frame is what caused the Galaxy Note 7 to explode. The large battery inside a 5.7-inch device with all the other features, including a separate slot for the S Pen to fit in, has reportedly been the cause of these explosions. To fit the large battery, Samsung left virtually no space (less than 0.1mm in some places) around the circumference, when the company ideally should have left a 10 percent gap for the battery to expand over time. The compression of the battery thanks to the stress of being placed in pockets, alongside the natural swelling, is reportedly the driving factor causing many Samsung Galaxy Note 7 units to catch fire.
The Note 7's lithium-polymer battery is a flattened "jelly-roll" consisting of a positive layer made of lithium cobalt oxide, a negative layer made of graphite, and two electrolyte-soaked separator layers made of polymer. The separator layers allow ions (and energy) to flow between the positive and negative layers, without allowing those layers to touch. If the positive and negative layers ever do touch, the energy flowing goes directly into the electrolyte, heating it, which causes more energy to flow and more heat - it typically results in an explosion. Compressing the battery puts pressure on those critical polymer separator layers that keep the battery safe.
Samsung stated that these separator layers may have been thin to start with due to aggressive manufacturing parameters. Add some pressure due to normal mechanical swell from the battery or accumulated stress through the back cover (e.g. from being sat on in a back pocket), and that pressure could be enough to squeeze the thin polymer separator to a point where the positive and negative layers can touch, causing the battery to explode.
If this is true, this design ignorance proved to be fatal for the company - both in respect of brand value and monetary losses. The report also stresses that the recall was imminent, as the problem would've worsened in the future. For those Galaxy Note 7's that didn't explode till recall, would do so eventually, as the battery tends to swell up through continual recharging over time, and with no place to expand, the smartphone would explode under pressure.