REVEALED! Battery Expert explains Why Samsung’s Phones Are Catching Fire

Samsung announced last week that it’s recalling millions of its new Galaxy Note 7 smartphones amid reports the devices were overheating and, in some cases, catching fire.
There haven’t been any known cases of people being physically hurt by the phones. But the devices are being blamed for fires that destroyed a Jeep and did serious damage to a garage. Meanwhile, U.S. aviation officials are now telling fliers to avoid turning the phones on in flight.
The South Korean electronics manufacturer has yet to explain exactly what’s causing the fires. What we do know, however, is that the problem stems from their battery.
Like almost all modern smartphones and lots of other consumer electronics, the Note 7 uses a rechargeable lithium-ion battery. Electronics companies favor these kinds of batteries because they’re cheap, they pack plenty of power, and they don’t lose a lot of their charge over time when they’re sitting idle. Yet they have also been involved in several high-profile fire incidents, including episodes that more or less ended the hoverboard craze and caused problems with Boeing’s 787 jetliner.
How do lithium-ion batteries work, and why do they seem to be prone to catching fire? We asked Dr. Donald R. Sadoway, the John F. Elliott Professor of Materials Chemistry at the Massachusetts Institute of Technology (and onetime TIME Most Influential Person), to explain. First, he offered a quick primer on battery chemistry:

[Lithium-ion batteries] are a classical battery in the sense that they have two electrodes separated by an electrolyte. In this case, the negative electrode is typically some kind of a carbon, like a graphite, and the positive electrode is a metal oxide, something like lithium cobalt oxide or lithium manganese oxide. The electrolyte, because it’s shuttling lithium, it has to be non-aqueous. They can’t use an acid or an alkaline solution, they have to use something that’s not water, and that’s part of the problem. It’s an organic liquid and so therefore it’s volatile and flammable. But it does dissolve lithium salt and it allows lithium to shuttle back and forth between the negative electrode and the positive electrode.
Let’s [talk about] the battery at full state of charge. At full state of charge, all of the lithium is up inside the negative electrode. It’s sitting inside the graphite. On discharge, the lithium wants to go from the graphite over to the cobalt oxide. So it takes a swim through the electrolyte and enters the cobalt oxide, and electrons go through the external circuit and power your devices. That’s what generates the current and so on.