In the past week, Samsung had to recall almost a million of its brand new Galaxy Note 7 smartphones. They had to recall because there were reports of the Note 7’s overheating and even in rare cases catching fires.

Fortunately there have been no cases of anyone being physically hurt, but there have been reports of property damage. Samsung is yet to explain as to why its smartphones are catching fire. Just like a lot of other smartphones, Samsung uses a rechargeable lithium ion battery.

In a report, Dr. Donald. R. Sadoway, the Jhon. F. Elliott Professor of Materials Chemistry at the Massachusetts Institute Of Technology has explained why are the lithium ion batteries are prone to catching fire.

First Dr. Sadoway offered a quick view at how the batteries actually work stating, “[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.”

He continued, “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.”

Then he offered his insight as to what might have happened with the Samsung devices by saying, “It’s either a statistical fluke in the manufacturing process where there are some local hotspots or there are perhaps some metal shavings, some kind of a shorting. But it seems as though, from what I’ve been able to read, the fires occurred when the owners are charging the phone. That means that while they’re forcing current through it, somehow there is a side reaction that is very different from just recharging the battery. And that starts charging the battery, and then the thing goes into thermal runaway.”