You plug your Samsung Note 7 smartphone into the bedside charger and place it on your nightstand with care.
You wake to find your nightstand in flames, smoke billowing everywhere.
Or maybe your Jeep. Your hotel room. Your entire home.
How could this have happened? Simple: your phone is a Samsung Galaxy Note 7 — and it’s one of over a hundred that have spontaneously burst into flames.
After 35 reported incidents of overheating smartphones worldwide, Samsung made the unprecedented decision to recall every single one of the Galaxy Note 7 smartphones sold. That’s said to be 1 million of the 2.5 million that were manufactured. (Since the recall was first announced, the number of explosive Note 7s has nearly quadrupled.)
Samsung has reportedly suspended production of the company’s Galaxy Note 7 smartphone because the devices — plagued by battery problems that were causing some phones to catch fire — are still at risk of exploding.
“Battery failures are exceedingly rare,” says Donal Finegan, a chemical engineer at University College London. “Any kind of fault does garner a lot of media attention and can really affect the reputation of a product that relies on the battery.”
Like many rechargeable devices, phones use lithium-ion cells. But what makes these batteries great at powering gadgets also makes them vulnerable to catching fire, says Finegan. “They are so energy-dense and can operate under such high power that they can combust in a particularly catastrophic way.”
How does a lithium ion battery work?
Like any other battery, there are three parts to a lithium ion battery: the anode, cathode and electrolyte.
The anode and the cathode are electrical terminals called electrodes, and the electrolyte is the chemical in between them that conducts the electricity.
While the cathode holds positively charged ions, the anode holds the negatively charged ones. Both anode and cathode are in the electrolyte but are separated by a physical barrier so they can’t touch.
When the phone is being used, charge is pushed from the positive cathode through the electrolyte and attracted to the anode before flowing out to the different components of the phone. Once you’re plugged in and charging, this process is reversed.
Why do they blow up?
Lithium ion batteries begin to degrade almost immediately after leaving the factory. This is why a two-year old phone won’t keep charge as well as a six-month old one. What’s more, they’re very sensitive to high temperatures.
Secondly, when the (extremely volatile) electrolyte is inside a sealed battery case (like in a smartphone) pressure builds up and, on rare occasions, will actually puncture the casing.
That’s when the electrolyte (which is more like a paste than a fluid) seeps out and comes into contact with the other components of the phone.
In these cases, it can ignite and set other parts of the handset on fire.
Just because a simple phone could turn into a destructive inferno doesn’t mean that it will — even if it’s a new Galaxy Note.
According to an unnamed Samsung official who spoke to Yonhap News, the Note 7’s manufacturing defect affects less than 0.01 percent of all Note 7 handsets sold. Some quick back-of-the-envelope math, and you’re potentially looking at fewer than 1,000 defective phones. “It is a very rare manufacturing process error,” a Samsung rep told CNET.
But it’s the damage those phones can cause, and the frequency with which they’re causing damage, that makes the Note 7 dangerous.
While CNET tends to hear about just a few exploding devices each year, Samsung’s Galaxy Note 7 has caught fire as many as 112 times after only one month on sale.
(That’s based on official tallies of 92 incidents in the US, plus at least 17 in Korea, 1 in Taiwan and 2 in Australia.)
Why Note 7?
What makes the Note 7 different: Samsung may have accidentally squeezed its batteries harder than it should.
According to a unpublished preliminary report sent to Korea’s Agency for Technology and Standards (obtained by Bloomberg), Samsung had a manufacturing error that “placed pressure on plates contained within battery cells,” which “brought negative and positive poles into contact.”
“The defect was revealed when several contributing factors happened simultaneously, which included sub-optimized assembly process that created variations of tension and exposed electrodes due to insufficient insulation tape,” a Samsung representative tells CNET.
Or, in plain English: the thin plastic layer that separates the positive and negative sides of the battery got punctured, became the shortest route for electricity to zap across the battery (that’s why they call it a “short-circuit”), and became a huge fire risk.
What does pressure have to do with it? MIT materials chemistry Professor Don Sadoway explains that today’s cell phone batteries are made by literally pressing together a stack of battery components — and that battery companies are under pressure (no pun intended) to cram in as much battery capacity as possible.
“Imagine if you had a toilet paper roll and it wasn’t packed tightly,” says Sadoway. With the same size roll, you’d run out a lot quicker.
At first, Sadoway has two theories: perhaps Samsung simply pressed so hard that the positive and negative terminals poked right through the separator and managed to touch.
Or perhaps it’s the sponge-like separator itself that got squished. Normally, says Sadoway, the separator allows the liquid electrolyte to pass through pores connecting the negative and positive sides of the battery, even as it keeps the two terminals separate. “If they press really hard, they constrict the pores, the resistance goes up and you generate more heat,” says the professor.
But there’s another, more interesting theory: perhaps Samsung’s batteries are skewering themselves on their own tiny spears.