Here’s why Samsung Note 7 phones are catching fire – CNET

The Galaxy Note 7 is the “hoverboard” of 2016

A sneak peek at renders of the ne w Google Pixel phone. Plus, Samsung’s exploding phones and recall efforts go from bad, to really bad.

by Brian Tong

You plug your 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.) The company says it’s stopped all sales and shipments of the Note 7 and is working with government agencies and cellular carriers around the world to provide refunds and exchanges for the phone.

In every country, the message is the same: return your Samsung Galaxy Note 7 now, just in case something bad might happen to you. (Read our full recall FAQ.)


Don’t leave a Galaxy Note 7 on the charger. Return it for a refund now.

Josh Miller/CNET

The Note 7 battery fiasco is a huge black eye for Samsung, made worse by the fact that it’s playing out just as the company’s archrival, Apple, is releasing its new iPhone 7 and iPhone 7 Plus.

But how bad is it, really? What causes a phone to explode this way, and why this specific Samsung phone?

Here’s what we know about Samsung’s battery woes.

The basics

The science behind phone battery fires is actually pretty simple, and fairly well understood. Much like the infamous exploding hoverboards, phones use lithium ion battery packs for their power, and it just so happens that the liquid swimming around inside most lithium ion batteries is highly flammable.

If the battery short-circuits — say, by puncturing the incredibly thin sheet of plastic separating the positive and negative sides of the battery — the puncture point becomes the path of least resistance for electricity to flow.

It heats up the (flammable!) liquid electrolyte at that spot. And if the liquid heats up quickly enough, the battery can explode.

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Above: what happens when you puncture a phone’s battery.

The Galaxy Note 7 certainly isn’t the first phone to catch on fire, or even the first giant recall. By 2004, a spike in cell phone battery explosions prompted this CNET article. In 2009, Nokia recalled 46 million phone batteries that were at risk of short-circuiting. Exploding phones have even killed people.

No brand or model is necessarily safe: for instance, unlucky iPhone owners allegedly suffered nasty burns from exploding devices in 2015 and 2016. And though the Galaxy Note 7 is making headlines right now, other Samsung phones have also burst into flames, like the Galaxy Core that allegedly burned a 6-year-old child earlier this week.

We’ve known for years that lithium ion batteries pose a risk, but the electronics industry continues to use the flammable formula because the batteries are so much smaller and lighter than less-destructive chemistries. Lithium ion batteries pack a punch, for better or for worse.

Statistically small

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.

The FAA is strongly warning passengers not to use or charge a Note 7 on a plane, and many airlines are explicitly banning their use.

Donald Sadoway

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.)

Update, September 15 at 2:00p.m. PT: Updated tally with official US incident count from the Consumer Product Safety Commission.

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.

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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.

Samsung’s Note 7 battery holds an impressive 3,500mAh, despite its slim profile.


“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.

Why didn’t the phones catch fire immediately?

When Sadoway explains these theories, one thing doesn’t seem to add up. Today’s cell phone batteries generally charge faster (and get hotter) when they’re first plugged into the wall, not at the end when they’re trickle-charging the last few percent to reach their maximum capacity.

But these Note 7 phones didn’t explode right away. In practically every reported instance of a Note 7 catching fire or exploding, it happened after the phone was plugged in and left charging, sometimes overnight.

Then, there’s the little matter of how Samsung plans to make these phones safer — by issuing a firmware update that keeps the Galaxy Note 7 from charging to more than 60 percent of its full capacity. How could that possibly help, if things heat up the moment a phone is plugged into the wall?

Sadoway has a theory — albeit one without proof. What if only part of the battery was squished improperly, so that the phone couldn’t tell when it was 100 percent charged, and kept on charging the cell?

When lithium ion batteries are continually trickle charged, the lithium ions can start to cover the surface of the negative contact in a coating of lithium metal through a process called “plating.” And in extreme conditions, that lithium metal can form tiny spikes (called “dendrites”) that can poke right through the separator, creating — you guessed it — a short circuit.

That would seem to line up with the “variations in tension” Samsung says it found inside the defective battery cells.

“My guess is by backing off to 60 percent charge, they’ll be well below the threshold where these things happen,” says Sadoway. “Imagine we’re trying to fill our gas tank, we don’t have a really good regulator, and we don’t want to spill the gas all over our shoes. We want to make sure we’re cutting off the flow well before this thing gets to overflow conditions.”

Samsung didn’t immediately respond when asked for comment on the theory.

What happens next

These are just a few theories based on one battery expert’s remote analysis of Samsung’s initial findings. We don’t have the whole truth yet, and the truth is what Samsung and government agencies around the world are looking for as we speak. Organizations like the US Consumer Product Safety Commission have officially stepped in to recall the Galaxy Note 7 and figure out what happened.

But that could take time. It took six months for the CPSC to complete its investigation into hoverboard battery fires, to give you some idea.

For you, what happens now is simple: you should return or exchange your phone. If you live in the United States, you won’t have to wait much longer to get a new Note 7. Now that the CPSC has approved Samsung’s exchange program, you should be able to walk into a retail store by September 21, at the latest, and get a new Note. (You should probably call your carrier to get more specific info.)

We’ve confirmed that the replacement Notes will have a battery from a different supplier, in case you’re curious. (The manufacturing issues were found in batteries built by Samsung SDI.)

If you don’t want a Note 7, you can exchange it for one of Samsung’s other top smartphones, plus some cash for your trouble. Or, get a refund and use it to buy one of these excellent alternatives.

And if you don’t, you may soon be stuck with a Note 7 with dramatically reduced battery life. Don’t think you won’t: Samsung has strong relationships with US cellular carriers, and those carriers can force phones to update their firmware remotely.

Besides, it’s just the right thing to do. Only you can stop cell phone fires.

Update, September 15 at 2:00p.m. PT: The CPSC has officially approved the Galaxy Note 7 recall and exchange program in the United States, and Samsung says new Note 7 smartphones with safe batteries will be available at “most retail locations no later than September 21, 2016.” We’ve updated this story to reflect that.


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