Early Friday morning, Samsung officially recalled millions of its popular new Galaxy Note 7 smartphones. The reason sounds like it belongs more in a Tex Avery cartoon than our reality: dozens of reports of devices overheating, burning, and even exploding.

The culprit, as is always the case with this sort of thing, is the battery. It’s why the Note 7 went haywire, why hoverboards have always been a dangerous investment, why Boeing had to keep the 787 on the tarmac, and why every few months there seems to be another report of a smartphone or laptop going boom.

In fact, the Samsung incident is unusual only in scale, and in the company’s admirably aggressive response. Samsung hasn’t said specifically what’s causing the issue, but experts say it could have been any number of things. After all, that’s just what lithium ion batteries do. Well, bad ones, anyway.

Battery Pack

To understand why lithium ion batteries keep causing trouble, we’re going to need to do a very quick overview of how they work. They have three main components: an anode at one end, a cathode at the other, and an electrolyte between them. A voltage runs across it, driving lithium ions from one end to the other for charging and discharging.

The vast majority of the time, that process goes off without complications. But when complications do happen, it can get very bad, very quickly.

“There are a couple of dangerous things that can happen,” says George Crabtree, director of the Joint Center for Energy Storage Research at Argonne National Lab. “One is that you can overcharge, and that leads to heating, and can lead to unwanted chemical reactions in the anode.” The problem can occur going the other direction, during discharge, as well. The cathode contains oxide, Crabtree says, which can combine with organic materials in the electrolyte and release heat. A “low-quality” battery, one where impurities sneak in, can also be responsible for unpredictable results.

If you think “unwanted chemical reactions” has an ominous ring to it, you’re not wrong, especially when they result in what’s known as a thermal runaway. “So much heat is released that it spirals up, the temperature goes higher, that makes the reaction go faster,” says Crabtree. “That’s the one that everybody worries about.”

That’s because it’s the one that ends with a fire in your pocket. Once the exothermic reaction hits around 150 degrees Celsius, it just keeps going, until something catches on fire.

These issues also aren’t necessarily the first time you plug a smartphone in; they can develop over time. “You might get batteries that just aren’t as robust through many charge and discharge cycles,” says Crabtree. “A tiny reaction that takes place due to some composition error in the electrolyte or the electrode starts to mount up. Pretty soon, you have a serious reaction.”

And there’s more! More things that can go wrong, more reactions that lead to destruction. Without diving much deeper into the chemistry, the simple fact is that lithium ion batteries are complicated, and getting them wrong has serious consequences.

Lowering the Boom

Obviously, battery-makers know this. Samsung knows this. And Samsung’s suppliers also know it, which is why they had safety mechanisms in place to keep it from happening.

“In the battery itself, there’s a chip that’s the protection circuit that’s designed to prevent this kind of thing,” says Kyle Wiens, co-founder and CEO of iFixit, an online repair community and parts retailer. (Weins is also an occasional WIRED contributor.) iFixit recently performed a teardown of the Galaxy Note 7, in which it took the device apart to inspect all of its internals.

It’s clear the existing safety measures aren’t quite foolproof.

Nothing about that process jumped out at Wiens as necessarily causing or contributing to the overheating issue. Wiens says there are some potential red flags; it’s a high-voltage battery, for one, and the glass back doesn’t dissipate heat as well as metal might. But there’s no reason to think those are central to the problem, especially since similar smartphones haven’t similarly combusted.

“There’s nothing really new about the Note 7 that’s dramatically different from previous versions,” says Weins.

At some point, then, regardless of whatever the chemical underpinnings, it seems likely that the protection circuit didn’t do its job, which is to shut the battery down once it reaches a certain temperature. But even that’s hard to say with certainty. For one, Samsung hasn’t commented on the specific cause, other than to say it is a “battery cell issue.” For another, the company likely sourced batteries from several vendors. We don’t know which provided the faulty batteries; we just know that the recall applies to all Note 7s sold outside of China.

Regardless, it’s clear the existing safety measures aren’t quite foolproof. That doesn’t mean, though, that we’re fated to a lifetime of battery boom-times.

“Take the case of gasoline,” says Crabtree. “We like it because we can combust it and get a lot of energy out of it and drive our cars with it. The same reason that we like it is why it’s dangerous.”

That’s not so of lithium-ion batteries. Their combustibility isn’t inherent to their value; it’s a side reaction that no one wants. “In principle,” says Crabtree, “you could design a battery that didn’t have those side reactions.”

There’s already progress being made in that direction. Earlier this year, researchers at Stanford published a study that proposed a passive method of shutting down batteries when temperatures rise, a membrane that gradually expands when things get hot until it’s big enough to shut off current to the cathode. It’s always going to be a tradeoff between effectiveness and safety, but it’s an increasingly narrower one.

“There’s a tension between how much energy you can pack into a small space in the safety,” says Weins. “Which is why most of the effort that goes into these batteries is around the safety side of it.”

That doesn’t help Note 7 owners. But at least the future has the chance to be significantly less explosive than today.

Read more: http://www.wired.com/2016/09/smartphones-still-blow/

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