Why lithium-ion batteries catch fire

Posted on by Duncan Geere

Samsung's Galaxy Note 7 is only the latest in a long line of gadgets spontaneously catching fire. Even the systems used in planes aren't immune. But there's one thing all of those gadgets tend to have in common - a lithium-ion battery.

To understand why those batteries keep catching fire, first you need to understand how a lithium-ion battery works. On each end there's an electrode - one is positive (the anode) and the other is negative (the cathode). In between is a liquid called an electrolyte. When charging, the lithium ions move to the anode, and when discharging they move to the cathode. Pretty simple.

Moving too fast

The problem comes when they move too fast. The rate at which lithium-ion batteries charge is carefully limited so that the lithium doesn't move too quickly - which, incidentally, is why batteries take time to charge. 

If it moves too fast, lithium plates begin to form around the anode, creating a short circuit and generating heat. That heat, if it builds up, can ignite the flammable electrolyte, and you've got a battery fire.

That's not the only thing that can cause a short circuit. If, during the manufacturing process, small holes are created or fragments of metal are left behind in the casing, then the same thing can happen. So too can stabbing a battery with a knife. The greater number of cells used in newer devices increases the chance of a failure.

It's all about the electrolytes

Quality controls in battery factories prevent this from happening too often, but occasionally there's something they miss. Samsung hasn't yet said what's causing the fires seen in the Galaxy Note 7, but it's investigating, ultimately leading to the Note 7 to be shelved for good.

In the meantime, chemists are working on developing new types of battery that aren't quite so explosive. Automatic shutdown designs, non-flammable electrolytes and more efficient alternative materials are all in development, to a greater or lesser extent.

Re-rewind

So don't worry - safer batteries are on the way. But for now, it's probably wise to check the battery in your smoke alarm from time to time, and keep one eye on your charging devices.

Jay Whitacre, a professor of materials science and engineering at Carnegie Mellon University, told Wired in 2015: "There is no way to tell when buying, since the catastrophic failure likely will not manifest until the battery is fully charged and discharged several times."


Duncan Geere is TechRadar's science writer. Every day he finds the most interesting science news and explains why you should care. You can read more of his stories here, and you can find him on Twitter under the handle @duncangeere.

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Netherlands becomes first country with nationwide Internet of Things

Posted on by Duncan Geere
Netherlands becomes first country with nationwide Internet of Things

Many countries around the world are beginning to roll out the infrastructure that'll allow physical objects - cars, appliances, buildings and more - to collect and exchange data between themselves in a trend known as the "Internet of Things".

Now, the Netherlands has become the first country in the world to roll out a nationwide network dedicated specifically to this kind of data traffic. Telecoms group KPN has announced that its "LoRa" network is now available across the entire country.

While many devices use Wi-Fi or 3G networks to connect to the web, those options aren't always ideal. Wi-Fi is pretty short-range, while 3G and 4G require a lot of device power. LoRa is one of several low-power, long-range, wide-area alternatives.

Substantial Customer Interest

The first chunk of the network was rolled out in Rotterdam and The Hague in November, but KPN says that "substantial customer interest" allowed it to accelerate the roll-out across the whole country. The technology can piggyback on existing 2G, 3G and 4G phone masts, which just need an extra LoRa antenna and gateway added to function as part of the network.

The company says it already has deals to connect 1.5 million objects and believes that number will grow substantially now the nationwide network is online. Already, trials of the technology are underway with baggage handling at Schiphol airport in Amsterdam, depth sounding at the port of Rotterdam and rail switch monitoring at Utrecht Central station.

"As from today the KPN LoRa network is available throughout The Netherlands," KPN said in a statement. "This makes The Netherlands the first country in the world to have a nationwide LoRa network for Internet of Things (IoT) application."

  • Duncan Geere is TechRadar's science writer. Every day he finds the most interesting science news and explains why you should care. You can read more of his stories here, and you can find him on Twitter under the handle @duncangeere.

‘Talking like a parent’ could be the best way to encrypt your emails

Posted on by Duncan Geere
'Talking like a parent' could be the best way to encrypt your emails

A security researcher from the Georgia Institute of Technology has invented an encryption system called "Open Book" that 'vaguifies' emails by removing specifics from them.

"It's kind of like when mom and dad are talking about potential vacation spots while the kids are nearby," said Eric Gilbert, who developed the software. "They can't say or spell 'Disney,' or the children will get too excited. So they use other words and the meaning is implied. Instead of 'Disney,' they could say 'have you bought tickets to the place yet.'"

He's built a Gmail plugin which works the same way - it pulls out specific words and replaces them with vague terms instead. The recipient should be able to work out what you're talking about from context, but anyone eavesdropping on the communications would fail to get the full message.

Typical Email Conversations

"As people react more with each other, they don't have to say as much to understand what is being said," said Gilbert. "Open Book uses the same technique. Even though the messages resemble typical email conversations, they're lost in the background noise of the Internet."

During small-scale tests, the recipients were able to correctly work out the missing words and phrases 95% of the time, while only 2% of strangers were able to do the same thing.

While you can't download it and have a go yet, you can go read the paper that Gilbert presented to the ACM Conference on Human Factors in Computing Systems in South Korea earlier this year.










Why your phone might one day tell you that you’re pregnant

Posted on by Duncan Geere
Why your phone might one day tell you that you're pregnant

German researchers have hacked together a fiber-optic sensor that uses a smartphone's flash and camera to perform a variety of biomolecular tests, including pregnancy diagnosis.

It works using a phenomenon called 'surface plasmon resonance', which is when light jiggles around the electrons on the surface of a thin metallic film in contact with a fluid. From the way the electrons jiggle, it's possible to work out the composition of that fluid, or the presence of particular molecules or gases.

Normally the process needs bulky lab equipment, but the team from the Hanover Centre for Optical Technologies managed to slim it down to something that'd fit on the rear side of a smartphone.

The flash provides the light through a fiber-optic cable, and the reflection is then carried to the camera through a diffraction grating that splits it into its component colours. From the way the brightness of the colours differs, it's possible to tell what's in the liquid.

Ubiquitous

Tests showed that the device's sensitivity is comparable to the aforementioned bulky lab equipment, despite the tiny device coming in at a fraction of the cost.

As well as letting researchers perform more complex analysis in the field, it could eventually allow smartphone owners to diagnose pregnancy or monitor diabetes - though we're still some way away from that point.

"We have the potential to develop small and robust lab-on-a-chip devices for smartphones," said Kort Bremer, who invented the technique. "So, surface plasmon resonance sensors could become ubiquitous now."

The device was detailed in a paper in Optics Express.










Processors do grow on trees: your next phone could be made of wood

Posted on by Duncan Geere
Processors do grow on trees: your next phone could be made of wood

Engineers hunting for a way to make electronics more sustainable have hit on a novel invention - a semiconductor chip made almost entirely out of wood.

The idea is that instead of making chips from petroleum-based plastic, we'd be able to use cellulose nanofibril - a flexible, biodegradable material that's made from plants. "The majority of material in a chip is support. We only use less than a couple of micrometers for everything else," said Zhenquang Ma, who lead the team.

The researchers have been studying bio-based polymers for more than a decade. While they showed some promise, there were a couple of key problems - wood's rough surface, and how it responds to moisture and heat.

"You don't want it to expand or shrink too much. Wood is a natural hydroscopic material and could attract moisture from the air and expand," said Zhiyong Cai, who also contributed to the discovery. "With an epoxy coating on the surface of the [material], we solved both the surface smoothness and the moisture barrier."

The result is a bio-based chip, which is not only flexible enough to use in consumer electronics but an order of magnitude more environmentally-friendly. "The chips are so safe you can put them in the forest and fungus will degrade it. They become as safe as fertilizer," said Ma.

He added: "Mass-producing current semiconductor chips is so cheap, and it may take time for the industry to adapt to our design. But flexible electronics are the future, and we think we're going to be well ahead of the curve."

The research was published in Nature Communications.


How a crying baby might soon power your phone

Posted on by Duncan Geere
How a crying baby might soon power your phone

Nanotechnologists at the Georgia Institute of Technology have made a microphone out of paper that could boost phone battery life using 'wasted' sound energy.

The team, led by Zhong Wang, used a laser to burn miniscule holes in a sheet of paper the size of a postage stamp, then coated one side in copper and the other with polytetrafluoroethylene - better known outside the chemistry world as the coating on non-stick pans. The two sides were joined on one edge, but left free on the others.

Sound waves, as you might remember from your physics classes, are made up of vibrations in the air. As they hit the sheet of paper, they cause the copper and Teflon sides to come into and out of contact, generating a small amount of static electricity like rubbing a balloon on your head.

Sounding good to us

That electricity - about 121 milliwatts per square metre - can then be harvested and used for whatever you like. Wang suggested its use in a mobile phone, but the trickle of power is far too low to charge most modern handsets - it'd merely extend battery life a small amount instead.

Still, Wang also suggests it could be used in military surveillance, sound recording, or jet engine noise reduction.

Us? We'd like to see it used to power a pair of noise-cancelling headphones so the screaming child two rows behind us on a plane is actually doing something useful.

The team's research was published in ACS Nano.