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A Samsung Galaxy Note 7 phone caught fire on 9 Oct., two days before Samsung Electronics announced that it is permanently discontinuing production of that model.

What's Behind Samsung's Phone Fires?

There’s never a good time for a corporation to get a black eye, but now is a particularly bad time for Korea’s Samsung. The company’s recall of 2.5 million Galaxy Note 7 smartphones, and its shutdown of sales and production also call attention to its recent recalls of other, unrelated products.

“What was remarkable here was that this was the world’s leading company for batteries and for consumer electronics,” says Cosmin Laslau, an electrochemistry expert and technology analyst for Lux Research. “It doesn’t get much more high profile than this.”

Though only 35 fires have been reported so far, one’s enough to ruin your whole day. A single blazing battery grounded a fleet of Boeing 787 Dreamliners some years back—one reason why in September, air safety regulators told people to shut off their Galaxy phones before packing them for a flight.

Right now, nobody in or out of Samsung really knows what’s going on. Investigations of the fires are still unpublished, but today Bloomberg News reports that Samsung has told Korea’s technology standards agency that the problem may involve a manufacturing error. According to that confidential note, the error brought negative and positive poles into contact, causing a short circuit. Samsung SDI Co. was the main battery supplier for the Galaxy Note 7, Bloomberg adds. 

Amperix Technology Limited has also provided some batteries for Samsung’s phone. If all the bad batteries had been in one batch, switching from one supplier to the other should have solved the problem—but it didn’t. “The chances that two suppliers are having similar issues are very low, so there must be more to the story,” Laslau says.

Why didn’t more of the phones burst into flames? And why didn’t the problem emerge right away? Does fire result only when you get a perfect storm of mishaps in several elements of the phone?

The random and rare nature of the fires doesn’t look like what you’d get from a straightforward manufacturing problem, says Bor Yann Liaw, a materials scientist who specializes in batteries at the Idaho National Laboratory, in Idaho Falls. “It is unlikely a [battery] design flaw either, since the products have been tested and have passed all safety requirements. This is probably a system design flaw that causes battery charging to derail from the normal process.”

“It could be a lot of things,” Laslau says. “A production process with impurities, or something to do with the separator [a membrane that prevents the electrodes from coming into contact, causing a short circuit]. Or the batteries could be fine but the energy management system could be charging them too aggressively.”

You can tweak any or all of these elements, but if you do, you’ll sacrifice performance and cost. Any supplier that did that would risk losing the contract to the next guy. 

“A lot of suppliers of batteries are under pressure to charge faster and pack in a lot more specific energy than ever before,” Laslau says. “Where is the tipping point where a major developer will say it will increase its price by 10 to 20 percent in order to make the batteries safer? This may force that type of introspection in the industry.”

This post was corrected on 17 October to clarify a statement about design flaws.

Photograph of solar-cell coated window

Quantum-Dot Coating Could Pull Solar Energy From Your Windows

In big cities, sometimes buildings that don’t have a lot of roof space for solar cells still have large windows that could harness light for electricity. Researchers at the Los Alamos National Laboratory, in New Mexico, reported yesterday in Nature Energy that a thin film of quantum dots on everyday glass could be the key to achieving acceptable efficiency in window photovoltaic systems at low cost.

Mostly, engineers have tried using modules of connected solar cells to capture sunlight falling on windows. Some wondered if it would be possible to do it with less cells. Taking advantage of a mechanism for capturing the light falling on a window and then directing it to a single solar cell “simplifies the device; it makes it less expensive,” says Victor Klimov, a nanotechnology engineer at Los Alamos.

At first, engineers tried using organic dyes as a way to concentrate the light. The problem with that, Klimov says, is that the dyes absorb the light they produce because it appears very similar to the incoming rays from the sun. In 2013, engineers instead started investigating nanometer-scale semiconductors called quantum dots because they allow customizing properties such as what kinds of light they absorb and which ones they don’t.

In the new research, Klimov and his team found that a thin layer of quantum dots on normal glass could have a lifetime of up to 14 years and about 1.9 percent overall energy conversion efficiency. To make these devices practical they’ll have to reach 6 percent, he says, so they’re getting close.

What’s more, adding quantum dots to window glass is surprisingly easy: A machine pours a slurry of quantum dots and PVP polymer onto the glass and a blade spreads it out to form a thin sheet.

The quantum dots consist of a CdSe inner core, a Cd1−xZnxS outer shell, and are coated in silica for protection from oxidation—with the outer shell acting like an absorber. When a photon hits a dot, an electron in the shell is kicked out of its valence band into the conduction band, leaving a hole. The rogue electron and hole jump to the core, where they recombine to produce a new photon with lower energy.

By design, the shell only absorbs high energy photons, and the new photon from the core is free to propagate throughout the glass and quantum dot layers via internal reflections. Eventually, the propagating photons would arrive at the glass edges—where one or more solar cells could pick them up.

In 2015 research, members of the team had tried dispersing quantum dots directly inside a polymer. However, in polymer materials such as this, many of these photons would scatter and escape the material. The optical properties of the new thin quantum-dot layer on glass are such that there’s minimal scattering and the light tends to propagate much longer, Klimov says.

“This is important for showing that these nanocrystals may be used to make large-area and cost-effective diffuse light concentrators,” Vivian Ferry, an energy and electronics researcher at the University of Minnesota who was not involved in the study, but has worked with solar cells and quantum dots, writes in an email. 

When the researchers tested absorption and stability properties, they also found the manufactured device held its own.

“If you’re serious about applications,” Klimov says, “Stability must be comparable to the stability of the solar cell.”

He believes the application technique is inexpensive and accessible enough for the glass industry to use. A coating could even be scraped off and re-used.

Still, there’s plenty of work to do before reaching the break-even point on energy conversion, he says. To meet the efficiency goal, he’s now tinkering with the concentrations of quantum dots used and their absorption properties.

For comparable light concentrators of a similar size, color, and transparency, the Los Alamos system is “pretty good,” writes David Patrick, an energy researcher at Western Washington University who was not involved in the study but has worked on solar light conversion. 

A correction to this article was made on 11 October 2016. The inner core and outer shell materials were inadvertently reversed.

perovskite solar cell

Perovskites Become More Stable

Solar cells based on perovskite crystals have made unparalleled advances in performance in the past decade, but most research on these devices has neglected the question of how stable they might be outdoors for long periods of time. Now two research groups have come up with different ways to improve perovskite solar cell stability, findings detailed in two papers in the journal Science.

One approach added rubidium cations to perovskite. "We believe this may help to relax lattice strain, resulting in a more defect-free overall crystal," says Michael Saliba, lead author of that study and a solar cell researcher at the Swiss Federal Institute of Technology in Lausanne.

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a perovskite solar cell made of many layers

Perovskite Solar Cells Grow Better With a Dash of Acrylic Glass

The conversion efficiency of solar cells based on perovskite crystals has shot up from 3.8 to 22.1 percent in less than a decade, an unprecedented rise in the field of photovoltaics. "Perovskites have rocked the whole photovoltaic community," says Michael Grätzel, director of the École Polytechnique Fédérale de Lausanne’s Laboratory of Photonics and Interfaces. Trying to keep the progress going, he and his colleagues have found a way to grow bigger, better performing perovskite cells—by growing with ordinary acrylic glass.

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Map of Asia Super Grid

Trio of Nations Aims to Hook Asia Super Grid to Grids of the World

Northeast Asia, the region encompassing China, South Korea, and Japan, has not yet gotten around to connecting its electricity grids together. But that’s not stopping these countries from promoting the Asia Super Grid, calculated to become the center of a global energy grid providing abundant, cheap electricity based on renewable energy. 

In Japan, the idea emerged following the 2011 Tohoku earthquake and subsequent Fukushima Daiichi nuclear plant disaster. The possibility of a nuclear disaster so shocked Masayoshi Son, founder and head of the telecom and Internet giant SoftBank Group, that he established the Renewable Energy Institute soon after to help develop and promote renewable energy.

“I was a total layman (in renewable energy) at the time of the earthquake,” Son told a packed audience attending a symposium celebrating the fifth anniversary of the institute in Tokyo last Friday.

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A patch of energy harvesting fabric combines solar-cell threads and triboelectric energy generator fibers

Walk Around in the Sun to Power Wearables With This Cloth

A new wearable fabric that generates electricity from both sunlight and motion could let you power your cell phone or smart watch by walking around outside. Researchers made the textile by weaving together plastic fiber solar cells and fiber-based generators that produce electricity when rubbed against each other.

The 0.32-millimeter-thick fabric is lightweight, flexible, breathable, and uses low-cost materials, its creators say. It could be integrated into clothes, tents, and curtains, turning them into power sources when they flap or are exposed to the sun. By harvesting solar and mechanical energy, the power-generating cloth could work day and night, its inventors say.

“The hybrid power textile could be extensively applied not only to self-powered electronics but also possibly to power generation on a larger scale,” Zhong Lin Wang at Georgia Tech, Xing Fan at Chongqing University in Chongqing, China, and their colleagues write in a research published today in the journal Nature Energy.

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Tapiwa M. Chiwewe is a research scientist at IBM Research in Johannesburg, South Africa, where he and colleagues are expanding the company's machine learning technology to predicting air quality.

Tackling Air Quality Prediction in South Africa With Machine Learning

Machine learning is nipping at the heels of conventional physical modeling of air quality predictions in more and more places. The latest is Johannesburg, South Africa, where computer engineer Tapiwa M. Chiwewe at the newly opened IBM Research lab is adapting IBM’s air quality prediction software to local needs and adding new capabilities. The work is an expansion of the so-called Green Horizons initiative, in which IBM researchers partnered with Chinese government researchers and officials, starting two years ago.

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A transient battery hooked to a multimeter by alligator clips shows an output of 2.5 volts.

This Battery Will Self-Destruct in 30 Minutes

Electronics that self-destruct over time could be the key to military applications to help keep secrets out of enemy handsmedical implants that don't need surgical removal, and environmental sensors that melt away when no longer needed. Now scientists at Iowa State University say they have developed the first practical transient battery to power them.

Recently, scientists have developed a wide range of transient electronics that can perform a variety of functions until exposure to light, heat, or liquids triggers their self-destruction. Until now, however, these devices largely relied on external power sources that were not transient themselves.

Early research into transient batteries led to devices with limited power, stability, and shelf life. They were also slow to destroy themselves, says Reza Montazami, a materials scientist at Iowa State University who led the effort to invent a better transient battery. Now Montazami and his colleagues have developed a transient battery that can power a desktop calculator for about 15 minutes and destroy itself in about 30 minutes.

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A schematic of the device

Electrochemical Cell Makes Electricity and Chemicals From CO2

Using aluminum and oxygen, new technology can convert carbon dioxide into useful chemicals and also generate substantial amounts of electrical energy, researchers say.

The large-scale adoption of carbon capture, utilization and sequestration (CCUS) technologies is currently limited in part by how much energy it can take to capture carbon. In addition, methods to make the most of carbon dioxide once it gets stored by converting it into useful chemicals and fuels have proven difficult to develop.

But recently, chemical engineer Lynden Archer and his colleagues at Cornell University investigated whether electrochemical cells could both capture carbon dioxide and generate power. Such electrochemical cells, they hypothesized, would use a metal as the anode and mixed streams of carbon dioxide and oxygen as the active ingredients of the cathode. The electrochemical reactions between the anode and the cathode would sequester the carbon dioxide into carbon-rich compounds while also producing electricity.

Archer and his colleague Wajdi Al Sadat detailed their findings in the 20 July online edition of the journal Science Advances.

Previous research used lithium, sodium, and magnesium as the anodes in such electrochemical cells. These converted carbon dioxide into carbonates, “which are not that useful,” Archer says. “It then occurred to us to use aluminum, which is the third most abundant element in Earth's crust.” Aluminum's abundance makes it cheap, and it is also less chemically reactive than lithium and sodium, which makes it safer to work with, Archer adds.

In the new device, the anode consists of aluminum foil, the cathode consists of a porous, electrically conductive material such as a stainless steel mesh that allows carbon dioxide and oxygen to pass through it, and the electrolyte bridging the anode and cathode is a liquid through which molecules can diffuse.

In experiments, the electrochemical cell could generate as much as 13 ampere-hours for each gram of carbon it captured, without the need for a catalyst or high temperatures. Moreover, it converted carbon dioxide into aluminum oxalate, which, in turn, is easily converted into oxalic acid, a chemical widely used in industry. “It's a versatile product that's a nice starting material for plastics and so forth,” Archer says. In theory, adding extra compounds to the cathode might help convert carbon dioxide to other useful chemicals, Archer adds.

Archer notes that the electrolyte in his group’s electrochemical cell does not work if exposed to water. This is a problem because the carbon dioxide emissions that this device might treat, such as those from factories or power plants, might be loaded with moisture. However, it might be possible to find an electrolyte that is much less sensitive to water, Archer says.

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