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    Engineers solve a mystery on the path to smaller, lighter batteries

    A discovery by MIT researchers could finally unlock the door to the design of a new kind of rechargeable lithium battery that is more lightweight, compact, and safe than current versions, and that has been pursued by labs around the world for years.

    The key to this potential leap in battery technology is replacing the liquid electrolyte that sits between the positive and negative electrodes with a much thinner, lighter layer of solid ceramic material, and replacing one of the electrodes with solid lithium metal. This would greatly reduce the overall size and weight of the battery and remove the safety risk associated with liquid electrolytes, which are flammable. But that quest has been beset with one big problem: dendrites.

    Dendrites, whose name comes from the Latin for branches, are projections of metal that can build up on the lithium surface and penetrate into the solid electrolyte, eventually crossing from one electrode to the other and shorting out the battery cell. Researchers haven’t been able to agree on what gives rise to these metal filaments, nor has there been much progress on how to prevent them and thus make lightweight solid-state batteries a practical option.

    The new research, being published today in the journal Joule in a paper by MIT Professor Yet-Ming Chiang, graduate student Cole Fincher, and five others at MIT and Brown University, seems to resolve the question of what causes dendrite formation. It also shows how dendrites can be prevented from crossing through the electrolyte.

    Chiang says in the group’s earlier work, they made a “surprising and unexpected” finding, which was that the hard, solid electrolyte material used for a solid-state battery can be penetrated by lithium, which is a very soft metal, during the process of charging and discharging the battery, as ions of lithium move between the two sides.

    This shuttling back and forth of ions causes the volume of the electrodes to change. That inevitably causes stresses in the solid electrolyte, which has to remain fully in contact with both of the electrodes that it is sandwiched between. “To deposit this metal, there has to be an expansion of the volume because you’re adding new mass,” Chiang says. “So, there’s an increase in volume on the side of the cell where the lithium is being deposited. And if there are even microscopic flaws present, this will generate a pressure on those flaws that can cause cracking.”

    Those stresses, the team has now shown, cause the cracks that allow dendrites to form. The solution to the problem turns out to be more stress, applied in just the right direction and with the right amount of force.

    While previously, some researchers thought that dendrites formed by a purely electrochemical process, rather than a mechanical one, the team’s experiments demonstrate that it is mechanical stresses that cause the problem.

    The process of dendrite formation normally takes place deep within the opaque materials of the battery cell and cannot be observed directly, so Fincher developed a way of making thin cells using a transparent electrolyte, allowing the whole process to be directly seen and recorded. “You can see what happens when you put a compression on the system, and you can see whether or not the dendrites behave in a way that’s commensurate with a corrosion process or a fracture process,” he says.

    The team demonstrated that they could directly manipulate the growth of dendrites simply by applying and releasing pressure, causing the dendrites to zig and zag in perfect alignment with the direction of the force.

    Applying mechanical stresses to the solid electrolyte doesn’t eliminate the formation of dendrites, but it does control the direction of their growth. This means they can be directed to remain parallel to the two electrodes and prevented from ever crossing to the other side, and thus rendered harmless.

    In their tests, the researchers used pressure induced by bending the material, which was formed into a beam with a weight at one end. But they say that in practice, there could be many different ways of producing the needed stress. For example, the electrolyte could be made with two layers of material that have different amounts of thermal expansion, so that there is an inherent bending of the material, as is done in some thermostats.

    Another approach would be to “dope” the material with atoms that would become embedded in it, distorting it and leaving it in a permanently stressed state. This is the same method used to produce the super-hard glass used in the screens of smart phones and tablets, Chiang explains. And the amount of pressure needed is not extreme: The experiments showed that pressures of 150 to 200 megapascals were sufficient to stop the dendrites from crossing the electrolyte.

    The required pressure is “commensurate with stresses that are commonly induced in commercial film growth processes and many other manufacturing processes,” so should not be difficult to implement in practice, Fincher adds.

    In fact, a different kind of stress, called stack pressure, is often applied to battery cells, by essentially squishing the material in the direction perpendicular to the battery’s plates — somewhat like compressing a sandwich by putting a weight on top of it. It was thought that this might help prevent the layers from separating. But the experiments have now demonstrated that pressure in that direction actually exacerbates dendrite formation. “We showed that this type of stack pressure actually accelerates dendrite-induced failure,” Fincher says.

    What is needed instead is pressure along the plane of the plates, as if the sandwich were being squeezed from the sides. “What we have shown in this work is that when you apply a compressive force you can force the dendrites to travel in the direction of the compression,” Fincher says, and if that direction is along the plane of the plates, the dendrites “will never get to the other side.”

    That could finally make it practical to produce batteries using solid electrolyte and metallic lithium electrodes. Not only would these pack more energy into a given volume and weight, but they would eliminate the need for liquid electrolytes, which are flammable materials.

    Having demonstrated the basic principles involved, the team’s next step will be to try to apply these to the creation of a functional prototype battery, Chiang says, and then to figure out exactly what manufacturing processes would be needed to produce such batteries in quantity. Though they have filed for a patent, the researchers don’t plan to commercialize the system themselves, he says, as there are already companies working on the development of solid-state batteries. “I would say this is an understanding of failure modes in solid-state batteries that we believe the industry needs to be aware of and try to use in designing better products,” he says.

    The research team included Christos Athanasiou and Brian Sheldon at Brown University, and Colin Gilgenbach, Michael Wang, and W. Craig Carter at MIT. The work was supported by the U.S. National Science Foundation, the U.S. Department of Defense, the U.S. Defense Advanced Research Projects Agency, and the U.S. Department of Energy. More

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    With new heat treatment, 3D-printed metals can withstand extreme conditions

    A new MIT-developed heat treatment transforms the microscopic structure of 3D-printed metals, making the materials stronger and more resilient in extreme thermal environments. The technique could make it possible to 3D print high-performance blades and vanes for power-generating gas turbines and jet engines, which would enable new designs with improved fuel consumption and energy efficiency.

    Today’s gas turbine blades are manufactured through conventional casting processes in which molten metal is poured into complex molds and directionally solidified. These components are made from some of the most heat-resistant metal alloys on Earth, as they are designed to rotate at high speeds in extremely hot gas, extracting work to generate electricity in power plants and thrust in jet engines.

    There is growing interest in manufacturing turbine blades through 3D-printing, which, in addition to its environmental and cost benefits, could allow manufacturers to quickly produce more intricate, energy-efficient blade geometries. But efforts to 3D-print turbine blades have yet to clear a big hurdle: creep.

    In metallurgy, creep refers to a metal’s tendency to permanently deform in the face of persistent mechanical stress and high temperatures. While researchers have explored printing turbine blades, they have found that the printing process produces fine grains on the order of tens to hundreds of microns in size — a microstructure that is especially vulnerable to creep.

    “In practice, this would mean a gas turbine would have a shorter life or less fuel efficiency,” says Zachary Cordero, the Boeing Career Development Professor in Aeronautics and Astronautics at MIT. “These are costly, undesirable outcomes.”

    Cordero and his colleagues found a way to improve the structure of 3D-printed alloys by adding an additional heat-treating step, which transforms the as-printed material’s fine grains into much larger “columnar” grains — a sturdier microstructure that should minimize the material’s creep potential, since the “columns” are aligned with the axis of greatest stress. The researchers say the method, outlined today in Additive Manufacturing, clears the way for industrial 3D-printing of gas turbine blades.

    “In the near future, we envision gas turbine manufacturers will print their blades and vanes at large-scale additive manufacturing plants, then post-process them using our heat treatment,” Cordero says. “3D-printing will enable new cooling architectures that can improve the thermal efficiency of a turbine, so that it produces the same amount of power while burning less fuel and ultimately emits less carbon dioxide.”

    Cordero’s co-authors on the study are lead author Dominic Peachey, Christopher Carter, and Andres Garcia-Jimenez at MIT, Anugrahaprada Mukundan and Marie-Agathe Charpagne of the University of Illinois at Urbana-Champaign, and Donovan Leonard of Oak Ridge National Laboratory.

    Triggering a transformation

    The team’s new method is a form of directional recrystallization — a heat treatment that passes a material through a hot zone at a precisely controlled speed to meld a material’s many microscopic grains into larger, sturdier, and more uniform crystals.

    Directional recrystallization was invented more than 80 years ago and has been applied to wrought materials. In their new study, the MIT team adapted directional recrystallization for 3D-printed superalloys.

    The team tested the method on 3D-printed nickel-based superalloys — metals that are typically cast and used in gas turbines. In a series of experiments, the researchers placed 3D-printed samples of rod-shaped superalloys in a room-temperature water bath placed just below an induction coil. They slowly drew each rod out of the water and through the coil at various speeds, dramatically heating the rods to temperatures varying between 1,200 and 1,245 degrees Celsius.

    They found that drawing the rods at a particular speed (2.5 millimeters per hour) and through a specific temperature (1,235 degrees Celsius) created a steep thermal gradient that triggered a transformation in the material’s printed, fine-grained microstructure.

    “The material starts as small grains with defects called dislocations, that are like a mangled spaghetti,” Cordero explains. “When you heat this material up, those defects can annihilate and reconfigure, and the grains are able to grow. We’re continuously elongating the grains by consuming the defective material and smaller grains — a process termed recrystallization.”

    Creep away

    After cooling the heat-treated rods, the researchers examined their microstructure using optical and electron microscopy, and found that the material’s printed microscopic grains were replaced with “columnar” grains, or long crystal-like regions that were significantly larger than the original grains.

    “We’ve completely transformed the structure,” says lead author Dominic Peachey. “We show we can increase the grain size by orders of magnitude, to massive columnar grains, which theoretically should lead to dramatic improvements in creep properties.”

    The team also showed they could manipulate the draw speed and temperature of the rod samples to tailor the material’s growing grains, creating regions of specific grain size and orientation. This level of control, Cordero says, can enable manufacturers to print turbine blades with site-specific microstructures that are resilient to specific operating conditions.

    Cordero plans to test the heat treatment on 3D-printed geometries that more closely resemble turbine blades. The team is also exploring ways to speed up the draw rate, as well as test a heat-treated structure’s resistance to creep. Then, they envision that the heat treatment could enable the practical application of 3D-printing to produce industrial-grade turbine blades, with more complex shapes and patterns.

    “New blade and vane geometries will enable more energy-efficient land-based gas turbines, as well as, eventually, aeroengines,” Cordero notes. “This could from a baseline perspective lead to lower carbon dioxide emissions, just through improved efficiency of these devices.”

    This research was supported, in part, by the U.S. Office of Naval Research. More

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    In nanotube science, is boron nitride the new carbon?

    Engineers at MIT and the University of Tokyo have produced centimeter-scale structures, large enough for the eye to see, that are packed with hundreds of billions of hollow aligned fibers, or nanotubes, made from hexagonal boron nitride.

    Hexagonal boron nitride, or hBN, is a single-atom-thin material that has been coined “white graphene” for its transparent appearance and its similarity to carbon-based graphene in molecular structure and strength. It can also withstand higher temperatures than graphene, and is electrically insulating, rather than conductive. When hBN is rolled into nanometer-scale tubes, or nanotubes, its exceptional properties are significantly enhanced.

    The team’s results, published today in the journal ACS Nano, provide a route toward fabricating aligned boron nitride nanotubes (A-BNNTs) in bulk. The researchers plan to harness the technique to fabricate bulk-scale arrays of these nanotubes, which can then be combined with other materials to make stronger, more heat-resistant composites, for instance to shield space structures and hypersonic aircraft.

    As hBN is transparent and electrically insulating, the team also envisions incorporating the BNNTs into transparent windows and using them to electrically insulate sensors within electronic devices. The team is also investigating ways to weave the nanofibers into membranes for water filtration and for “blue energy” — a concept for renewable energy in which electricity is produced from the ionic filtering of salt water into fresh water.

    Brian Wardle, professor of aeronautics and astronautics at MIT, likens the team’s results to scientists’ decades-long, ongoing pursuit of manufacturing bulk-scale carbon nanotubes.

    “In 1991, a single carbon nanotube was identified as an interesting thing, but it’s been 30 years getting to bulk aligned carbon nanotubes, and the world’s not even fully there yet,” Wardle says. “With the work we’re doing, we’ve just short-circuited about 20 years in getting to bulk-scale versions of aligned boron nitride nanotubes.”

    Wardle is the senior author of the new study, which includes lead author and MIT research scientist Luiz Acauan, former MIT postdoc Haozhe Wang, and collaborators at the University of Tokyo.

    A vision, aligned

    Like graphene, hexagonal boron nitride has a molecular structure resembling chicken wire. In graphene, this chicken wire configuration is made entirely of carbon atoms, arranged in a repeating pattern of hexagons. For hBN, the hexagons are composed of alternating atoms of boron and nitrogen. In recent years, researchers have found that two-dimensional sheets of hBN exhibit exceptional properties of strength, stiffness, and resilience at high temperatures. When sheets of hBN are rolled into nanotube form, these properties are further enhanced, particularly when the nanotubes are aligned, like tiny trees in a densely packed forest.

    But finding ways to synthesize stable, high quality BNNTs has proven challenging. A handful of efforts to do so have produced low-quality, nonaligned fibers.

    “If you can align them, you have much better chance of harnessing BNNTs properties at the bulk scale to make actual physical devices, composites, and membranes,” Wardle says.

    In 2020, Rong Xiang and colleagues at the University of Tokyo found they could produce high-quality boron nitride nanotubes by first using a conventional approach of chemical vapor deposition to grow a forest of short, few micron-long carbon nanotubes. They then coated the carbon-based forest with “precursors” of boron and nitrogen gas, which when baked in an oven at high temperatures crystallized onto the carbon nanotubes to form high-quality nanotubes of hexagonal boron nitride with carbon nanotubes inside.

    Burning scaffolds

    In the new study, Wardle and Acauan have extend and scale Xiang’s approach, essentially removing the underlying carbon nanotubes and leaving the long boron nitride nanotubes to stand on their own. The team drew on the expertise of Wardle’s group, which has focused for years on fabricating high-quality aligned arrays of carbon nanotubes. With their current work, the researchers looked for ways to tweak the temperatures and pressures of the chemical vapor deposition process in order to remove the carbon nanotubes while leaving the boron nitride nanotubes intact.

    “The first few times we did it, it was completely ugly garbage,” Wardle recalls. “The tubes curled up into a ball, and they didn’t work.”

    Eventually, the team hit on a combination of temperatures, pressures, and precursors that did the trick. With this combination of processes, the researchers first reproduced the steps that Xiang took to synthesize the boron-nitride-coated carbon nanotubes. As hBN is resistant to higher temperatures than graphene, the team then cranked up the heat to burn away the underlying black carbon nanotube scaffold, while leaving the transparent, freestanding boron nitride nanotubes intact.
    By using carbon nanotubes as a scaffold, MIT engineers grow forests of “white graphene” that emerge (in MIT pattern) after burning away the black carbon scaffold. Courtesy of the researchersIn microscopic images, the team observed clear crystalline structures — evidence that the boron nitride nanotubes have a high quality. The structures were also dense: Within a square centimeter, the researchers were able to synthesize a forest of more than 100 billion aligned boron nitride nanotubes, that measured about a millimeter in height — large enough to be visible by eye. By nanotube engineering standards, these dimensions are considered to be “bulk” in scale.

    “We are now able to make these nanoscale fibers at bulk scale, which has never been shown before,” Acauan says.

    To demonstrate the flexibility of their technique, the team synthesized larger carbon-based structures, including a weave of carbon fibers, a mat of “fuzzy” carbon nanotubes, and sheets of randomly oriented carbon nanotubes known as “buckypaper.” They coated each carbon-based sample with boron and nitrogen precursors, then went through their process to burn away the underlying carbon. In each demonstration, they were left with a boron-nitride replica of the original black carbon scaffold.

    They also were able to “knock down” the forests of BNNTs, producing horizontally aligned fiber films that are a preferred configuration for incorporating into composite materials.

    “We are now working toward fibers to reinforce ceramic matrix composites, for hypersonic and space applications where there are very high temperatures, and for windows for devices that need to be optically transparent,” Wardle says. “You could make transparent materials that are reinforced with these very strong nanotubes.”

    This research was supported, in part, by Airbus, ANSYS, Boeing, Embraer, Lockheed Martin, Saab AB, and Teijin Carbon America through MIT’s Nano-Engineered Composite aerospace STructures (NECST) Consortium. More

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    Simplifying the production of lithium-ion batteries

    When it comes to battery innovations, much attention gets paid to potential new chemistries and materials. Often overlooked is the importance of production processes for bringing down costs.

    Now the MIT spinout 24M Technologies has simplified lithium-ion battery production with a new design that requires fewer materials and fewer steps to manufacture each cell. The company says the design, which it calls “SemiSolid” for its use of gooey electrodes, reduces production costs by up to 40 percent. The approach also improves the batteries’ energy density, safety, and recyclability.

    Judging by industry interest, 24M is onto something. Since coming out of stealth mode in 2015, 24M has licensed its technology to multinational companies including Volkswagen, Fujifilm, Lucas TVS, Axxiva, and Freyr. Those last three companies are planning to build gigafactories (factories with gigawatt-scale annual production capacity) based on 24M’s technology in India, China, Norway, and the United States.

    “The SemiSolid platform has been proven at the scale of hundreds of megawatts being produced for residential energy-storage systems. Now we want to prove it at the gigawatt scale,” says 24M CEO Naoki Ota, whose team includes 24M co-founder, chief scientist, and MIT Professor Yet-Ming Chiang.

    Establishing large-scale production lines is only the first phase of 24M’s plan. Another key draw of its battery design is that it can work with different combinations of lithium-ion chemistries. That means 24M’s partners can incorporate better-performing materials down the line without substantially changing manufacturing processes.

    The kind of quick, large-scale production of next-generation batteries that 24M hopes to enable could have a dramatic impact on battery adoption across society — from the cost and performance of electric cars to the ability of renewable energy to replace fossil fuels.

    “This is a platform technology,” Ota says. “We’re not just a low-cost and high-reliability operator. That’s what we are today, but we can also be competitive with next-generation chemistry. We can use any chemistry in the market without customers changing their supply chains. Other startups are trying to address that issue tomorrow, not today. Our tech can address the issue today and tomorrow.”

    A simplified design

    Chiang, who is MIT’s Kyocera Professor of Materials Science and Engineering, got his first glimpse into large-scale battery production after co-founding another battery company, A123 Systems, in 2001. As that company was preparing to go public in the late 2000s, Chiang began wondering if he could design a battery that would be easier to manufacture.

    “I got this window into what battery manufacturing looked like, and what struck me was that even though we pulled it off, it was an incredibly complicated manufacturing process,” Chiang says. “It derived from magnetic tape manufacturing that was adapted to batteries in the late 1980s.”

    In his lab at MIT, where he’s been a professor since 1985, Chiang started from scratch with a new kind of device he called a “semi-solid flow battery” that pumps liquids carrying particle-based electrodes to and from tanks to store a charge.

    In 2010, Chiang partnered with W. Craig Carter, who is MIT’s POSCO Professor of Materials Science and Engineering, and the two professors supervised a student, Mihai Duduta ’11, who explored flow batteries for his undergraduate thesis. Within a month, Duduta had developed a prototype in Chiang’s lab, and 24M was born. (Duduta was the company’s first hire.)

    But even as 24M worked with MIT’s Technology Licensing Office (TLO) to commercialize research done in Chiang’s lab, people in the company including Duduta began rethinking the flow battery concept. An internal cost analysis by Carter, who consulted for 24M for several years, ultimately lead the researchers to change directions.

    That left the company with loads of the gooey slurry that made up the electrodes in their flow batteries. A few weeks after Carter’s cost analysis, Duduta, then a senior research scientist at 24M, decided to start using the slurry to assemble batteries by hand, mixing the gooey electrodes directly into the electrolyte. The idea caught on.

    The main components of batteries are the positive and negatively charged electrodes and the electrolyte material that allows ions to flow between them. Traditional lithium-ion batteries use solid electrodes separated from the electrolyte by layers of inert plastics and metals, which hold the electrodes in place.

    Stripping away the inert materials of traditional batteries and embracing the gooey electrode mix gives 24M’s design a number of advantages.

    For one, it eliminates the energy-intensive process of drying and solidifying the electrodes in traditional lithium-ion production. The company says it also reduces the need for more than 80 percent of the inactive materials in traditional batteries, including expensive ones like copper and aluminum. The design also requires no binder and features extra thick electrodes, improving the energy density of the batteries.

    “When you start a company, the smart thing to do is to revisit all of your assumptions  and ask what is the best way to accomplish your objectives, which in our case was simply-manufactured, low-cost batteries,” Chiang says. “We decided our real value was in making a lithium-ion suspension that was electrochemically active from the beginning, with electrolyte in it, and you just use the electrolyte as the processing solvent.”

    In 2017, 24M participated in the MIT Industrial Liaison Program’s STEX25 Startup Accelerator, in which Chiang and collaborators made critical industry connections that would help it secure early partnerships. 24M has also collaborated with MIT researchers on projects funded by the Department of Energy.

    Enabling the battery revolution

    Most of 24M’s partners are eyeing the rapidly growing electric vehicle (EV) market for their batteries, and the founders believe their technology will accelerate EV adoption. (Battery costs make up 30 to 40 percent of the price of EVs, according to the Institute for Energy Research).

    “Lithium-ion batteries have made huge improvements over the years, but even Elon Musk says we need some breakthrough technology,” Ota says, referring to the CEO of EV firm Tesla. “To make EVs more common, we need a production cost breakthrough; we can’t just rely on cost reduction through scaling because we already make a lot of batteries today.”

    24M is also working to prove out new battery chemistries that its partners could quickly incorporate into their gigafactories. In January of this year, 24M received a grant from the Department of Energy’s ARPA-E program to develop and scale a high-energy-density battery that uses a lithium metal anode and semi-solid cathode for use in electric aviation.

    That project is one of many around the world designed to validate new lithium-ion battery chemistries that could enable a long-sought battery revolution. As 24M continues to foster the creation of large scale, global production lines, the team believes it is well-positioned to turn lab innovations into ubiquitous, world-changing products.

    “This technology is a platform, and our vision is to be like Google’s Android [operating system], where other people can build things on our platform,” Ota says. “We want to do that but with hardware. That’s why we’re licensing the technology. Our partners can use the same production lines to get the benefits of new chemistries and approaches. This platform gives everyone more options.” More

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    MADMEC winner identifies sustainable greenhouse-cooling materials

    The winners of this year’s MADMEC competition identified a class of materials that could offer a more efficient way to keep greenhouses cool.

    After Covid-19 put the materials science competition on pause for two years, on Tuesday SmartClime, a team made up of three MIT graduate students, took home the first place, $10,000 prize.

    The team showed that a type of material that changes color in response to an electric voltage could reduce energy usage and save money if coated onto the panes of glass in greenhouses.

    “This project came out of our love of gardening,” said SmartClime team member and PhD candidate Isabella Caruso in the winning presentation. “Greenhouses let you grow things year-round, even in New England, but even greenhouse pros need to use heating furnaces in the winter and ventilation in the summer. All of that can be very labor- and energy-intensive.”

    Current options to keep greenhouses cool include traditional air conditioning units, venting and fans, and simple cloth. To develop a better solution, the team looked through scientific papers to find materials with the right climate control properties.

    Two classes of materials that looked promising were thermochromic coatings, which change color based on temperature, and electrochromic solutions, which change color based on electric voltage.

    Creating both the thermochromic and electrochromic solutions required the team to assemble nanoparticles and spin-coat them onto glass substrates. In lab tests, the electrochromic material performed well, turning a deep bluish hue to reduce the heat coming into the greenhouse while also letting in enough light for plants. Specifically, the electrochromic cell kept its test box about 1 to 3 degrees Celsius cooler than the test box coated in regular glass.

    The team estimated that greenhouse owners could make back the added costs of the electrochromic paneling through savings on other climate-control measures. Additional benefits of using the material include reducing heat-related crop losses, increasing crop yields, and reducing water requirements.

    Hosted by MIT’s Department of Materials Science and Engineering (DMSE), the competition was the culmination of team projects that began last spring and included a series of design challenges throughout the summer. Each team received guidance, access to equipment and labs, and up to $1,000 in funding to build and test their prototypes.

    “It’s great to be back and to have everyone here in person,” Mike Tarkanian, a senior lecturer in DMSE and coordinator of MADMEC, said at the event. “I’ve enjoyed getting back to normal, doing the design challenges over the summer and celebrating with everyone here today.”

    The second-place prize was split between YarnZ, which identified a nanofiber yarn that is more sustainable than traditional textile fibers, and WasteAway, which has developed a waste bin monitoring device that can identify the types of items thrown into trash and recycling bins and flag misplaced items.

    YarnZ (which stands for Yarns Are Really NanofiberZ), developed a nanofiber yarn that is more degradable than traditional microfiber yarns without sacrificing on performance.

    A large chunk of the waste and emissions in the clothing industry come from polyester, a slow-degrading polymer that requires an energy-intensive melt spinning process before it’s spun into the fibers of our clothes.

    “The biggest thing I want to impress upon you today is that the textile industry is a major greenhouse gas-producing entity and also produces a huge amount of waste,” YarnZ member and PhD candidate Natalie Mamrol said in the presentation.

    To replace polyester, the team developed a continuous process in which a type of nanofiber film collects in a water bath before being twisted into yarn. In subsequent tests, the nanofiber-based yarn degraded more quicky than traditional microfibers and showed comparable durability. YarnZ believes this early data should encourage others to explore nanofibers as a viable replacement in the clothing industry and to invest in scaling the approach for industrial settings.

    WasteAway’s system includes a camera that sits on top of trash bins and uses artificial intelligence to recognize items that people throw away.

    Of the 300 million tons of waste generated in the U.S. each year, more than half ends up in landfills. A lot of that waste could have been composted or recycled but was misplaced during disposal.

    “When someone throws something into the bin, our sensor detects the motion and captures an image,” explains WasteAway’s Melissa Stok, an undergraduate at MIT. “Those images are then processed by our machine-learning algorithm to find contamination.”

    Each device costs less than $30, and the team says that cost could go down as parts are bought at larger scales. The insights gleaned from the device could help waste management officials identify contaminated trash piles as well as inform education efforts by revealing common mistakes people make.

    Overall, Tarkanian believes the competition was a success not only because of the final results, but because of the experience the students got throughout the MADMEC program, which included several smaller, hands-on competitions involving laser cutters, 3-D printers, soldering irons, and other equipment many students said they had never used before.

    “They end up getting into the lab through these design challenges, which have them compete in various engineering tasks,” Tarkanian says. “It helps them get comfortable designing and prototyping, and they often end up using those tools in their research later.” More

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    New process could enable more efficient plastics recycling

    The accumulation of plastic waste in the oceans, soil, and even in our bodies is one of the major pollution issues of modern times, with over 5 billion tons disposed of so far. Despite major efforts to recycle plastic products, actually making use of that motley mix of materials has remained a challenging issue.

    A key problem is that plastics come in so many different varieties, and chemical processes for breaking them down into a form that can be reused in some way tend to be very specific to each type of plastic. Sorting the hodgepodge of waste material, from soda bottles to detergent jugs to plastic toys, is impractical at large scale. Today, much of the plastic material gathered through recycling programs ends up in landfills anyway. Surely there’s a better way.

    According to new research from MIT and elsewhere, it appears there may indeed be a much better way. A chemical process using a catalyst based on cobalt has been found to be very effective at breaking down a variety of plastics, such as polyethylene (PET) and polypropylene (PP), the two most widely produced forms of plastic, into a single product, propane. Propane can then be used as a fuel for stoves, heaters, and vehicles, or as a feedstock for the production of a wide variety of products — including new plastics, thus potentially providing at least a partial closed-loop recycling system.

    The finding is described today in the open access journal  JACS Au, in a paper by MIT professor of chemical engineering Yuriy Román-Leshkov, postdoc Guido Zichitella, and seven others at MIT, the SLAC National Accelerator Laboratory, and the National Renewable Energy Laboratory.

    Recycling plastics has been a thorny problem, Román-Leshkov explains, because the long-chain molecules in plastics are held together by carbon bonds, which are “very stable and difficult to break apart.” Existing techniques for breaking these bonds tend to produce a random mix of different molecules, which would then require complex refining methods to separate out into usable specific compounds. “The problem is,” he says, “there’s no way to control where in the carbon chain you break the molecule.”

    But to the surprise of the researchers, a catalyst made of a microporous material called a zeolite that contains cobalt nanoparticles can selectively break down various plastic polymer molecules and turn more than 80 percent of them into propane.

    Although zeolites are riddled with tiny pores less than a nanometer wide (corresponding to the width of the polymer chains), a logical assumption had been that there would be little interaction at all between the zeolite and the polymers. Surprisingly, however, the opposite turned out to be the case: Not only do the polymer chains enter the pores, but the synergistic work between cobalt and the acid sites in the zeolite can break the chain at the same point. That cleavage site turned out to correspond to chopping off exactly one propane molecule without generating unwanted methane, leaving the rest of the longer hydrocarbons ready to undergo the process, again and again.

    “Once you have this one compound, propane, you lessen the burden on downstream separations,” Román-Leshkov says. “That’s the essence of why we think this is quite important. We’re not only breaking the bonds, but we’re generating mainly a single product” that can be used for many different products and processes.

    The materials needed for the process, zeolites and cobalt, “are both quite cheap” and widely available, he says, although today most cobalt comes from troubled areas in the Democratic Republic of Congo. Some new production is being developed in Canada, Cuba, and other places. The other material needed for the process is hydrogen, which today is mostly produced from fossil fuels but can easily be made other ways, including electrolysis of water using carbon-free electricity such as solar or wind power.

    The researchers tested their system on a real example of mixed recycled plastic, producing promising results. But more testing will be needed on a greater variety of mixed waste streams to determine how much fouling takes place from various contaminants in the material — such as inks, glues, and labels attached to the plastic containers, or other nonplastic materials that get mixed in with the waste — and how that affects the long-term stability of the process.

    Together with collaborators at NREL, the MIT team is also continuing to study the economics of the system, and analyzing how it can fit into today’s systems for handling plastic and mixed waste streams. “We don’t have all the answers yet,” Román-Leshkov says, but preliminary analysis looks promising.

    The research team included Amani Ebrahim and Simone Bare at the SLAC National Accelerator Laboratory; Jie Zhu, Anna Brenner, Griffin Drake and Julie Rorrer at MIT; and Greg Beckham at the National Renewable Energy Laboratory. The work was supported by the U.S. Department of Energy (DoE), the Swiss National Science Foundation, and the DoE’s Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office (AMO), and Bioenergy Technologies Office (BETO), as part of the the Bio-Optimized Technologies to keep Thermoplastics out of Landfills and the Environment (BOTTLE) Consortium. More

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    3 Questions: Janelle Knox-Hayes on producing renewable energy that communities want

    Wind power accounted for 8 percent of U.S. electricity consumption in 2020, and is growing rapidly in the country’s energy portfolio. But some projects, like the now-defunct Cape Wind proposal for offshore power in Massachusetts, have run aground due to local opposition. Are there ways to avoid this in the future?

    MIT professors Janelle Knox-Hayes and Donald Sadoway think so. In a perspective piece published today in the journal Joule, they and eight other professors call for a new approach to wind-power deployment, one that engages communities in a process of “co-design” and adapts solutions to local needs. That process, they say, could spur additional creativity in renewable energy engineering, while making communities more amenable to existing technologies. In addition to Knox-Hayes and Sadoway, the paper’s co-authors are Michael J. Aziz of Harvard University; Dennice F. Gayme of Johns Hopkins University; Kathryn Johnson of the Colorado School of Mines; Perry Li of the University of Minnesota; Eric Loth of the University of Virginia; Lucy Y. Pao of the University of Colorado; Jessica Smith of the Colorado School of Mines; and Sonya Smith of Howard University.

    Knox-Hayes is the Lister Brothers Associate Professor of Economic Geography and Planning in MIT’s Department of Urban Studies and Planning, and an expert on the social and political context of renewable energy adoption; Sadoway is the John F. Elliott Professor of Materials Chemistry in MIT’s Department of Materials Science and Engineering, and a leading global expert on developing new forms of energy storage. MIT News spoke with Knox-Hayes about the topic.

    Q: What is the core problem you are addressing in this article?

    A: It is problematic to act as if technology can only be engineered in a silo and then delivered to society. To solve problems like climate change, we need to see technology as a socio-technical system, which is integrated from its inception into society. From a design standpoint, that begins with conversations, values assessments, and understanding what communities need.  If we can do that, we will have a much easier time delivering the technology in the end.

    What we have seen in the Northeast, in trying to meet our climate objectives and energy efficiency targets, is that we need a lot of offshore wind, and a lot of projects have stalled because a community was saying “no.” And part of the reason communities refuse projects is because they that they’ve never been properly consulted. What form does the technology take, and how would it operate within a community? That conversation can push the boundaries of engineering.

    Q: The new paper makes the case for a new practice of “co-design” in the field of renewable energy. You call this the “STEP” process, standing for all the socio-technical-political-economic issues that an engineering project might encounter. How would you describe the STEP idea? And to what extent would industry be open to new attempts to design an established technology?

    A: The idea is to bring together all these elements in an interdisciplinary process, and engage stakeholders. The process could start with a series of community forums where we bring everyone together, and do a needs assessment, which is a common practice in planning. We might see that offshore wind energy needs to be considered in tandem with the local fishing industry, or servicing the installations, or providing local workforce training. The STEP process allows us to take a step back, and start with planners, policymakers, and community members on the ground.

    It is also about changing the nature of research and practice and teaching, so that students are not just in classrooms, they are also learning to work with communities. I think formalizing that piece is important. We are starting now to really feel the impacts of climate change, so we have to confront the reality of breaking through political boundaries, even in the United States. That is the only way to make this successful, and that comes back to how can technology be co-designed.

    At MIT, innovation is the spirit of the endeavor, and that is why MIT has so many industry partners engaged in initiatives like MITEI [the MIT Energy Initiative] and the Climate Consortium. The value of the partnership is that MIT pushes the boundaries of what is possible. It is the idea that we can advance and we can do something incredible, we can innovate the future. What we are suggesting with this work is that innovation isn’t something that happens exclusively in a laboratory, but something that is very much built in partnership with communities and other stakeholders.

    Q: How much does this approach also apply to solar power, as the other leading type of renewable energy? It seems like communities also wrestle with where to locate solar arrays, or how to compensate homeowners, communities, and other solar hosts for the power they generate.

    A: I would not say solar has the same set of challenges, but rather that renewable technologies face similar challenges. With solar, there are also questions of access and siting. Another big challenge is to create financing models that provide value and opportunity at different scales. For example, is solar viable for tenants in multi-family units who want to engage with clean energy? This is a similar question for micro-wind opportunities for buildings. With offshore wind, a restriction is that if it is within sightlines, it might be problematic. But there are exciting technologies that have enabled deep wind, or the establishment of floating turbines up to 50 kilometers offshore. Storage solutions such as hydro-pneumatic energy storage, gravity energy storage or buoyancy storage can help maintain the transmission rate while reducing the number of transmission lines needed.

    In a lot of communities, the reality of renewables is that if you can generate your own energy, you can establish a level of security and resilience that feeds other benefits. 

    Nevertheless, as demonstrated in the Cape Wind case, technology [may be rejected] unless a community is involved from the beginning. Community involvement also creates other opportunities. Suppose, for example, that high school students are working as interns on renewable energy projects with engineers at great universities from the region. This provides a point of access for families and allows them to take pride in the systems they create.  It gives a further sense of purpose to the technology system, and vests the community in the system’s success. It is the difference between, “It was delivered to me,” and “I built it.” For researchers the article is a reminder that engineering and design are more successful if they are inclusive. Engineering and design processes are also meant to be accessible and fun. More

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    Passive cooling system could benefit off-grid locations

    As the world gets warmer, the use of power-hungry air conditioning systems is projected to increase significantly, putting a strain on existing power grids and bypassing many locations with little or no reliable electric power. Now, an innovative system developed at MIT offers a way to use passive cooling to preserve food crops and supplement conventional air conditioners in buildings, with no need for power and only a small need for water.

    The system, which combines radiative cooling, evaporative cooling, and thermal insulation in a slim package that could resemble existing solar panels, can provide up to about 19 degrees Fahrenheit (9.3 degrees Celsius) of cooling from the ambient temperature, enough to permit safe food storage for about 40 percent longer under very humid conditions. It could triple the safe storage time under dryer conditions.

    The findings are reported today in the journal Cell Reports Physical Science, in a paper by MIT postdoc Zhengmao Lu, Arny Leroy PhD ’21, professors Jeffrey Grossman and Evelyn Wang, and two others. While more research is needed in order to bring down the cost of one key component of the system, the researchers say that eventually such a system could play a significant role in meeting the cooling needs of many parts of the world where a lack of electricity or water limits the use of conventional cooling systems.

    The system cleverly combines previous standalone cooling designs that each provide limited amounts of cooling power, in order to produce significantly more cooling overall — enough to help reduce food losses from spoilage in parts of the world that are already suffering from limited food supplies. In recognition of that potential, the research team has been partly supported by MIT’s Abdul Latif Jameel Water and Food Systems Lab.

    “This technology combines some of the good features of previous technologies such as evaporative cooling and radiative cooling,” Lu says. By using this combination, he says, “we show that you can achieve significant food life extension, even in areas where you have high humidity,” which limits the capabilities of conventional evaporative or radiative cooling systems.

    In places that do have existing air conditioning systems in buildings, the new system could be used to significantly reduce the load on these systems by sending cool water to the hottest part of the system, the condenser. “By lowering the condenser temperature, you can effectively increase the air conditioner efficiency, so that way you can potentially save energy,” Lu says.

    Other groups have also been pursuing passive cooling technologies, he says, but “by combining those features in a synergistic way, we are now able to achieve high cooling performance, even in high-humidity areas where previous technology generally cannot perform well.”

    The system consists of three layers of material, which together provide cooling as water and heat pass through the device. In practice, the device could resemble a conventional solar panel, but instead of putting out electricity, it would directly provide cooling, for example by acting as the roof of a food storage container. Or, it could be used to send chilled water through pipes to cool parts of an existing air conditioning system and improve its efficiency. The only maintenance required is adding water for the evaporation, but the consumption is so low that this need only be done about once every four days in the hottest, driest areas, and only once a month in wetter areas.

    The top layer is an aerogel, a material consisting mostly of air enclosed in the cavities of a sponge-like structure made of polyethylene. The material is highly insulating but freely allows both water vapor and infrared radiation to pass through. The evaporation of water (rising up from the layer below) provides some of the cooling power, while the infrared radiation, taking advantage of the extreme transparency of Earth’s atmosphere at those wavelengths, radiates some of the heat straight up through the air and into space — unlike air conditioners, which spew hot air into the immediate surrounding environment.

    Below the aerogel is a layer of hydrogel — another sponge-like material, but one whose pore spaces filled with water rather than air. It’s similar to material currently used commercially for products such as cooling pads or wound dressings. This provides the water source for evaporative cooling, as water vapor forms at its surface and the vapor passes up right through the aerogel layer and out to the environment.

    Below that, a mirror-like layer reflects any incoming sunlight that has reached it, sending it back up through the device rather than letting it heat up the materials and thus reducing their thermal load. And the top layer of aerogel, being a good insulator, is also highly solar-reflecting, limiting the amount of solar heating of the device, even under strong direct sunlight.

    “The novelty here is really just bringing together the radiative cooling feature, the evaporative cooling feature, and also the thermal insulation feature all together in one architecture,” Lu explains. The system was tested, using a small version, just 4 inches across, on the rooftop of a building at MIT, proving its effectiveness even during suboptimal weather conditions, Lu says, and achieving 9.3 C of cooling (18.7 F).

    “The challenge previously was that evaporative materials often do not deal with solar absorption well,” Lu says. “With these other materials, usually when they’re under the sun, they get heated, so they are unable to get to high cooling power at the ambient temperature.”

    The aerogel material’s properties are a key to the system’s overall efficiency, but that material at present is expensive to produce, as it requires special equipment for critical point drying (CPD) to remove solvents slowly from the delicate porous structure without damaging it. The key characteristic that needs to be controlled to provide the desired characteristics is the size of the pores in the aerogel, which is made by mixing the polyethylene material with solvents, allowing it to set like a bowl of Jell-O, and then getting the solvents out of it. The research team is currently exploring ways of either making this drying process more inexpensive, such as by using freeze-drying, or finding alternative materials that can provide the same insulating function at lower cost, such as membranes separated by an air gap.

    While the other materials used in the system are readily available and relatively inexpensive, Lu says, “the aerogel is the only material that’s a product from the lab that requires further development in terms of mass production.” And it’s impossible to predict how long that development might take before this system can be made practical for widespread use, he says.

    The research team included Lenan Zhang of MIT’s Department of Mechanical Engineering and Jatin Patil of the Department of Materials Science and Engineering. More