Researchers devise a practical solution for preventing corrosive CRUD buildup in nuclear systems.
When clogs and corrosion threaten residential water and heating systems, homeowners can simply call a plumber to snake a drain or replace a pipe. Operators of nuclear power plants aren’t nearly so lucky. Metallic oxide particles, collectively known as CRUD in the nuclear energy world, build up directly on reactor fuel rods, impeding the plant’s ability to generate heat. These foulants cost the nuclear energy industry millions of dollars annually.
This issue has vexed the nuclear energy industry since its start in the 1960s, and scientists have only found ways to mitigate, but not cure, CRUD buildup. But that may be about to change. “We believe we have cracked the problem of CRUD,” says Michael Short, Class of ’42 Associate Professor of Nuclear Science and Engineering (NSE), and research lead. “Every test we’ve done so far has looked good.”
In a recent paper published online by Langmuir, an American Chemical Society journal, Short and MIT colleagues describe their work, which offers a novel approach to designing fouling-resistant materials for use in nuclear reactors and other large-scale energy systems. Co-authors on the paper are Cigdem Toparli, a postdoc in NSE at the time of the study; NSE graduate students Max Carlson and Minh A. Dinh; and Bilge Yildiz, professor of nuclear science and engineering and of materials science and engineering.
The team’s research goes beyond theory and lays out specific design principles for anti-foulant materials. “One important aspect of our project was to make a practical solution to the problem today — no pie-in-the-sky for our children’s generation, but something that has to work with everything that exists now,” says Short.
Exelon, one of the nation’s largest power generators, is confident enough in the viability of the MIT team’s anti-foulant designs that it has started making plans to validate them in one of its commercial reactors. In the highly regulated domain of nuclear energy, the time from research idea to application could set a speed record.
The forces behind CRUD
Short has been investigating CRUD since 2010, when he joined the Consortium for Advanced Simulation of Light Water Reactors (CASL), a project sponsored by the U.S. Department of Energy to improve the performance of current and future nuclear reactors. As a postdoc at MIT, he developed computer models of CRUD.
“This made me read a lot about CRUD, and how different surface forces can cause things to stick to each other, such as the corrosion products circulating in coolant fluid that accumulate on fuel rods,” says Short. “I wanted to learn how it accumulates in the first place, and maybe find a way to actually prevent CRUD formation.”
Toward that end, he set up a boiling chamber made out of spare parts in the basement of Building NW22 to see which materials stuck to each other, and received a small grant to learn how to test the growth of CRUD in reactor conditions in Japan. He and his students built a flow loop (a way of recreating reactor conditions without radiation), and conducted a series of experiments to see which materials encouraged, and which discouraged, the growth of CRUD.
Researchers have floated a host of surface forces as candidates for causing the stickiness behind CRUD: hydrogen bonding, magnetism, electrostatic charges. But through experimentation and computational analysis, Short and his team began to suspect an overlooked contender: van der Waals forces. Discovered by 19th-century Dutch physicist Johannes Diderik van der Waals, these are weak electric forces that account for some of the attraction of molecules to each other in liquid, solids, and gases.
“We could rule out other surface forces for simple reasons, but one force we couldn’t rule out was van der Waals,” says Short.
Then came a major breakthrough: Carlson recalled a 50-year-old equation developed by Russian physicist Evgeny Lifshitz that he had come across during a review of materials science literature.
“Lifshitz’s theory described the magnitude of van der Waals forces according to electron vibrations, where electrons in different materials vibrate at different frequencies and at different amplitudes, such as the stuff floating in coolant water, and fuel rod materials,” describes Short. “His math tells us if the solid materials have the same electronic vibrations as water, nothing will stick to them.”
This, says Short, was the team’s “Aha” moment. If cladding, the outer layer of fuel rods, could be coated with a material that matched the electronic frequency spectrum of coolant water, then these particles would slip right past the fuel rod. “The answer was sitting in the literature for 50 years, but nobody recognized it in this way,” says Short.
“This was real thinking outside the box,” says Chris Stanek, a technical director at Los Alamos National Laboratory engaged in nuclear energy advanced modeling and simulation, who was not involved in the research. “It was an unconventional, MIT approach — to step back and look at the source of fouling, to find something no one else had in the literature, and then getting straight to the physical underpinnings of CRUD.”
One design principle
The researchers got to work demonstrating that van der Waals was the single most important surface force behind the stickiness of CRUD. In search of a simple and uniform way of calculating materials’ molecular frequencies, they seized on the refractive light index — a measure of the amount light bends as it passes through a material. Shining calibrated LED light on material samples, they created a map of the optical properties of nuclear fuel and cladding materials. This enabled them to rate materials on a stickiness scale. Materials sharing the same optical properties, according to the Lifshitz theory, would prove slippery to each other, while those far apart on the refractive light scale would stick together.
Researchers have devised a practical solution for preventing corrosive buildup in nuclear systems. Image shows specimens of a standard reactor zirconium alloy with and without our CRUD-resistant coating. The uncoated specimens at left are covered with CRUD in our flowing reactor experiment, while the two coated specimens came out as clean as they went in.
Image: Mike Short/Department of Nuclear Science and Engineering
By the end of their studies, as the paper describes, Short’s team had not only come up with a design principle for anti-foulant materials but a group of candidate coatings whose optical properties made them a good (slippery) match for coolant fluids. But in actual experiments, some of their coatings didn’t work. “It wasn’t enough to get the refractive index right,” says Short. “Materials need to be hard, resistant to radiation, hydrogen, and corrosion, and capable of being fabricated at large scale.”
Additional trials, including time in the harsh environment of MIT’s Nuclear Reactor Laboratory, have yielded a few coating materials that meet most of these tough criteria. The final step is determining if these materials can stop CRUD from growing in a real reactor. It is a test with a start date expected next year, at an Exelon commercial nuclear plant.
“Fuel rods coated with antifoulant materials will go into an operating commercial reactor putting power on the grid,” says Short. “At different intervals, they come out for examination, and if all goes right, our rods are clean and the ones next door are dirty,” says Short. “We could be one long test away from stopping CRUD in this type of reactor, and if we eliminate CRUD, we’ve wiped away a scourge of the industry.”
Funders of this research include Exelon Corporation through the MIT Energy Initiative’s Center for Advanced Nuclear Energy Systems; Statoil Petroleum AS (now Equinor); and the International Collaborative Energy Technology R&D Program of the Korea Institute of Energy Technology Evaluation and Planning, which is funded by the Korean Ministry of Trade Industry and Energy.
Leda Zimmerman | Department of Nuclear Science and Engineering
Read more from MIT News
Abstract: The theme of this year’s meeting will largely be focused on imaging-enabled nanoscale research on the structure, properties and processing of materials. Invited speakers will describe new tools and methods for atomic-scale structural and chemical characterization of materials, and application of these methods to optimization of processing and properties of materials for a wide range of applications. Results from imaging-based in situ studies of vapor- and liquid-phase processes for synthesis of nanostructured materials and in situ studies of nano- and micro-scale phenomena that can be used to engineer properties of bulk materials will be presented. Development of compact high-brilliance X-ray sources that can provide synchrotron-level materials analyses with laboratory-scale systems will also be discussed. Studies of nanoscale electronic, photonic, mechanical and catalytic properties of materials will be included and discussion of prospects for development of new state-of-the-art tools and methods for imaging-based and x–ray based materials research will be featured.
We are no longer accepting registrations but you are welcome to register in person on the day of the event. Lunch will only be provided to people who pre-registered.
A new framework calculates companies’ beneficial environmental "handprints" as well as their negative footprints, to encourage eco-friendly actions.
Gregory Norris is an expert on quantifying firms’ impacts on the environment over the life cycles of their products and processes. His analyses help decision-makers opt for more sustainable, Earth-friendly outputs.
Painted handprints and inspirational quotes greeted participants in a workshop about humans' impacts on the environment, both positive (handprints) and negative (footprints). The workshop featured a talk by MIT’s Gregory Norris.
Photo: Jenna Cramer
He and others in this field of life-cycle assessment (LCA) have largely gone about their work by determining firms’ negative impacts on the environment, or footprints, a term most people are familiar with. But Norris felt something was missing. What about the positive impacts firms can have by, for example, changing behaviors or creating greener manufacturing processes that become available to competitors? Could they be added to the overall LCA tally?
Introducing handprints, the term Norris coined for those positive impacts and the focus of MIT’s Sustainability and Health Initiative for NetPositive Enterprise (SHINE). SHINE is co-led by Norris and Randolph Kirchain, who both have appointments through MIT’s Materials Research Laboratory (MRL).
“If you ask LCA practitioners what they track to determine a product’s sustainability, 99 out of 100 will talk about footprints, these negative impacts,” Norris says. “We’re about expanding that to include handprints, or positive impacts.”
Says Kirchain, “we’re trying to make the [LCA] metrics more encompassing so firms are motivated to make positive changes as well.” And that could ultimately “increase the scope of activities that firms engage in for environmental benefits.”
In a February 2021 paper in the International Journal of Life Cycle Assessment, Norris, Kirchain, and colleagues lay out the methodology for not only estimating handprints but also combining them with footprints. Additional authors of the paper are Jasmina Burek, Elizabeth A. Moore, and Jeremy Gregory, who are also affiliated with the MRL.
“By giving handprints a defendable methodology, we get closer to the ideal place where everything that counts can be counted,” says Jeff Zeman, principal of TrueNorth Collective, a consulting firm for sustainability. Zeman was not involved in the work.
As a result, Zeman continues, “designers can see the positive impact of their work show up in an organization’s messaging, as progress toward its sustainability goals, and bridge their work with other good actors to create shared benefits. Handprints have been a powerful influence on me and my team — and continue to be.”
How it works
Handprints are measured with the same metrics used for quantifying different footprints. For example, a classic metric for determining a product’s water footprint is the liters of water used to create that product. The same product’s water handprint would be calculated by determining the liters of water saved through a positive change such as instituting a new manufacturing process involving recycled materials. Both footprints and handprints are measured using existing life-cycle inventory databases, software, and calculation methods.
The SHINE team has demonstrated the impact of adding handprints to LCA analyses through case studies with several companies. One such study described in the paper involved Interface, a manufacturer of flooring materials. The SHINE team calculated the company’s handprints associated with the use of “recycled” gas to help heat its manufacturing facility. Specifically, Interface captured and burned methane gas from a landfill. That gas would otherwise have been released to the atmosphere, contributing to climate change.
After calculating both the company’s handprints and footprints, the SHINE team found that Interface had a net positive impact. As the team wrote in their paper, “with the SHINE handprint framework, we can help actors to create handprints greater than, and commensurate with, their footprints.”
Concludes Norris: “With this paper, we hope that work on sustainability will get stronger by making these tools available to more people.”
Elizabeth A. Thomson | Materials Research Laboratory
Publication Date: March 29, 2021
The external advisory board dinner will be held on October 9, 2019. Immediately following the Materials Day Poster Session.
Location: MIT Student Center, West Lounge
Cocktails will start at 6:30pm.
The advisory board meeting will be held on October 10, 2019.
Location: Bush Room, Building 10-105
8:30am - 4:30pm
Machine Learning in Materials Research
MATERIALS DAY AGENDA
October 9, 2019
MIT, Kresge Theatre (W16)
Kresge Lobby, MIT Bldg. W16
||Welcome and Overview
Professor Carl V. Thompson
Director, Materials Research Laboratory, MIT
Accelerating Materials Design and Discovery for Electric Vehicles
Dr. Brian Storey
Director, Accelerated Materials Design & Discovery, TOYOTA Research Institute
||Text and Data Mining for Material Synthesis
Associate Professor Elsa Olivetti
Department of Materials Science & Engineering, MIT
Advancing Chemical Development Through Process Intensification, Automation, and Machine Learning
|11:00-12:00pm||Poster Previews: 2-minute talks by selected poster presenters|
Stratton Student Center, 3rd Floor
Twenty Chimneys/Mezzanine Lounge (Building W20)
|Computing at MIT
Professor Asu Ozdaglar
Department Head, Electrical Engineering & Computer Science, MIT
||Machine Learning in Optics: From Spectrum Reconstruction to Metasurface Design
Associate Professor Juejun (JJ) Hu
Department of Materials Science & Engineering, MIT
||Elastic Strain Engineering for Unprecedented Properties
Professor Ju Li
Departments of Nuclear Science & Eng. and Materials Science & Engineering, MIT
Learning matter: Materials Design Through Atomistic Simulations and Machine Learning
||Session Wrap Up
Professor Carl V. Thompson
Director, Materials Research Laboratory, MIT
||Poster Session and Social
La Sala de Puerto Rico, 2nd Floor
Stratton Student Center (Building W20)
Headed by Carl Thompson, the newly formed Materials Research Laboratory opens up opportunities for industrial partnerships.
Inside a high-performance integrated circuit, the copper wiring is tens of nanometers in diameter, with a coating that is a few nanometers thick. “If you took all this wiring and connected it and stretched it out, it would be about 20 kilometers long,” says Carl Thompson, professor of materials science and engineering. “And it all has to work, and it has to work for years.”
That’s just one sample, from his own work, of the challenges MIT’s enormous spectrum of materials research – ranging from quantum devices all the way to buildings and roads. “There’s one researcher in metallurgy who makes objects that weigh a ton, in the same laboratory where people make objects that weigh nanograms,” Thompson notes.
Formed in 2017 by combining two longstanding MIT centers, the Materials Research Laboratory [MRL] acts as an umbrella for this work. About 70 faculty are directly involved in the MRL. The total materials research community at MIT includes about 150 faculty, from all departments in the School of Engineering and many in the School of Science.
Materials research spans many disciplines, and projects often bring together researchers with very different sets of expertise, Thompson says. He emphasizes that the MRL’s strengthened ability to foster and accelerate such interdisciplinary work will boost partnerships with industry, where interdisciplinary collaborations are a norm.
Incentives for collaborations
Corporate connections have been central to Thompson’s own research, which focuses primarily on making thin films, micromaterials, and nanomaterials and integrating them into microelectronic and microelectromechanical devices.
“I’ve found that I can have impact on real systems that people can buy only by being deeply involved with industry,” Thompson says. “Industry partnerships have informed not only my research but my teaching, because I can talk about why some of the more fundamental problems in materials science and engineering are very important in applications that we all depend on.”
“It’s incredibly important for students and postdocs to interact with industry, and to understand the real problems and the real constraints,” he adds. “Many things sound great in the laboratory, and many of them are great, and eventually will become part of devices and systems. But there are many steps in between, and it’s very important for everybody in an academic community to understand that.”
Thompson’s research also underlines the necessity for cross-discipline collaborations – for instance, in his current research on thin-film batteries.
“There are projections that by 2025 there will be hundreds of billions of sensors out there in the Internet of Things, and we can't do that if we have to change the batteries on all of those all the time,” he remarks. “If you can make them with batteries and an energy source, then they can be autonomous, so you don't need to ever change the battery.”
His group seeks not only to develop thin film battery materials but to integrate these materials with other components such as circuits, sensors and microelectromechanical devices.
“There’s a relationship between how you make the materials, what their structure is, and the performance of not only the material in the device but also the device itself,” Thompson says. “That work is very highly collaborative with people in other disciplines, such as electrical engineering and mechanical engineering. Materials research is critical; chemistry and physics are critical. So is understanding the factors that lead to the failure of batteries, and a mathematician here at MIT in collaboration with engineers and physical scientists has made a very important contribution to that topic.”
“In batteries, a small interdisciplinary working group has blossomed into an area of great expertise that is very highly interactive with industry,” he says. “Now the MRL is ideally positioned to help make collaborations like this happen.”
Photo, David Sella.
Merging into the MRL
The MRL combines MIT’s long-established Materials Processing Center [which was funded by industry, government agencies, and foundations] with the Center for Materials Science and Engineering [which performed basic science with experimental facilities supported by the National Science Foundation]. Geoffrey Beach, associate professor of materials science and engineering, is MRL co-director.
“One of the main reasons we did the merger was so that we could do all these complementary activities together,” Thompson says. “Academics tend to work in silos, and you want to take people out of them to see how what they do is relevant to applications that other people do. MIT is very good about that. But the MRL, which takes the two communities together, will be an even better place to make those matches.”
Importantly, the MRL is also tightly joined to the new MIT.nano facility, a 200,000-square-foot center for nanoscience and nanotechnology scheduled to open this summer, designed as a global powerhouse for research expertise and equipment. MRL researchers will be able to leverage the newly assembled MIT.nano resources that are unique within academia, Thompson says.
Even more broadly, Thompson and his colleagues are using MIT’s convening power to provide leadership outside the Institute as well. One set of efforts will be workshops in industrial sectors such as aerospace and microelectronics, which will bring companies, academics, and often government agencies to discuss research opportunities and current development challenges.
Other projects will build consortia designed to create a sustained mechanism for companies to collaborate to support pre-competitive research that benefits them all. For example, one existing consortium studies the use of carbon nanotubes to create stronger and lighter aircraft fuselage materials.
On a larger scale, MRL can sponsor meetings with industry, academia, and government to address global challenges, such as sustainable materials processing and supply of critical materials. “For instance, cobalt is mined primarily in the Congo, which is not a good situation on many levels, but are there alternatives?” Thompson says. “And how can you make material with lower energy costs, not only in making the material but over the period of its use? How do you make it in a way that doesn't affect the environment? And how do you recycle the materials?”
“There's been a real renaissance in looking at these questions, at the same times in the same laboratories where people are doing fundamental innovations at the atomic scale.,” Thompson says. “That's one of the exciting aspects of materials research.”
– Eric Bender, MIT ILP
June 5, 2018
Chemistry World featured an article Oct. 10, 2017, on Associate Professor of Metallurgy Antoine Allanore’s work to produce potassium fertilizer from potassium feldspar using an efficient hydrothermal process.
The scientific paper by by research scientist Davide Ciceri, visiting engineer Marcelo de Oliveira and Allanore, in Green Chemistry is free to access until November 20, 2017.
Study finds the wettability of porous electrode surfaces is key to making efficient water-splitting or carbon-capturing systems.
Using electricity to split water into hydrogen and oxygen can be an effective way to produce clean-burning hydrogen fuel, with further benefits if that electricity is generated from renewable energy sources. But as water-splitting technologies improve, often using porous electrode materials to provide greater surface areas for electrochemical reactions, their efficiency is often limited by the formation of bubbles that can block or clog the reactive surfaces.
This image shows the interplay among electrode wettability, porous structure, and overpotential. With the decrease of wettability (moving left to right), the gas-evolving electrode transitions from an internal growth and departure mode to a gas-filled mode, associated with a drastic change of bubble behaviors and significant increase of overpotential.
Courtesy of the researchers
Now, a study at MIT has for the first time analyzed and quantified how bubbles form on these porous electrodes. The researchers have found that there are three different ways bubbles can form on and depart from the surface, and that these can be precisely controlled by adjusting the composition and surface treatment of the electrodes.
The findings could apply to a variety of other electrochemical reactions as well, including those used for the conversion of carbon dioxide captured from power plant emissions or air to form fuel or chemical feedstocks. The work is described today in the journal Joule, in a paper by MIT visiting scholar Ryuichi Iwata, graduate student Lenan Zhang, professors Evelyn Wang and Betar Gallant, and three others.
“Water-splitting is basically a way to generate hydrogen out of electricity, and it can be used for mitigating the fluctuations of the energy supply from renewable sources,” says Iwata, the paper’s lead author. That application was what motivated the team to study the limitations on that process and how they could be controlled.
Because the reaction constantly produces gas within a liquid medium, the gas forms bubbles that can temporarily block the active electrode surface. “Control of the bubbles is a key to realizing a high system performance,” Iwata says. But little study had been done on the kinds of porous electrodes that are increasingly being studied for use in such systems.
The team identified three different ways that bubbles can form and release from the surface. In one, dubbed internal growth and departure, the bubbles are tiny relative to the size of the pores in the electrode. In that case, bubbles float away freely and the surface remains relatively clear, promoting the reaction process.
In another regime, the bubbles are larger than the pores, so they tend to get stuck and clog the openings, significantly curtailing the reaction. And in a third, intermediate regime, called wicking, the bubbles are of medium size and are still partly blocked, but manage to seep out through capillary action.
The team found that the crucial variable in determining which of these regimes takes place is the wettability of the porous surface. This quality, which determines whether water spreads out evenly across the surface or beads up into droplets, can be controlled by adjusting the coating applied to the surface. The team used a polymer called PTFE, and the more of it they sputtered onto the electrode surface, the more hydrophobic it became. It also became more resistant to blockage by larger bubbles.
New experiments showed that the wettability of the surface makes a big difference in the way bubbles form and leave the surface. On the left, a higher-wettability porous surface leads to small bubbles that leave quickly, while lower wettability, right, leads to bigger bubbles that clog the material's pores and reduce efficiency.
The transition is quite abrupt, Zhang says, so even a small change in wettability, brought about by a small change in the surface coating’s coverage, can dramatically alter the system’s performance. Through this finding, he says, “we’ve added a new design parameter, which is the ratio of the bubble departure diameter [the size it reaches before separating from the surface] and the pore size. This is a new indicator for the effectiveness of a porous electrode.”
Pore size can be controlled through the way the porous electrodes are made, and the wettability can be controlled precisely through the added coating. So, “by manipulating these two effects, in the future we can precisely control these design parameters to ensure that the porous medium is operated under the optimal conditions,” Zhang says. This will provide materials designers with a set of parameters to help guide their selection of chemical compounds, manufacturing methods and surface treatments or coatings in order to provide the best performance for a specific application.
While the group’s experiments focused on the water-splitting process, the results should be applicable to virtually any gas-evolving electrochemical reaction, the team says, including reactions used to electrochemically convert captured carbon dioxide, for example from power plant emissions.
Gallant, an associate professor of mechanical engineering at MIT, says that “what’s really exciting is that as the technology of water splitting continues to develop, the field’s focus is expanding beyond designing catalyst materials to engineering mass transport, to the point where this technology is poised to be able to scale.” While it’s still not at the mass-market commercializable stage, she says, “they’re getting there. And now that we’re starting to really push the limits of gas evolution rates with good catalysts, we can’t ignore the bubbles that are being evolved anymore, which is a good sign.”
The MIT team also included Kyle Wilke, Shuai Gong, and Mingfu He. The work was supported by Toyota Central R&D Labs, the Singapore-MIT Alliance for Research and Technology (SMART), the U.S.-Egypt Science and Technology Joint Fund, and the Natural Science Foundation of China.
David L. Chandler | MIT News Office
Publication Date: March 26, 2021
Use of a novel electrolyte could allow advanced metal electrodes and higher voltages, boosting capacity and cycle life.
Lithium-ion batteries have made possible the lightweight electronic devices whose portability we now take for granted, as well as the rapid expansion of electric vehicle production. But researchers around the world are continuing to push limits to achieve ever-greater energy densities — the amount of energy that can be stored in a given mass of material — in order to improve the performance of existing devices and potentially enable new applications such as long-range drones and robots.
X-ray tomography images taken at Brookhaven National Lab show cracking of a particle in one electrode of a battery cell that used a conventional electrolyte (as seen on the left). The researchers found that using a novel electrolyte prevented most of this cracking (right).
Image: courtesy of the researchers
One promising approach is the use of metal electrodes in place of the conventional graphite, with a higher charging voltage in the cathode. Those efforts have been hampered, however, by a variety of unwanted chemical reactions that take place with the electrolyte that separates the electrodes. Now, a team of researchers at MIT and elsewhere has found a novel electrolyte that overcomes these problems and could enable a significant leap in the power-per-weight of next-generation batteries, without sacrificing the cycle life.
The research is reported today in the journal Nature Energy in a paper by MIT professors Ju Li, Yang Shao-Horn, and Jeremiah Johnson; postdoc Weijiang Xue; and 19 others at MIT, two national laboratories, and elsewhere. The researchers say the finding could make it possible for lithium-ion batteries, which now typically can store about 260 watt-hours per kilogram, to store about 420 watt-hours per kilogram. That would translate into longer ranges for electric cars and longer-lasting changes on portable devices.
The basic raw materials for this electrolyte are inexpensive (though one of the intermediate compounds is still costly because it’s in limited use), and the process to make it is simple. So, this advance could be implemented relatively quickly, the researchers say.
The electrolyte itself is not new, explains Johnson, a professor of chemistry. It was developed a few years ago by some members of this research team, but for a different application. It was part of an effort to develop lithium-air batteries, which are seen as the ultimate long-term solution for maximizing battery energy density. But there are many obstacles still facing the development of such batteries, and that technology may still be years away. In the meantime, applying that electrolyte to lithium-ion batteries with metal electrodes turns out to be something that can be achieved much more quickly.
The new application of this electrode material was found “somewhat serendipitously,” after it had initially been developed a few years ago by Shao-Horn, Johnson, and others, in a collaborative venture aimed at lithium-air battery development.
“There’s still really nothing that allows a good rechargeable lithium-air battery,” Johnson says. However, “we designed these organic molecules that we hoped might confer stability, compared to the existing liquid electrolytes that are used.” They developed three different sulfonamide-based formulations, which they found were quite resistant to oxidation and other degradation effects. Then, working with Li’s group, postdoc Xue decided to try this material with more standard cathodes instead.
The type of battery electrode they have now used with this electrolyte, a nickel oxide containing some cobalt and manganese, “is the workhorse of today’s electric vehicle industry,” says Li, who is a professor of nuclear science and engineering and materials science and engineering.
Because the electrode material expands and contracts anisotropically as it gets charged and discharged, this can lead to cracking and a breakdown in performance when used with conventional electrolytes. But in experiments in collaboration with Brookhaven National Laboratory, the researchers found that using the new electrolyte drastically reduced these stress-corrosion cracking degradations.
The problem was that the metal atoms in the alloy tended to dissolve into the liquid electrolyte, losing mass and leading to cracking of the metal. By contrast, the new electrolyte is extremely resistant to such dissolution. Looking at the data from the Brookhaven tests, Li says, it was “sort of shocking to see that, if you just change the electrolyte, then all these cracks are gone.” They found that the morphology of the electrolyte material is much more robust, and the transition metals “just don’t have as much solubility” in these new electrolytes.
That was a surprising combination, he says, because the material still readily allows lithium ions to pass through — the essential mechanism by which batteries get charged and discharged — while blocking the other cations, known as transition metals, from entering. The accumulation of unwanted compounds on the electrode surface after many charging-discharging cycles was reduced more than tenfold compared to the standard electrolyte.
“The electrolyte is chemically resistant against oxidation of high-energy nickel-rich materials, preventing particle fracture and stabilizing the positive electrode during cycling,” says Shao-Horn, a professor of mechanical engineering and materials science and engineering. “The electrolyte also enables stable and reversible stripping and plating of lithium metal, an important step toward enabling rechargeable lithium-metal batteries with energy two times that of the state-the-art lithium-ion batteries. This finding will catalyze further electrolyte search and designs of liquid electrolytes for lithium-metal batteries rivaling those with solid state electrolytes.”
The next step is to scale the production to make it affordable. “We make it in one very easy reaction from readily available commercial starting materials,” Johnson says. Right now, the precursor compound used to synthesize the electrolyte is expensive, but he says, “I think if we can show the world that this is a great electrolyte for consumer electronics, the motivation to further scale up will help to drive the price down.”
Because this is essentially a “drop in” replacement for an existing electrolyte and doesn’t require redesign of the entire battery system, Li says, it could be implemented quickly and could be commercialized within a couple of years. “There’s no expensive elements, it’s just carbon and fluorine. So it’s not limited by resources, it’s just the process,” he says.
David L. Chandler | MIT News Office
Publication Date: March 25, 2021
Summer Scholar Stephanie Bauman interns in Luqiao Liu lab synthesizing and testing manganese gallium samples for spintronic applications.
Assistant Professor of Electrical Engineering Luqiao Liu is developing new magnetic materials known as antiferromagnets, such as manganese gallium samples, that can be operated at room temperature by reversing their electron spin and can serve as the basis for long lasting, spintronic computer memory. Materials Processing Center – Center for Materials Science and Engineering [MPC-CMSE] Summer Scholar Stephanie Bauman spent her internship making and testing these new materials.
Bauman, a University of South Florida physics major, says, “In our project we're working on the area of spintronics, anti-ferromagnetic devices that switch electron spin controlled by a current. I'm working with a lot of new equipment like the vibrating sample magnetometer and the sputterer to lay down thin films.”
“I’ve been working on a daily basis with Joe Finley, who is a graduate student here, and he’s been a explaining a lot of things to me,” Bauman notes. “It’s a very dense subject matter. And he does help me out a lot when we go to things like the X-ray diffraction room, and he shows me how the graphs can interpret how thick each layer of the thin layers of the devices are. He’s really helpful and easy to work with.”
During a visit to the lab, where she synthesizes these thin films with a special machine called a sputter deposition chamber, Bauman says, “I always go back to the checklist just to make sure I'm doing everything in the right order.” In order to take out a sample from the machine she has to follow a complicated set of steps, making sure its parts are correctly lined up and unhooking the sample holder in the main chamber. Because the chamber is pressurized, she must bring it back to everyday atmospheric pressure before taking it out. “Now that I can see that it disengaged, I go ahead and move it all the way back up,” she says. With the sample holder on a moveable arm, she can rotate it out.
|2017 MPC-CMSE Summer Scholar Stephanie Bauman holds a sample of manganese gallium, a new material known as an antiferromagnet, that can serve as the basis for long lasting, spintronic computer memory devices operated by reversing electron spin at room temperature. She interned this summer in the lab of Assistant Professor of Electrical Engineering Luqiao Liu. Photo, Denis Paiste, Materials Processing Center.|
The sample moves across a gear arm out of the main chamber into transfer chamber known as a load lock. “A very, very important part of this is to make sure you close the transfer valve again, otherwise you mess up the pressure in the main chamber,” she says. After double-checking the transfer valve is closed, she brings the load lock back to sea level pressure of 760 Torr. Then she takes out the sample holder.
“As you can see the sample is really tiny. It's half a centimeter by a half a centimeter, which is what we're working with right now,” Bauman says. As she loosens the screws on the arms holding the sample in place, she notes that she has to be careful not to scratch the sample with the arms. Once safely removed, she places the sample in a special holder labeled based on when each sample was made, which sample of the day it is and its thickness. That way, she notes, “we can refer back to that in our data so that we know what thickness levels that we’re testing.”
“Sometimes you end up playing tiddlywinks. I know that some younger people don't really know what that game is, but it's what it looks like when you push down on the arm, and the sample goes flying,” Bauman cautions.
Bauman then demonstrates how a new sample is loaded into the sputterer device. “Carefully tighten the screw, making sure not to torque it too much, then you move the other arm into place,” she says. Once both arms are tightened on the sample holder, she can put the sample into the load lock. “Very simple just make sure it's lined up correctly. It's also important to make sure the O-ring is clean, and so is the lid before you put it back on. That way there's a very good seal. So that's really it for the loading, and then you just turn the vacuum pumps back on and wait until it reaches the appropriate pressure and then load it into the main chamber.”
“I'm actually a non-traditional student, which means I'm a little bit older,” Bauman explains. “I have been in the military for 20 years, and I also had a civilian career for a long time in aviation contracts. I decided to go back to school for physics, and it's really been rewarding, especially this internship.”
Bauman’s internship is supported in part by NSF’s Materials Research Science and Engineering Centers program [grant DMR-14-19807]. Participants in the Research Experience for Undergraduates, co-sponsored by the Materials Processing Center and the Center for Materials Science and Engineering, presented their results at a poster session during the last week of the program. The program ran from June 15, 2017, to August 5, 2017, on the MIT campus in Cambridge, Mass.
– Denis Paiste, Materials Processing Center
Sept. 25, 2017
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|2017 MPC-CMSE Summer Scholar Stephanie Bauman presents her poster on her internship in the lab of Assistant Professor of Electrical Engineering Luqiao Liu making and testing new materials known as antiferromagnets, such as manganese gallium, that can serve as the basis for long lasting, spintronic computer memory devices operated by reversing their electron spin at room temperature. Photo, Denis Paiste, Materials Processing Center.|