Symposium X—Frontiers of Materials Research

Shirley Meng, The University of Chicago

From Atom to System—Tera-Scale Energy Transition with Better Batteries

Written by Alison Hatt

In the final Symposium X talk of the in-person meeting, Shirley Meng, from The University of Chicago, took the audience through a brief history of lithium-ion batteries and shared several stories from her own research career. Throughout her talk, Meng touched on themes of team science and the power of materials scientists to help solve global problems.

At the heart of Meng’s talk was a vision of a future where batteries are not disposable but instead are assets to be recycled and reused. She envisioned each home having a battery supplying “green electrons” from renewable sources, akin to a major appliance like a refrigerator. Batteries of the future must last for decades, she said, and be completely recyclable. We must be responsible for how batteries are produced and how they will continue on planet Earth.

Meng provided a brief history of batteries that stretched back 270 years to when Benjamin Franklin first coined the term “battery,” and included the appearance of the first commercially available lithium-ion batteries in 1992. Lithium-ion batteries have come a long way in the past 30 years, tripling in energy density and gaining a ten-fold increase in lifecycle while also becoming ten times cheaper. Meng underscored the role of materials science enabling every necessary breakthrough along the way, as researchers developed new cathode, anode, and electrolyte materials.

Meng described the lithium ion/metal battery as a complex “living” system and demonstrated the massive volume changes they undergo as they cycle. She emphasized the need for engineering solutions for batteries that are robust to dramatic volume changes, can go through thousands of cycles, and operate reliably in extreme conditions, for applications like aviation.

Meng discussed the value of using atomic-scale information to design better batteries. Among the stories she shared from her own research was work done as a graduate student exploring lithium-rich layered oxides using density functional theory. In the simulations, she found that putting lithium in the transition metal layer pushed oxygen p-levels closer to the Fermi level, allowing the oxygen anion to participate in conduction.

Since that early work, Meng has gone on to tackle countless other questions in the field, a few of which she highlighted today, such as her recent work using cryo-electron microscopy to determine the atomic-level nanostructure of inactive lithium in lithium metal batteries. Intimate knowledge of the lithium metal anode morphology is needed to make these devices maximally efficient and effective, and Meng showed how each study she discussed nudged the field forward, building insight and overcoming obstacles.

As she looked forward to the next decade of energy storage and battery technology, Meng talked about the importance of safety. Even today’s low rates of lithium-ion batteries catching fire would be unacceptable for an in-home appliance-style battery. Solid-state batteries are promising in that regard, and Meng even talked about letting visitors to her lab cut up a solid-state battery with a pair of scissors as a demonstration of their stability (a demonstration not to be repeated at home).

Despite the many exciting research stories Meng shared, she closed by saying that her proudest achievement is the more than fifty students she has mentored. They are the real product of her work, she said. To move the field of battery technology forward, every researcher has a role to play, coming up with creative ideas as well as cranking through the “boring” or less glamorous work that needs to be done. For her, she’s particularly interested right now in partnering with industry, moving ideas from the lab to the marketplace and helping build a healthy ecosystem for battery development.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X—Frontiers of Materials Research

Aditya D. Mohite, Rice University

The Rise of 2D Halide Perovskites

Written by Rahul Rao

When you think of the materials that make solar cells, chances are that you’re thinking of silicon. But silicon has challengers: a class of materials known as halide perovskites, which have achieved gains in efficiency in the last decade that took silicon some thirty years. Still, they have some way to go before they can match silicon's impressive durability.

At Wednesday’s Symposium X, titled “The Rise of 2D Halide Perovskites,” Aditya Mohite of Rice University spoke about his group’s recent work with one avenue of trying to boost that hardiness. His approach: making perovskites that are, as the title suggests, flattened in a two-dimensional plane.

It's a subject with which Mohite is intimately familiar. In 2016, while he was at Los Alamos National Laboratory, Mohite and his colleagues showed that 2D perovskites endured better than their 3D counterparts, even under trying conditions of relatively high humidity and constant light exposure. Mohite says it was a landmark achievement that let flat perovskites shine in a then-3D-dominated field. But to build them into practical solar cells, researchers needed to zoom in on several challenges.

One issue arises from the beginning. Making 2D halide perovskites might mean dissolving a crystalline powder in a solution, then depositing it on a surface, letting it form a film. Impurities often seep in during that process. As a result, even if you have a powder with properties you desire, they might vary in the final film, and the same impurities can drag down the solar cell’s efficiency. 

So, Mohite and his colleagues developed a new, phase-selective method of depositing perovskites. They found that this new method reduced many of the impurities, and drastically improved both the durability and efficiency of the material.

After you make the 2D material, its properties might change under light — a rather crucial consideration for a material that’s meant to be out in the Sun for the entirety of its lifetime. Mohite and his colleagues studied these effects by taking their perovskites to a synchrotron beamline. Most notably, they found that the material seemed to contract in the light. If they put the material back in the dark, the effect reversed.

It turned out that the culprits were iodine atoms, situated in the perovskites’ structure such that they faced each other. If those atoms were placed closer, the material experienced more contraction. In fact, Mohite and his colleagues found an unexpected boon: contraction made it easier for electrical charge to traverse the material, boosting its conductivity and, again, its efficiency.

Two-dimensional perovskites don’t need to be separate from their 3D counterparts; indeed, they seem to work best together. Mohite’s group has explored taking, for instance, a sheet of glass, stacking a layer of 3D perovskite atop it, then topping it all with a 2D film. 

Through exploring such stacks, Mohite’s group has found the best stability yet. One such system could continue operating for hundreds and thousands of hours, even in the raw heat and humidity of Rice University’s Houston climate. If progress like this can continue, Mohite said, then halide perovskites — which can already compete with silicon’s efficiency — may soon approach its durability, too.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X—Frontiers of Materials Research

Donhee Ham, Harvard University
Brain, Copy and Paste
Written by Sophia Chen

Neurons in the brain function by transmitting electric signals, which is why researchers use electronics to study them. In addition, computing researchers are also looking to the brain for inspiration to design new types of computers, known as neuromorphic computers. At Tuesday’s Symposium X, Donhee Ham of Harvard University discussed his research in connecting biological neurons to semiconductor electronics in a talk titled, “Brain, Copy and Paste.”

Ham’s group has been working on a technology that can record multiple neurons’ electric activity in parallel from within the cells themselves. One goal is to use these electric signals to create a network map of neuron activity.

Ham contrasted his work with existing technology known as the “patch clamp electrode” first developed in the 1970s. These electrodes can pick up excellent signal-to-noise ratio, as they take measurements within the cells themselves. However, the electrodes can only measure one neuron at a time. Ham also compared his group’s technology to microelectrode arrays such as those by the companies Neurolink and Neuropixel. These arrays pick up signals from multiple neurons in parallel but they deliver more noise because they do not measure directly from inside the cell.

Ham’s research team is developing a CMOS nanoelectrode array. Over the last 11 years, they have made four generations of these chips, with the fifth generation underway. Ham’s presentation focused on the second-generation chip. He shared some lessons they learned along the way. For example, they determined that they could not measure neural activity by applying a voltage, because they ended up measuring that applied voltage rather than the neuron signals themselves.

The array consisted of 4,096 pixels array arranged in a 64 by 64 grid. They were able to measure more than 300 synaptic connections from 1700 neurons with a 20-minute recording.

In their newest iteration, the chip can measure about 3500 sites. Ham said that his group is moving toward applying the arrays to in vivo research, as cultured cells do not have the same geometry as naturally occurring biological networks.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X—Frontiers of Materials Research

Jennifer Dionne, Stanford University

The Light Stuff: Enabling Sustainable, Product-Selective Photocatalysts with Plasmonics

Written by Sophia Chen

From the synthesis of fertilizer to the production of plastics, the chemical manufacturing industry is built on energy-intense processes. During Monday’s Symposium X, Jennifer Dionne of Stanford University discussed a method of designing catalysts using atomic-scale resolution to make chemical manufacturing more sustainable.

Many chemical manufacturing processes require reactions at high temperatures, as Dionne described in her talk, titled “The Light Stuff: Enabling Sustainable, Product-Selective Photocatalysts with Plasmonics.” Manufacturers reach the high temperatures through the burning of fossil fuels. To lower the heat needed for these reactions, Dionne and her team research photocatalysts, which accelerate chemical reactions when triggered with light.

Photocatalysts include metal nanoparticles, such as platinum, palladium, or silver. Dionne presented a study on the use of such nanoparticles as photocatalysts in a hydrogenation reaction. Light creates hotspots on the nanoparticles to catalyze chemical reactions. These hotspots form due to the generation of plasmons, which are collective oscillations of the material’s electrons. They study the nanoparticles under these conditions using a technique called optically-coupled transmission electron microscopy.

The goal is to use plasmons as a “chemical scalpel” to design the catalysts at an atomic scale, said Dionne. By controlling when and where the plasmons form, they can orchestrate more energy-efficient chemical reactions.

Plasmons on a nanoparticle can also enable the catalyst in new chemical reactions. Because the plasmons create nonequilibrium conditions in the nanoparticle, they can “open up entirely new reaction pathways,” said Dionne. “We're not just expediting reactions, but we're also enabling new transformations,” she said.

Looking ahead, Dionne pointed out two fields of necessary research. They need to develop the microscopic theory of how plasmons work in these materials. In addition, they need to better link imaging of these photocatalysts to reactor performance.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X—Frontiers of Materials Research

Naomi J. Halas, Rice University

Nanomaterials and Light Addressing Global Challenges

Written by Don Monroe

In her Symposium X presentation, Naomi J. Halas of Rice University highlighted two promising projects using light-nanomaterial interactions to address major global problems: access to clean water and energy consumption in chemical production.

The first project, “Transformative Enhancements in Solar Desalination,” involves water purification. Worldwide, “one billion people do not have access to clean water,” Halas said.

One technique, known as membrane distillation, essentially evaporates heated water on one side of a membrane and condenses it on the other side. Unfortunately, the energy required to heat and vaporize water is prohibitive.

Halas described a scheme to use solar illumination to vaporize the water, by adding light-absorbing nanoparticles, such as gold nanoshells or carbon black. Interestingly, she said, “most of the energy goes into steam generation, not heating.” High concentrations of added particles repeatedly scatter the light near the surface, until they finally absorb it.

One challenge is that the heat of vaporization and condensation opposes the heat gradient across the membrane. To counteract this effect, Halas and her research team added a heat exchanger. Under certain conditions, she said, the combination acts as a resonator, increasing the amount of purified water produced by as much as 500%. “When you get into the right resonant regime you can store energy in this coupled system,” Halas said, and it can be retained even when clouds are passing by.

In her second topic, “Plasmonic Photocatalysis,” Halas addressed the enormous energy usage of the chemical industry. Much of this energy goes to heat to drive reactions, she said. “We need to figure out ways to do chemistry with less energy.”

Nanoparticles can provide a route to driving reactions more directly through hot electrons and holes generated from plasmons excited by light. If appropriate energy levels are available, these hot carriers can efficiently stimulate chemical reactions even before the carriers thermalize as general heating. “It wasn’t until localized surface plasmons came along that this became accessible,” Halas noted.

One challenge is that the best plasmonic metals, Cu, Ag, and Au, are great light harvesters but weak catalysts. Platinum-group metals, such as Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt are excellent catalysts but poor plasmonic materials.

Halas and her colleagues realized that they could decorate a plasmonic nanoparticle, often Al, with catalytic metals. The nanoparticle acts as an antenna that transfers absorbed light energy to the catalysts. “We can do plasmon-induced chemistry right on the surface of the particle,” Halas said.

Halas described how reactions can be accelerated, such as with the addition of hydrogen to acetylene. The photo-catalyzed process shows 40 times better selectivity for the desired ethylene product over ethane.

Another opportunity is the generation of hydrogen from ammonia, which could easily be stored and used for hydrogen generation on demand. Experiments show that the hot electrons accelerated the rate-limiting desorption step. “We’re changing the reaction pathway altogether,” Halas said.

One potentially profound application is the reforming of methane, in which CH₄ and CO₂—the two dominant greenhouse gases—are turned into CO and H₂, a combination known as syngas. Using a small amount of Ru in Cu, the photocatalytically assisted process can proceed at temperatures hundreds of degrees lower than a thermal process, much more selectively and with record energy efficiency.

Commercialization of this technology is being pursued by a company, Syzygy, that Halas helped launch. Their reactors use light from light-emitting diodes, hopefully powered by renewable energy, to drive the photocatalytic process. Halas noted that since 2018 they have scaled up methane-reforming technology by a factor of 500,000, to kilograms per day.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X — Frontiers of Materials Research

Pupa Gilbert, University of Wisconsin-Madison and Lawrence Berkeley National Laboratory

Diverse But Convergent Mesostructure in Biominerals

Written by Sophia Chen

During Wednesday’s Symposium X, Pupa Gilbert encouraged the audience to contribute to the field of biominerals—the study of biologically-produced, hard structures ranging from teeth and bones to eggshells and mother-of pearl.

“It doesn’t matter if you’re a mathematician or a physicist or material scientist,” the University of Wisconsin-Madison physicist said. “[…]If you [use] a skill you already have on a biomineral, you will make big, fundamental, important discoveries.”

Biominerals are distinct among materials as their functions have been optimized via evolution. Nature has “already debugged” the design, said Gilbert. As biominerals make up much of the fossil record, they also provide clues about the evolution of life on Earth. Broadly, an organism’s biominerals must offer some evolutionary edge, as that organism had to expend energy to produce it, she said.

Researchers have only investigated a handful of biominerals, said Gilbert. “The few organisms that we have studied have revealed an immense wealth of information and fundamental discoveries,” she said.

Gilbert’s talk focused on biominerals made of calcium carbonate (CaCO₃). These biominerals come in three different crystalline structures known as calcite, aragonite, and vaterite. Sea urchin spines are made from calcite, and Gilbert showed examples of corals made of aragonite and vaterite.

She shared studies of nacre, the iridescent material also known as mother-of-pearl, which is made of aragonite. To study the organisms, Gilbert developed a technique known as polarization-dependent imaging contrast (PIC) mapping. The method allows Gilbert to measure the orientation of the crystals in her samples.  

Curiously, three different classes of marine organism—bivalve, cephalopod, and gastropod—all independently evolved the capability to produce nacre. The nacre’s surface for all three organism types resembles a mosaic of irregular polygons. The recurrence of these similar structures indicates that nacre confers an advantage to these organisms, such as protecting them from predators, said Gilbert.

The organisms also undergo similar processes to produce nacre. For one, the organisms all form the nacre from amorphous nanoparticles. Gilbert hypothesizes that this process is optimized for faster crystal growth. The nacre crystals also grow in slightly misoriented directions with respect to their neighboring crystals. Gilbert hypothesizes that the misorientation toughens the nacre and presented a few studies supporting that idea. In atom-level simulations, for example, her team demonstrated that misoriented crystals deflect cracks, preventing catastrophic damage to the nacre’s structure.

Gilbert says that they would like to know more about how the organisms grow the structures, such as how a mollusk is able to orient nacre crystals to maximize the biomineral’s toughness. Perhaps the materials science community could draw inspiration from these biological processes to develop more eco-friendly materials synthesis processes, she said.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X — Frontiers of Materials Research

M. Stanley Whittingham, Binghamton University

The Lithium Battery: From a Dream to Readiness to Take-On Climate Change—The Materials Challenges

Written by Prachi Patel

Lithium-ion batteries are going to be essential in the fight against climate change by allowing the electrification of transport and providing large-scale storage for renewable energy, M. Stanley Whittingham said in his Symposium X talk. The lithium-ion battery pioneer and 2019 Nobel Prize laureate outlined the materials challenges that battery developers need to tackle to harness the full potential of lithium-ion batteries.

Intercalation-based lithium battery chemistry, which involves inserting lithium ions into layered electrode materials, has undergone many different incarnations since Whittingham created the first cell in 1972 at an Exxon research laboratory, based on a titanium disulfide cathode and a lithium–aluminum anode.

Researchers have developed many different electrode materials over the years. The anode today is typically made of graphite. “The Holy Grail now is to try and go back to a lithium metal anode,” he says.

Cathode materials, meanwhile, are usually lithium cobalt oxide, iron phosphate, and the lithium nickel manganese cobalt oxides (NMC) and lithium nickel cobalt aluminum oxides (NCA) widely used in EV batteries. However, the energy density of these materials is only up to 26% of theoretical capacity. “The key thing to note is that there’s huge opportunity for improvement,” he said, calling for young materials researchers to find better cathode materials.

Whittingham is part of the Battery 500 Consortium, a team of researchers from national laboratories, universities, and industry who aim to create batteries with an energy density of 500 Wh/kg, more than double that of current batteries.

To boost energy density, the Consortium researchers have increased nickel content in the NMC materials to 60 percent. In June, the team reported a battery made with this NMC622 cathode and a lithium metal anode that had an energy density over 350 Wh/kg and that could be charged 600 times. The Consortium is pushing for even higher lifetime and density while keeping costs down.

One challenge with this chemistry is that the large volume of ions going in and out of the NMC622 particles—which have a meatball morphology made of several crystals clumped into spheres—can crack the particles. Another issue is that after the first charging cycle, not all the lithium ions extracted from the cathode can be re-inserted. Whittingham and his colleagues recently found that a lithium niobium oxide coating on the NMC622 particles eliminates half of this first-cycle loss by reducing surface impurities and impedance.

Using single-crystal NMC622 particles less than 3µm in size, instead of the meatball morphology, could address the cracking problem. The lower surface area means less side reactions, translating to much longer lifetimes, Whittingham explained. So the Consortium is trying to find the best single-crystal morphology to replace the meatball-like NMC622 particles.

Another cathode material that might deserve a second look are phosphates, he said. Lithium iron phosphate is a promising material that is low-cost, stable, and safe, and has no first-cycle loss. But it suffers from low density. He and his colleagues are also testing lithium vanadium phosphate as a possible high-density cathode material candidate. Cuboid particles of the material can take up two lithium ions instead of one during the intercalation process without damaging the crystal lattice.

Whittingham concluded his talk by presenting other challenges that need to be solved for a greener lithium-ion battery ecosystem. That includes safe and stable electrolytes; new manufacturing and recycling technologies; clean mining; and regional supply chains.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

John M. Martinis, Frontiers of Materials Research

MRS TV talks with John M. Martinis of the University of California, Santa Barbara about his 2021 MRS Fall Meeting Symposium X talk on Materials for Superconducting Qubits.

 

 

Symposium X: Frontiers of Materials Research

John M. Martinis, University of California, Santa Barbara
Materials for Superconducting Qubits

Written by Sophia Chen

During Monday’s Symposium X, titled “Materials for Superconducting Qubits,” John M. Martinis explained that materials scientists have an important role to play in the development of quantum computing.

Martinis, the former head of Google’s quantum computing hardware team, said that one key challenge is to make better quality qubits, the fundamental building blocks of a quantum computer. Like a classical bit, a qubit can represent a 1 or a 0—but it can also be a superposition of both values, or become entangled with another qubit. In theory, this enables complex and precise computations such as modeling drug molecules or batteries that are inaccessible to classical computers.

However, existing quantum computers make too many mistakes to execute useful algorithms. These errors may arise, for example, from the qubit’s inability to stay in the same physical state—and thus preserve information—for a long period of time. That’s why quantum researchers are working to develop more robust qubits. “Understanding how to design materials is a big part of that,” said Martinis, now CEO of Quantala and a physics professor at the University of California, Santa Barbara.

Martinis discussed specific materials issues with superconducting qubits, which consist of micron-scale superconducting circuits built on millimeter-scale silicon chips similar to conventional computing chips. Google and IBM, for example, have built their quantum machines using superconducting qubits. These qubits exhibit quantum effects, such as currents that can move in a superposition of two different directions. These effects enable the parallel computations that are a hallmark of quantum computation.

Researchers need to reduce loss from each qubit to improve its information retention. The qubits consist of superconducting electrodes on silicon substrate with oxide layers forming at each material interface. A major source of loss comes from qubit materials’ surfaces, particularly at interfaces of different materials on the chip, said Martinis. Quantum researchers have found that electrodes made of niobium or tantalum have less loss than aluminum-based electrodes, and the conventional wisdom attributes the better performance to materials reasons.

However, Martinis thinks it is still unclear why niobium and tantalum have made better qubits. Researchers have not thoroughly investigated the geometry dependence on qubit quality. For example, users of niobium and tantalum have not reported how size affects their qubit’s loss. He invited materials scientists to tackle these fundamental questions, which would help researchers improve predictive modeling while designing a quantum computer.

In 2019, Martinis led a team at Google to build a 54-qubit quantum computer to perform a task in a few minutes that they claimed would take a supercomputer 10,000 years. Since then, other researchers claimed to develop a classical algorithm that beats the quantum computer at that task. Still, Martinis’s achievement ignited momentum among quantum researchers of the promise of quantum computing. Experts have yet to conclusively show whether a quantum computer can perform useful tasks beyond what a classical computer can achieve.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X: Frontiers of Materials Research

Iuliana P. Radu, imec
How New and Old Materials Research and Know-How Extend the Increase in Computation Power

Written by Sophia Chen

Iuliana Radu of the Interuniversity Microelectronics Centre (imec), an institute dedicated to the research and development of nanoelectronics in Belgium, delivered a Symposium X lecture on Friday. Radu, a physicist by training, discussed how materials science can further increase computational power.

We currently live in an era where “the data center is the programming unit,” said Radu. People no longer store most of their data locally, instead piping it to a data center and processing it offsite. This has motivated the need for more powerful computation.

At imec, Radu and her colleagues develop the next generation of computers, where one approach is to shrink the transistor further. While researchers are studying a variety of materials and strategies for this, Radu’s presentation focused on a class of materials known as transition metal dichalcogenides. As a two-dimensional material—in other words, when the material occurs as a single atomic layer—transition metal dichalcogenides can make transistors smaller by shortening its so-called gate length, compared to when they are made from silicon.  One example of such a material is tungsten disulfide, which Radu has studied.

Radu described the current research on integrating these materials in transistors. One challenge is depositing them in stacked nanosheets on a substrate in a scalable process. Researchers are also studying the defects that occur in these materials.

In addition, researchers are considering how materials science can benefit future quantum computers. Radu anticipates this new type of computer, based not on transistors but on components known as quantum bits, or qubits, to be a paradigm shift for the field of computation, as they are capable of performing very different algorithms than classical computers.

Radu discussed two materials for making qubits—semiconductors and superconductors. Both types of qubit function at low temperatures near absolute zero, and the classical electronics that control the qubit will require materials that can function at these low temperatures.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.