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Sodium-ion batteries are a valid alternative to Lithium-ion batteries

Lithium (Li)-ion batteries (LIBs) are the electrochemical energy storage systems of choice for a wide variety of applications, however other types of emerging battery technologies are currently on the path to share their dominant position.

Among them Sodium (Na)-ion batteries (NIBs) have great potential to represent the next generation low cost and environmentally friendly energy storage solution. The diverse key performance indicators required by different applications and the market diversification is the driving force pushing the Na-ion technology closer to the market.

A team of scientists including WMG at the University of Warwick combined their knowledge and expertise to assess the current status of the Na-ion technology from materials to cell development, offering a realistic comparison of the key performance indicators for NBs and LIBs.

LIBs play a primary role in the transition to a low carbon economy. However, as the market rapidly expands, the environmental and social challenges associated with the mass production of LIBs is triggering large attention toward the search for alternative energy storage solutions based on materials that can be sourced in a sustainable and responsible way. In this scenario, NIBs represent an alternative low cost, sustainable and more environmentally friendly energy storage technology.

In the paper ‘Challenges of today for Na-based batteries of the future: from materials to cell metrics’, published on the 18th of September 2020 in the Journal of Power Sources, a large team of Na-ion technology expert scientists, led by WMG, at the University of Warwick (UK) analyse the prospect of NIBs taking a spot in the energy storage market. The paper also includes researchers from: Helmholtz Institute Ulm (Germany), College de France (France), Humboldt University Berlin (Germany), Institute for Energy technology (Norway), Universit√© de Picardie Jules Verne (France), University of Bordeaux (France) and CIC energiGUNE (Spain).

Na- based batteries offer a combination of attractive properties. They are low cost, use sustainable precursors and have secure raw material supplies. In addition, they are considered as a drop-in technology which could benefit from the already existing Li-ion batteries manufacturing facilities.

As Li-based systems, Na-based batteries come in different forms, such as Na-ion, Na-all-solid-state-batteries, NaO2 and Na/S. While the last ones are seen as disruptive future technologies, the Na-ion technology represent an attractive technology almost ready to challenge the Li-ion batteries in specific applications.

Performance metrics are of utmost importance for the SIB technology to ensure a competitive cost per Wh and find a place in the market. In this work, the most promising electrode materials and electrolyte systems have been reviewed and performance metrics from the academic literature have been used to extrapolate full sodium ion cells performance indicators.

Authors indicate that with the ongoing development, the present best materials available for Na-ion cells should allow approaching the energy density of the present generation of Li-ion commercial cells. One of the most important application field for the developed sodium-ion battery prototypes is certainly stationary energy storage systems, where cost and cycle life represent two fundamental parameters. “In this field sodium-ion batteries have the potential to dominate the future market representing the most promising system to fill the gap between energy production and utilization by securing energy supply. However high-power applications in the electrified automotive field are a potential niche field application for NIBs” says Dr Ivana Hasa, Assistant Professor at WMG.

Further technological improvements are needed to increase the performance especially in terms of energy density. Extremely encouraging results have been achieved for the Na-ion technology in a very short time when compared to the Li-ion technology. Technological improvement will be achieved by cell component fabrication/assembly optimization, as occurred in the last thirty years for the LIB technology.

Dr Ivana Hasa, from WMG, University of Warwick comments: “From an applied research point of view, the future research efforts should be devoted on fundamental research, materials discovery and understanding of the thermodynamic and kinetic processes governing the chemistry of these systems. In addition, the investigation of upscaled Na-ion batteries is of primary importance to obtain realistic data to benchmark the progress of the technology as well as the adoption of a common reporting methodology in the scientific community enabling a fair comparison among performance results.”

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Fast calculation dials in better batteries

A simpler and more efficient way to predict performance will lead to better batteries, according to Rice University engineers.

That their method is 100,000 times faster than current modeling techniques is a nice bonus.

The analytical model developed by materials scientist Ming Tang and graduate student Fan Wang of Rice University’s Brown School of Engineering doesn’t require complex numerical simulation to guide the selection and design of battery components and how they interact.

The simplified model developed at Rice — freely accessible online — does the heavy lifting with an accuracy within 10% of more computationally intensive algorithms. Tang said it will allow researchers to quickly evaluate the rate capability of batteries that power the planet.

The results appear in the open-access journal Cell Reports Physical Science.

There was a clear need for the updated model, Tang said.

“Almost everyone who designs and optimizes battery cells uses a well-established approach called P2D (for pseudo-two dimensional) simulations, which are expensive to run,” Tang said. “This especially becomes a problem if you want to optimize battery cells, because they have many variables and parameters that need to be carefully tuned to maximize the performance.

“What motivated this work is our realization that we need a faster, more transparent tool to accelerate the design process, and offer simple, clear insights that are not always easy to obtain from numerical simulations,” he said.

Battery optimization generally involves what the paper calls a “perpetual trade-off” between energy (the amount it can store) and power density (the rate of its release), all of which depends on the materials, their configurations and such internal structures as porosity.

“There are quite a few adjustable parameters associated with the structure that you need to optimize,” Tang said. “Typically, you need to make tens of thousands of calculations and sometimes more to search the parameter space and find the best combination. It’s not impossible, but it takes a really long time.”

He said the Rice model could be easily implemented in such common software as MATLAB and Excel, and even on calculators.

To test the model, the researchers let it search for the optimal porosity and thickness of an electrode in common full- and half-cell batteries. In the process, they discovered that electrodes with “uniform reaction” behavior such as nickel-manganese-cobalt and nickel-cobalt-aluminum oxide are best for applications that require thick electrodes to increase the energy density.

They also found that battery half-cells (with only one electrode) have inherently better rate capability, meaning their performance is not a reliable indicator of how electrodes will perform in the full cells used in commercial batteries.

The study is related to the Tang lab’s attempts at understanding and optimizing the relationship between microstructure and performance of battery electrodes, the topic of several recent papers that showed how defects in cathodes can speed lithium absorption and how lithium cells can be pushed too far in the quest for speed.

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Predicting the slow death of lithium-ion batteries

Batteries fade as they age, slowly losing power and storage capacity.

As in people, aging plays out differently from one battery to another, and it’s next to impossible to measure or model all of the interacting mechanisms that contribute to decline. As a result, most of the systems used to manage charge levels wisely and to estimate driving range in electric cars are nearly blind to changes in the battery’s internal workings.

Instead, they operate more like a doctor prescribing treatment without knowing the state of a patient’s heart and lungs, and the particular ways that environment, lifestyle, stress and luck have ravaged or spared them. If you’ve kept a laptop or phone for enough years, you may have seen where this leads firsthand: Estimates of remaining battery life tend to diverge further from reality over time.

Now, a model developed by scientists at Stanford University offers a way to predict the true condition of a rechargeable battery in real-time. The new algorithm combines sensor data with computer modeling of the physical processes that degrade lithium-ion battery cells to predict the battery’s remaining storage capacity and charge level.

“We have exploited electrochemical parameters that have never been used before for estimation purposes,” said Simona Onori, assistant professor of energy resources engineering in Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). The research appears Sept. 11 in the journal IEEE Transactions on Control Systems Technology.

The new approach could help pave the way for smaller battery packs and greater driving range in electric vehicles. Automakers today build in spare capacity in anticipation of some unknown amount of fading, which adds extra cost and materials, including some that are scarce or toxic. Better estimates of a battery’s actual capacity will enable a smaller buffer.

“With our model, it’s still important to be careful about how we are using the battery system,” Onori explained. “But if you have more certainty around how much energy your battery can hold throughout its entire lifecycle, then you can use more of that capacity. Our system reveals where the edges are, so batteries can be operated with more precision.”

The accuracy of the predictions in this model — within 2 percent of actual battery life as gathered from experiments, according to the paper — could also make it easier and cheaper to put old electric car batteries to work storing energy for the power grid. “As it is now, batteries retired from electric cars will vary widely in their quality and performance,” Onori said. “There has been no reliable and efficient method to standardize, test or certify them in a way that makes them competitive with new batteries custom-built for stationary storage.”

Dropping old assumptions

Every battery has two electrodes — the cathode and the anode — sandwiching an electrolyte, usually a liquid. In a rechargeable lithium-ion battery, lithium ions shuttle back and forth between the electrodes during charging and discharging. An electric car may run on hundreds or thousands of these small battery cells, assembled into a big battery pack that typically accounts for about 30 percent of the total vehicle cost.

Traditional battery management systems typically rely on models that assume the amount of lithium in each electrode never changes, said lead study author Anirudh Allam, a PhD student in energy resources engineering. “In reality, however, lithium is lost to side reactions as the battery degrades,” he said, “so these assumptions result in inaccurate models.”

Onori and Allam designed their system with continuously updated estimates of lithium concentrations and a dedicated algorithm for each electrode, which adjusts based on sensor measurements as the system operates. They validated their algorithm in realistic scenarios using standard industry hardware.

On the road

The model relies on data from sensors found in the battery management systems running in electric cars on the road today. “Our algorithm can be integrated into current technologies to make them operate in a smarter fashion,” Onori said. In theory, many cars already on the road could have the algorithm installed on their electronic control units, she said, but the expense of that kind of upgrade makes it more likely that automakers would consider the algorithm for vehicles not yet in production.

The team focused their experiments on a type of lithium-ion battery commonly used in electric vehicles (lithium nickel manganese cobalt oxide) to estimate key internal variables such as lithium concentration and cell capacity. But the framework is general enough that it should be applicable to other kinds of lithium-ion batteries and to account for other mechanisms of battery degradation.

“We showed that our algorithm is not just a nice theoretical work that can run on a computer,” she said. “Rather, it is a practical, implementable algorithm which, if adopted and used in cars tomorrow, can result in the ability to have longer-lasting batteries, more reliable vehicles and smaller battery packs.”

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New anode material could lead to safer fast-charging batteries

Scientists at UC San Diego have discovered a new anode material that enables lithium-ion batteries to be safely recharged within minutes for thousands of cycles. Known as a disordered rocksalt, the new anode is made up of earth-abundant lithium, vanadium and oxygen atoms arranged in a similar way as ordinary kitchen table salt, but randomly. It is promising for commercial applications where both high energy density and high power are desired, such as electric cars, vacuum cleaners or drills.

The study, jointly led by nanoengineers in the labs of Professors Ping Liu and Shyue Ping Ong, was published in Nature on September 2.

Currently, two materials are used as anodes in most commercially available lithium-ion batteries that power items like cell phones, laptops and electric vehicles. The most common, a graphite anode, is extremely energy dense — a lithium ion battery with a graphite anode can power a car for hundreds of miles without needing to be recharged. However, recharging a graphite anode too quickly can result in fire and explosions due to a process called lithium metal plating. A safer alternative, the lithium titanate anode, can be recharged rapidly but results in a significant decrease in energy density, which means the battery needs to be recharged more frequently.

This new disordered rocksalt anode — Li3V2O5 — sits in an important middle ground: it is safer to use than graphite, yet offers a battery with at least 71% more energy than lithium titanate.

“The capacity and energy will be a little bit lower than graphite, but it’s faster, safer and has a longer life. It has a much lower voltage and therefore much improved energy density over current commercialized fast charging lithium-titanate anodes,” said Haodong Liu, a postdoctoral scholar in Professor Ping Liu’s lab and first author of the paper. “So with this material we can make fast-charging, safe batteries with a long life, without sacrificing too much energy density.”

The researchers formed a company called Tyfast in order to commercialize this discovery. The startup’s first markets will be electric buses and power tools, since the characteristics of the Li3V2O5 disordered rocksalt make it ideal for use in devices where recharging can be easily scheduled.

Researchers in Professor Liu’s lab plan to continue developing this lithium-vanadium oxide anode material, while also optimizing other battery components to develop a commercially viable full cell.

“For a long time, the battery community has been looking for an anode material operating at a potential just above graphite to enable safe, fast charging lithium-ion batteries. This material fills an important knowledge and application gap,” said Ping Liu. “We are excited for its commercial potential since the material can be a drop-in solution for today’s lithium-ion battery manufacturing process.”

Why try this material?

Researchers first experimented with disordered rocksalt as a battery cathode six years ago. Since then, much work has been done to turn the material into an efficient cathode. Haodong Liu said the UC San Diego team decided to test the material as an anode based on a hunch.

“When people use it as a cathode they have to discharge the material to 1.5 volts,” he said. “But when we looked at the structure of the cathode material at 1.5 volts, we thought this material has a special structure that may be able to host more lithium ions — that means it can go to even lower voltage to work as an anode.”

In the study, the team found that their disordered rocksalt anode could reversibly cycle two lithium ions at an average voltage of 0.6 V — higher than the 0.1 V of graphite, eliminating lithium metal plating at a high charge rate which makes the battery safer, but lower than the 1.5 V at which lithium-titanate intercalates lithium, and therefore storing much more energy.

The researchers showed that the Li3V2O5 anode can be cycled for over 6,000 cycles with negligible capacity decay, and can charge and discharge energy rapidly, delivering over 40 percent of its capacity in 20 seconds. The low voltage and high rate of energy transfer are due to a unique redistributive lithium intercalation mechanism with low energy barriers.

Postdoctoral scholar Zhuoying Zhu, from Professor Shyue Ping Ong’s Materials Virtual Lab, performed theoretical calculations to understand why the disordered rocksalt Li3V2O5 anode works as well as it does.

“We discovered that Li3V2O5 operates via a charging mechanism that is different from other electrode materials. The lithium ions rearrange themselves in a way that results in both low voltage as well as fast lithium diffusion,” said Zhuoying Zhu.

“We believe there are other electrode materials waiting to be discovered that operate on a similar mechanism,” added Ong.

The experimental studies at UC San Diego were funded by awards from the UC San Diego startup fund to Ping Liu, while the theoretical studies were funded by the Department of Energy and the National Science Foundation’s Data Infrastructure Building Blocks (DIBBS) Local Spectroscopy Data Infrastructure program, and used resources at the San Diego Supercomputer Center provided under the Extreme Science and Engineering Discovery Environment (XSEDE).

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New cobalt-free lithium-ion battery reduces costs without sacrificing performance

For decades, researchers have looked for ways to eliminate cobalt from the high-energy batteries that power electronic devices, due to its high cost and the human rights ramifications of its mining. But past attempts haven’t lived up to the performance standards of batteries with cobalt.

Researchers from the Cockrell School of Engineering at The University of Texas at Austin say they’ve cracked the code to a cobalt-free high-energy lithium-ion battery, eliminating the cobalt and opening the door to reducing the costs of producing batteries while boosting performance in some ways. The team reported a new class of cathodes — the electrode in a battery where all the cobalt typically resides — anchored by high nickel content. The cathode in their study is 89% nickel. Manganese and aluminum make up the other key elements.

More nickel in a battery means it can store more energy. That increased energy density can lead to longer battery life for a phone or greater range for an electric vehicle with each charge.

The findings appeared this month in the journal Advanced Materials. The paper was written by Arumugam Manthiram, a professor in the Walker Department of Mechanical Engineering and director of the Texas Materials Institute, Ph.D. student Steven Lee and Ph.D. graduate Wangda Li.

Typically, increased energy density leads to trade-offs, such as a shorter cycle life — the number of times a battery can be charged and discharged before it loses efficiency and can no longer be fully charged. Eliminating cobalt usually slows down the kinetic response of a battery and leads to lower rate capability — how quickly the cathode can be charged or discharged. However, the researchers said they’ve overcome the short cycle life and poor rate capability problems through finding an optimal combination of metals and ensuring an even distribution of their ions.

Most cathodes for lithium-ion batteries use combinations of metal ions, such as nickel-manganese-cobalt (NMC) or nickel-cobalt-aluminum (NCA). Cathodes can make up roughly half of the materials costs for the entire battery, with cobalt being the priciest element. At a price of approximately $28,500 per ton, it is more expensive than nickel, manganese and aluminum combined, and it makes up 10% to 30% of most lithium-ion battery cathodes.

“Cobalt is the least abundant and most expensive component in battery cathodes,” Manthiram said. “And we are completely eliminating it.”

The key to the researchers’ breakthrough can be found at the atomic level. During synthesis, they were able to ensure the ions of the various metals remained evenly distributed across the crystal structure in the cathode. When these ions bunch up, performance degrades, and that problem has plagued previous cobalt-free, high-energy batteries, Manthiram said. By keeping the ions evenly distributed, the researchers were able to avoid performance loss.

“Our goal is to use only abundant and affordable metals to replace cobalt while maintaining the performance and safety,” Li said, “and to leverage industrial synthesis processes that are immediately scalable.”

Manthiram, Li and former postdoctoral researcher Evan Erickson worked with UT’s Office of Technology Commercialization to form a startup called TexPower to bring the technology to market. The researchers have received grants from the U.S. Department of Energy, which has sought to decrease dependency on imports for key battery materials.

Industry has jumped on the cobalt-free push — most notably an effort from Tesla to eliminate the material from the batteries that power its electric vehicles. With large government organizations and private companies focused on reducing dependence on cobalt, it’s no surprise that this pursuit has become competitive. The researchers said they have avoided problems that hindered other attempts at cobalt-free, high-energy batteries with innovations on the right combination of materials and the precise control of their distribution.

“We are increasing the energy density and lowering the cost without sacrificing cycle life,” Manthiram said. “This means longer driving distances for electric vehicles and better battery life for laptops and cellphones.”

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New lithium battery charges faster, reduces risk of device explosions

Cell phone batteries often heat up and, at times, can burst into flames. In most cases, the culprit behind such incidents can be traced back to lithium batteries. Despite providing long-lasting electric currents that can keep devices powered up, lithium batteries can internally short circuit, heating up the device.

Researchers at Texas A&M University have invented a technology that can prevent lithium batteries from heating and failing. Their carbon nanotube design for the battery’s conductive plate, called the anode, enables the safe storage of a large quantity of lithium ions, thereby reducing the risk of fire. Further, they said that their new anode architecture will help lithium batteries charge faster than current ¬¨¬¨commercially available batteries.

“We have designed the next generation of anodes for lithium batteries that are efficient at producing large and sustained currents needed to quickly charge devices,” said Juran Noh, a material sciences graduate student in Dr. Choongho Yu’s laboratory in the J. Mike Walker ’66 Department of Mechanical Engineering. “Also, this new architecture prevents lithium from accumulating outside the anode, which over time can cause unintended contact between the contents of the battery’s two compartments, which is one of the major causes of device explosions.”

Their results are published in the March issue of the journal Nano Letters.

When lithium batteries are in use, charged particles move between the battery’s two compartments. Electrons given up by lithium atoms move from one side of the battery to the other. On the other hand, lithium ions travel the other direction. When charging the battery, lithium ions and electrons go back to their original compartments.

Hence, the property of the anode, or the electrical conductor that houses lithium ions within the battery, plays a decisive role in the battery’s properties. A commonly used anode material is graphite. In these anodes, lithium ions are inserted between layers of graphite. However, Noh said this design limits the amount of lithium ions that can be stored within the anode and even requires more energy to pull the ions out of the graphite during charging.

These batteries also have a more insidious problem. Sometimes lithium ions do not evenly deposit on the anode. Instead, they accumulate on the anode’s surface in chunks, forming tree-like structures, called dendrites. Over time, the dendrites grow and eventually pierce through the material that separates the battery’s two compartments. This breach causes the battery to short circuit and can set the device ablaze. Growing dendrites also affect the battery’s performance by consuming lithium ions, rendering them unavailable for generating a current.

Noh said another anode design involves using pure lithium metal instead of graphite. Compared to graphite anodes, those with lithium metal have a much higher energy content per unit mass or energy density. But they too can fail in the same catastrophic way due to the formation of dendrites.

To address this problem, Noh and her teammates designed anodes using highly conductive, lightweight materials called carbon nanotubes. These carbon nanotube scaffolds contain spaces or pores for lithium ions to enter and deposit. However, these structures do not bind to lithium ions favorably.

Hence, they made two other carbon nanotube anodes with slightly different surface chemistry — one laced with an abundance of molecular groups that can bind to lithium ions and another that had the same molecular groups but in a smaller quantity. With these anodes, they built batteries to test the propensity to form dendrites.

As expected, the researchers found that scaffolds made with just carbon nanotubes did not bind to lithium ions well. Consequently, there was almost no dendrite formation, but the battery’s ability to produce large currents was also compromised. On the other hand, scaffolds with an excess of binding molecules formed many dendrites, shortening the battery’s lifetime.

However, the carbon nanotube anodes with an optimum quantity of the binding molecules prevented the formation of dendrites. In addition, a vast quantity of lithium ions could bind and spread along the scaffold’s surface, thereby boosting the battery’s ability to produce large, sustained currents.

“When the binding molecular groups are abundant, lithium metal clusters made from lithium ions end up just clogging the pores on the scaffolds,” said Noh. “But when we had just the right amount of these binding molecules, we could ‘unzip’ the carbon nanotube scaffolds at just certain places, allowing lithium ions to come through and bind on to the entire surface of the scaffolds rather than accumulate on the outer surface of the anode and form dendrites.”

Noh said that their top-performing anodes handle currents five times more than commercially-available lithium batteries. She noted this feature is particularly useful for large-scale batteries, such as those used in electric cars, that require quick charging.

“Building lithium metal anodes that are safe and have long lifetimes has been a scientific challenge for many decades,” said Noh. “The anodes we have developed overcome these hurdles and are an important, initial step toward commercial applications of lithium metal batteries.”

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Laying foundation for safer, longer-lasting batteries

Researchers sped-up the motion of lithium ions in solid-state batteries using the paddlewheel effect.

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Paper-thin gallium oxide transistor handles more than 8,000 volts

People love their electric cars. But not so much the bulky batteries and related power systems that take up precious cargo space.

Help could be on the way from a gallium oxide-based transistor under development at the University at Buffalo.

In a study published in the June edition of IEEE Electron Device Letters, electrical engineers describe how the tiny electronic switch can handle more than 8,000 volts, an impressive feat considering it’s about as thin as a sheet of paper.

The transistor could lead to smaller and more efficient electronic systems that control and convert electric power — a field of study known as power electronics — in electric cars, locomotives and airplanes. In turn, this could help improve how far these vehicles can travel.

“To really push these technologies into the future, we need next-generation electronic components that can handle greater power loads without increasing the size of power electronics systems,” says the study’s lead author, Uttam Singisetti, who adds that the transistor could also benefit microgrid technologies and solid-state transformers.

Singisetti, PhD, associate professor of electrical engineering at the UB School of Engineering and Applied Sciences, and students in his lab have been studying the potential of gallium oxide, including previous work exploring transistors made from the material.

Perhaps the chief reason researchers are exploring gallium oxide’s potential for power electronics is a property known as “bandgap.”

Bandgap measures how much energy is required to jolt an electron into a conducting state. Systems made with wide-bandgap materials can be thinner, lighter and handle more power than systems made of materials with lower bandgaps.

Gallium oxide’s bandgap is about 4.8 electron volts, which places it among an elite group of materials considered to have an ultrawide bandgap.

The bandgap of these materials exceeds that of silicon (1.1 electron volts), the most common material in power electronics, as well as potential replacements for silicon, including silicon carbide (about 3.4 electron volts) and gallium nitride (about 3.3 electron volts).

A key innovation in the new transistor revolves around passivation, which is a chemical process that involves coating the device to reduce the chemical reactivity of its surface. To accomplish this, Singisetti added a layer of SU-8, an epoxy-based polymer commonly used in microelectronics.

The results were impressive.

Tests conducted just weeks before the COVID-19 pandemic temporarily shuttered Singisetti’s lab in March show the transistor can handle 8,032 volts before breaking down, which is more than similarly designed transistors made of silicon carbide or gallium nitride that are under development.

“The higher the breakdown voltage, the more power a device can handle,” says Singisetti. “The passivation layer is a simple, efficient and cost-effective way to boost the performance of gallium oxide transistors.”

Simulations suggest the transistor has a field strength of more than 10 million volts (or 10 megavolts) per centimeter. Field strength measures the intensity of an electromagnetic wave in a given spot, and it eventually determines the size and weight of power electronics systems.

“These simulated field strengths are impressive. However, they need to be verified by direct experimental measurements,” Singisetti says.

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Computer vision helps scientists study lithium ion batteries

Lithium-ion batteries lose their juice over time, causing scientists and engineer to work hard to understand that process in detail. Now, scientists at the Department of Energy’s SLAC National Accelerator Laboratory have combined sophisticated machine learning algorithms with X-ray tomography data to produce a detailed picture of how one battery component, the cathode, degrades with use.

The new study, published May 8 in Nature Communications, focused on how to better visualize what’s going on in cathodes made of nickel-manganese-cobalt, or NMC. In these cathodes, NMC particles are held together by a conductive carbon matrix, and researchers have speculated that one cause of performance decline could be particles breaking away from that matrix. The team’s goal was to combine cutting-edge capabilities at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) and the European Synchrotron Radiation Facility (ESRF) to develop a comprehensive picture of how NMC particles break apart and break away from the matrix and how that might contribute to performance losses.

Of course, it’s a tall order for humans to figure out what’s going on just by looking at pictures of an NMC cathode, so the team turned to computer vision, a subfield of machine learning algorithms originally designed to scan images or videos and identify and track objects like dogs or cars.

Even then, there were challenges. Computer vision algorithms often zero in on boundaries defined by light or dark lines, so they’d have a hard time differentiating between several small NMC particles stuck together and a single large but partially fractured one; to most computer vision systems, those fractures would look like clean breaks.

To address that problem, the team used a type of algorithm set up to deal with hierarchical objects — for example, a jigsaw puzzle, which we would think of as a complete entity even though it’s made up of many individual pieces. With input and judgments from the researchers themselves, they trained this algorithm to distinguish different kinds of particles and thus develop a three-dimensional picture of how NMC particles, whether large or small, fractured or not, break away from the cathode.

They discovered that particles detaching from the carbon matrix really do contribute significantly to a battery’s decline, at least under conditions one would typically see in consumer electronics, such as smart phones.

Second, while large NMC particles are more likely to become damaged and break away, quite a few smaller particles break away, too, and overall, there’s more variation in the way small particles behave, said Yijin Liu, a staff scientist at SLAC and a senior author of the new paper. That’s important because researchers had generally assumed that by making battery particles smaller, they could make longer-lasting batteries — something the new study suggests might not be so straightforward, Liu said.

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Supercapacitor promises storage, high power and fast charging

A new supercapacitor based on manganese oxide could combine the storage capacity of batteries with the high power and fast charging of other supercapacitors, according to researchers at Penn State and two universities in China.

“Manganese oxide is definitely a promising material,” said Huanyu “Larry” Cheng, assistant professor of engineering science and mechanics and faculty member in the Materials Research Institute, Penn State. “By combining with cobalt manganese oxide, it forms a heterostructure in which we are able to tune the interfacial properties.”

The group started with simulations to see how manganese oxide’s properties change when coupled with other materials. When they coupled it to a semiconductor, they found it made a conductive interface with a low resistance to electron and ion transport. This will be important because otherwise the material would be slow to charge.

“Exploring manganese oxide with cobalt manganese oxide as a positive electrode and a form of graphene oxide as a negative electrode yields an asymmetric supercapacitor with high energy density, remarkable power density and excellent cycling stability,” according to Cheng Zhang, who was a visiting scholar in Cheng’s group and is the lead author on a paper published recently in Electrochimica Acta.

The group has compared their supercapacitor to others and theirs has much higher energy density and power. They believe that by scaling up the lateral dimensions and thickness, their material has the potential to be used in electric vehicles. So far, they have not tried to scale it up. Instead, their next step will be to tune the interface where the semiconducting and conducting layers meet for even better performance. They want to add the supercapacitor to already developed flexible, wearable electronics and sensors as an energy supply for those devices or directly as self-powered sensors.

The National Natural Science Foundation of China and the Science Research Fund of Guizhou Province, China supported this research.

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