MechSE Associate Professor Kyle Smith and doctoral student Md Abdul Hamid recently published an article in the Journal of Power Sources.

Their study, “A bottom-up, multi-scale theory for transient mass transport of redox-active species through porous electrodes beyond the pseudo-steady limit,” demonstrates that conventional theory approaches underpredict the power capacity of flow batteries such as those used in electricity production from renewable energy sources.

“We have discovered a new means by which to understand how convection occurs inside of reactive porous media,” Smith said of their theory, which proposes introducing certain frequency-dependent transfer functions to up-scale mass transport occurring in the microscopic pores of electrodes. Although transfer functions are routinely used as mathematical tools in control theory, they have never before been applied in this context or derived in this manner.

The two began formulating their theory before the COVID-19 outbreak, making their publication a long-anticipated success. Their theory sheds new light on familiar mass and heat transfer principles—they introduced a spectral Sherwood number, which is a type of transfer function, to extend the film law of mass transfer to transient conditions. Similarly, a spectral Nusselt number extends Newton’s law of cooling for convection heat transfer. The two formulated the embedding of transfer functions into an up-scaled model to obtain the time-domain response of flow batteries.

“We have uncovered a new understanding of certain non-dimensional parameters that are ubiquitous in convection heat/mass transfer,” Smith said. “For the first time to our knowledge, we have extended these ideas from their conventional application in time-invariant, or steady state, settings to transient settings in a manner that accounts for changes in the microscopic dynamics that result from transient cycling.”

This work is also meaningful to chemical, civil, and petroleum engineering communities, which have explored approaches to understanding mass transfer in other porous materials. “Their approaches were not previously applied to the electrochemical systems that are the subject of our work,” Smith said. “However, we have developed a relatively straightforward approach to model these effects by using a formulation that starts from the detailed microstructure and up-scales its effects for use in macroscopic scale models.”

Indeed, the team’s theory demonstrates that flow batteries can be operated at higher than their limiting current for short periods of time, which suggests that cheaper and lighter batteries can be designed for these cycling conditions.

“These findings not only provide a better modeling approach for accurate prediction of an existing flow battery’s rate capability, but also provide guidelines toward more efficient designs, operating schemes, and materials,” Hamid said.

Smith and Hamid intend to apply their theory to different microstructures for porous electrodes for various energy and environmental devices using electrochemistry. Their next steps also include extending the theory beyond the range of conditions demonstrated in their publication.

Recognizing when senior citizens are at risk in the home or helping them find misplaced objects they presumed lost: The technology developed in the successful OMNICONNECT project can help people lead independent lives for longer. The researchers of Fraunhofer IZM have integrated a miniature radar system into an LED ceiling light that can track and recognize movement patterns and locate people or objects in a room.

Four radar modules are combined to ensure full 360° coverage. AI algorithms work through the collected data to identify whether a person in that range has suffered a fall, with the radar system being able to track more than 30 people in spaces of up to 1600 square feet with an angular resolution of 12°. And for added object detection capabilities, passive transponders were developed to work with the radar system.

Supported by the Ministry of Education and Research, the OMNICONNECT project has brought together researchers from the Fraunhofer Institute for Reliability and Microintegration IZM with partners from Berlin and Oldenburg.

Their mission: To develop a miniature radar system that can detect medical emergencies or other situations that require a caregiver’s intervention, while respecting the privacy of the users. By contrast to cameras or CCTV systems that record images, the system only tracks patterns of movement. It is integrated into a ceiling light, making it easy to install, unobtrusive, and easy to accept for the people living with it.

The system works with AI-supported radar modules and passive transponders that can be placed on different objects, thus for the first time enabling the tracking of movement and location with a single radar system. The transponders work as frequency-specific radar targets, with each resonating at a known frequency. This turns them into uniquely identifiable beacons that the system can scan for and whose precise location can be calculated by checking the time needed for the signal to bounce back.

The data is processed on site by a field-programmable gate array or FPGA, a tiny computing system with integrated processor. It shares the object and motion data with an AI-based system that can recognize movements and patterns, developed by the computer science researchers at the OFFIS Institute of the University of Oldenburg. To control the app and identify specific options, a special app interface was built by HFC Human-Factors-Consult GmbH.

The demonstration unit designed and constructed at Fraunhofer IZM has undergone live trials and proven its ability to detect an object’s position with an accuracy of five centimeters in a ten-meter range. The demonstrator is currently being used by the project partners in several possible use cases. The data it collects can be used to produce certain movement patterns of typical behaviors and, with enough meaningful data available, feed into possible assisted living applications or be used to recognize certain incidents. The position data could be used to check whether the detected person is feeling well or whether a medical or care intervention is indicated.

Large-scale, effective, and passive: these descriptions are aptly given to the integrated radiative and evaporative chiller (IREC), designed and tested by researchers at Tsinghua University in Beijing, China. The goal of this technology is to come up with an energetically affordable method of cooling to aid in the rising consumption of energy while still minimizing carbon emissions through the process.

“Energy scarcity is a universal challenge to global development. The demand for cooling has accounted for more than 10% of the total global electricity consumption, and the trend is increasing year by year,” said Liangti Qu, author of the paper and researcher at Tsinghua University.

In efforts to find a solution to a rising energy challenge, researchers worked to develop IREC. IREC works in tandem with a couple of partners, which include a polyacrylamide hydrogel layer and breathable, reflective fibers on the surface to reflect light. The hydrogel layer aids in speeding up the evaporation process as well as keeping the energy input from the sun minimized.

The reflective fibers can keep the energy from solar radiation from heating the water and are shown to be effective against high angles of light, making it effective during all parts of the day in all regions of the world.

The report was published in Nano Research Energy.

During their study, the researchers found that IREC can reduce the heat inside outdoor storage items by more than 9 ºC, making it an appealing option for outdoor cooling options.

“This technology can achieve cooling powers of over 700 W·m^–2, several times that of a single radiative cooling process. Besides, the working mode is compatible with the existing central heating equipment and can be used for central cooling in summer by supplying cold water. It promises to be a sustainable alternative to current cooling needs,” Qu said.

Additionally, it was shown that up to 69.2% of the heat consumed by IREC came from the environment. The IREC technology absorbs heat from the environment, thereby cooling it through evaporation. As if the technology wasn’t appealing enough in its efforts to be sustainable and cost-effective, the ability to set the IREC up on existing central heating equipment reduces the barrier to entry for those wishing for a more sustainable, energy-efficient cooling method.

The experiment also ran multiple tests to determine how well the radiative and evaporative cooling technique works under various conditions, such as indoor and outdoor use, and even use on the human body to aid in cooling.

On human skin, IREC mimics the sweat reaction humans have to keep cool under hot conditions and can assist in cooling the body by 13º C for over 12 hours. The wide application of this technology for not only commercial use but also personal use makes it even more appealing to researchers to continue to develop and streamline the process for wide-scale production.

Finding methods of cooling that are both cost and energy efficient will continue to be a challenge, especially to make them affordable and available on a large scale. Ideally, once the prototype is streamlined and optimized, the researchers want to see this integrated cooling technology commercially available for use in “green” buildings and industrial storage facilities.

Provided by
Tsinghua University Press

Food delivery platform Just Eat Takeaway unveiled plans Tuesday to axe more than 1,700 mostly courier jobs in Britain, as it slashes costs in the wake of huge annual losses.

The UK business “is reorganising and simplifying its delivery operation as part of the ongoing goal of improving efficiency”, it said in a statement emailed to AFP.

“As part of this process we have proposed to transition away from the worker model for couriers” in Britain, it added.

Just Eat Takeaway said its UK division will stop employing its own couriers—and instead will only use self-employed gig economy workers.

Approximately 170 staff in its UK operations team will also be affected by the overhaul, but some could be redeployed.

Just Eat Takeaway had revealed earlier this month that acquisition writedowns, the souring economic climate and rising interest rates sparked a massive loss of about 5.7 billion euros ($6.1 billion) last year.

The Amsterdam-based company was created in 2020 after Dutch online service Takeaway.com gobbled up Britain’s Just Eat, and business subsequently boomed on the back of the COVID pandemic-fuelled surge in home delivery, which has since subsided.

The group has also put Grubhub up for sale as it seeks to focus on Europe, having already slashed the value of the US subsidiary it bought for $7.3 billion in 2020.

© 2023 AFP

Concrete is the most used material in the construction industry and dates to the Roman Empire. Engineers at the University of Pittsburgh are now reimagining its design for the 21st century.

New research introduces metamaterial concrete for the development of smart civil infrastructure systems. The paper, “Multifunctional Nanogenerator-Integrated Metamaterial Concrete Systems for Smart Civil Infrastructure,” presents a new concept for lightweight and mechanically-tunable concrete systems that have integrated energy harvesting and sensing functionality.

“Modern society has been using concrete in construction for hundreds of years, following its original creation by the ancient Romans,” said Amir Alavi, assistant professor of civil and environmental engineering at Pitt, who is the corresponding author on the study. “Massive use of concrete in our infrastructure projects implies the need for developing a new generation of concrete materials that are more economical and environmentally sustainable, yet offer advanced functionalities. We believe that we can achieve all of these goals by introducing a metamaterial paradigm into the development of construction materials.”

Alavi and his team have previously developed self-aware metamaterials and explored their use in applications like smart implants.

This study introduces the use of metamaterials in the creation of concrete, making it possible for the material to be specifically designed for its purpose. Attributes like brittleness, flexibility and shapeability can be fine-tuned in the creation of the material, enabling builders to use less of the material without sacrificing strength or longevity.

“This project presents the first composite metamaterial concrete with super compressibility and energy harvesting capability,” said Alavi. “Such lightweight and mechanically tunable concrete systems can open a door to the use of concrete in various applications such as shock absorbing engineered materials at airports to help slow runaway planes or seismic base isolation systems.”

Not only that, but the material is capable of generating electricity. While it cannot produce enough electricity to send power to the electrical grid, the generated signal will be more than enough to power the roadside sensors. The electrical signals self-generated by the metamaterial concrete under mechanical excitations can also be used to monitor damage inside the concrete structure or to monitor earthquakes while reducing their impact on buildings.

Eventually, these smart structures may even power chips embedded inside roads to help self-driving cars navigate on highways when GPS signals are too weak or LIDAR is not working.

The material is composed of reinforced auxetic polymer lattices embedded in a conductive cement matrix. The composite structure induces contact-electrification between the layers when triggered mechanically. The conductive cement, which is enhanced with graphite powder, serves as the electrode in the system. Experimental studies show that the material can compress up to 15% under cyclic loading and produce 330 μW of power.

The research team is partnering with the Pennsylvania Department of Transportation (PennDOT) through the IRISE Consortium at Pitt to develop this metamaterial concrete for use on Pennsylvania roads.

The paper, “Multifunctional Nanogenerator-Integrated Metamaterial Concrete Systems for Smart Civil Infrastructure,” was published in Advanced Materials.

A recent study that examined the relationship between artificial intelligence (AI) and law enforcement underscores both the need for law enforcement agencies to be involved in the development of public policies regarding AI—such as regulations governing autonomous vehicles—and the need for law enforcement officers to better understand the limitations and ethical challenges of AI technologies.

“Law enforcement agencies have a crucial role to play in implementing public policies related to AI technologies,” says Veljko Dubljević, corresponding author of the study and an associate professor of science, technology and society at North Carolina State University.

“For example, officers will need to know how to proceed if they pull over a vehicle being driven autonomously for a traffic violation. For that matter, they will need to know how to pull over a vehicle being driven autonomously. Because of their role in maintaining public order, it’s important for law enforcement to have a seat at the table in crafting these policies.”

“In addition, there are a number of AI-powered technologies that are already in use by law enforcement agencies that are designed to help them prevent and respond to crime,” says Ronald Dempsey, first author of the study and a former graduate student at NC State. “These range from facial recognition technologies to technologies designed to detect gunshots and notify relevant law enforcement agencies.”

“However, our study suggests that many officers do not understand how these technologies work, which makes it difficult or impossible for them to appreciate the limitations and ethical risks of those technologies. And that can pose significant problems for both law enforcement and the public.”

For this study, the researchers conducted in-depth interviews with 20 law enforcement professionals who work in North Carolina. The interviews addressed a range of issues, including the values and qualities that the study participants felt were critical for law enforcement officers.

While there was no consensus across a majority of study participants, there were several characteristics that cropped up repeatedly as important qualities for a law enforcement professional, with integrity, honesty and empathy being cited most often.

“Understanding what law enforcement deems to be desirable characteristics in officers is valuable, because these characteristics can inform the development of responsible design guidelines for AI technologies that law enforcement will use,” Dempsey says.

“Design guidelines can be used to inform AI decision-making, and it is easier for end users to work with AI tools if the values guiding AI decisions are consistent—or at least not in conflict—with the values of the end users,” says Dubljević.

The researchers also asked study participants about their views on AI in general, as well as existing and emerging AI technologies.

“We found that study participants were not familiar with AI, or with the limitations of AI technologies,” says Jim Brunet, co-author of the study and director of NC State’s Public Safety Leadership Initiative. “This included AI technologies that participants had used on the job, such as facial recognition and gunshot detection technologies. However, study participants expressed support for these tools, which they felt were valuable for law enforcement.”

The study participants also expressed concern about the future of autonomous vehicles, and what challenges they may pose to the law enforcement community.

“However, study participants did say that they would welcome public use of autonomous vehicles if that would reduce car accidents,” says Dubljević. “Specifically, the participants welcomed the idea of spending less time responding to vehicle accidents, which would allow them to focus on addressing crime.”

“There are always dangers when law enforcement adopts technologies that were not developed with law enforcement in mind,” says Brunet. “This certainly applies to AI technologies such as facial recognition. As a result, it’s critical for law enforcement officials to have some training in the ethical dimensions surrounding the use of these AI technologies. For example, where a law enforcement agency chooses to deploy AI tools will affect which portions of the public are subject to additional scrutiny.”

“It’s also important to understand that AI tools are not foolproof,” says Dubljević. “AI is subject to limitations. And if law enforcement officials don’t understand those limitations, they may place more value on the AI than is warranted—which can pose ethical challenges in itself.”

The paper is published in the journal Applied Sciences.

Unmanned aerial vehicles (UAVs), also known as drones, can help humans to tackle a variety of real-world problems; for instance, assisting them during military operations and search and rescue missions, delivering packages or exploring environments that are difficult to access. Conventional UAV designs, however, can have some shortcomings that limit their use in particular settings.

For instance, some UAVs might be unable to land on uneven terrains or pass through particularly narrow gaps, while others might consume too much power or only operate for short amounts of time. This makes them difficult to apply to more complex missions that require reliably moving in changing or unfavorable landscapes.

Researchers at Zhejiang University have recently developed a new unmanned, wheeled and hybrid vehicle that can both roll on the ground and fly. This unique system, introduced in a paper pre-published on arXiv, is based on a unicycle design (i.e., a cycling vehicle with a single wheel) and a rotor-assisted turning mechanism.

“Roller-Quadrotor is a novel hybrid terrestrial and aerial quadrotor that combines the elevated maneuverability of the quadrotor with the lengthy endurance of the ground vehicle,” Zhi Zheng, Jin Wang and their colleagues wrote in their paper. “Flying is achieved through a quadrotor configuration, and four actuators providing thrust. Rolling is supported by unicycle-driven and rotor-assisted turning structure. During terrestrial locomotion, the vehicle needs to overcome rolling and turning resistance, thus saving energy compared to flight mode.”

The hybrid terrestrial and aerial vehicle created by Zheng, Wang and their colleagues is a so-called quadrotor, which is an aircraft based on rotary wings that can hover above ground and fly. As it is based on a unicycle structure, it can also move on the ground on various terrains and pass through narrow gaps.

“This work overcomes the challenging problems of general rotorcraft, reduces energy consumption and allows movement through special terrains, such as narrow gaps,” the researchers wrote in their paper. “It also solves the obstacle avoidance challenge faced by terrestrial robots by flying.”

In their paper, Zheng, Wang and their colleagues present their vehicle’s design along with a series of models and controllers that allow it to roll, fly, and seamlessly transition between these two modes of operation. They also outline the results of a series of experiments, where a prototype of their vehicle was tested in an environment monitored by cameras and motion capture sensors.

“We design the models and controllers for the vehicle,” Zheng, Wang and their colleagues wrote in their paper. “The experiment results show that it can switch between aerial and terrestrial locomotion, and be able to safely pass through a narrow gap half the size of its diameter. Besides, it is capable of rolling a distance approximately 3.8 times as much as flying or operating about 42.2 times as lengthy as flying.”

The hybrid vehicle presented in this recent paper could soon be tested and evaluated in a wider range of environments, to further validate its performance. Initial results gathered by Zheng, Wang and their colleagues suggest that the vehicle could eventually be used to tackle complex real-world missions that entail moving on tricky terrains, entering narrow passages and operating for longer periods of time.

In their next studies, the researchers plan to enhance their design further, for instance by improving the accuracy of the models they created and introducing more advanced control algorithms. This could in turn make the vehicle’s transition from its rolling to flying modes smoother, while also improving its navigation capabilities.

“We are also considering structural optimization and weight reduction, to further improve the energy consumption performance,” the researchers concluded in their paper. “Furthermore, we will use planning algorithms to enhance vehicle mobility.”

© 2023 Science X Network

The last gas-powered muscle car from Dodge isn’t leaving the road without some squeals, thunder and crazy-fast speed.

The 2023 Challenger SRT Demon 170 will deliver 1,025 horsepower from its 6.2-liter supercharged V-8, and the automaker says it will be the quickest production car made.

Stellantis says it can go from zero to 60 miles per hour (97 kilometers per hour) in a scary 1.66 seconds, making it faster than even electric supercars from Tesla and Lucid.

It’s what the performance brand from Stellantis is calling the last of the rumbling cars that for decades were a fixture of American culture on Saturday night cruises all over the country.

Stellantis will stop making gas versions of the Dodge Challenger and Charger and the Chrylser 300 big sedan by the end of this year, squeezed out by stricter government fuel-economy regulations and an accelerating shift to electric vehicles to fight climate change.

The Canadian factory that makes all three cars will be retooled to make electric versions of larger cars starting next year. Stellantis hasn’t said whether all three models will survive, but it did show off a Charger Daytona SRT electric concept muscle car back in August.

Tim Kuniskis, CEO of the Dodge brand and the unofficial spokesman for America’s gas-powered rubber-burners, said that, while he’ll miss the traditional muscle, he’s excited about making electric performance vehicles.

“It’s the end of an era, for sure,” he said Monday. “Electric products, they’re very fast. Muscle cars, one of the primary ingredients is to be a fast accelerating car. So I’ve automatically got the power. Now I’ve just got to figure out ways to bring all the other elements in of the excitement of the driving experience.”

Since last summer, Dodge has been rolling out powerful special-edition “Last Call” versions of its gas powered muscle cars, culminating with an event Monday night to show the Challenger Demon 170 at the Las Vegas Motor Speedway drag strip.

The new Challenger Demon, a descendant of a car that first went on sale in 1969, also produces 945 pound-feet of torque, or rotational force—so much power that the company had to strengthen the rear drive shaft and differential with aerospace-grade metals.

According to Stellantis, the car will be the first production vehicle to run a quarter-mile (0.40 kilometers) in under nine seconds—8.91 to be exact. To do that, it hits a speed of just over 151 mph (243 kilometers per hour). Horsepower and speed depends on how much ethanol is in the fuel.

It gets only 13 miles per gallon in the city and 21 on the highway, but it’s doubtful anyone buying one will care even as the world deals with climate change.

Kuniskis says it’s a relatively small number of cars, and he says the ethanol they burn is cleaner than gasoline. Dodge, he said, will have built 2 million muscle cars by the time production of gas versions ends Dec. 31. Dodge’s followers, he said, deserve a celebration.

“After all these years, we owed it as much to them as to ourselves to celebrate this end, and give them something that produces a lot of pride in the brand that they love,” he said.

The Demon 170 is street legal, even though it comes with wide racing tires . To make it a daily driver, the company is offering a package of smaller, more street friendly wheels and tires.

At a devilish $96,666, the car comes standard with only a driver’s seat and a basic radio. But it has air conditioning. Front passenger and back seats are optional for $1 each. You can also get leather, a sunroof and a better sound system.

Stellantis will make only up to 3,300 of them, and Kuniskis isn’t sure if they’ll hit that number due to potential parts shortages and a limited production time.

If previous limited-edition models are any indication, the Demon 170 should become an instant classic collector’s car, Kuniskis said.

“If you look at some of the cars that we’ve had in our past, it’s pretty easy to tell which ones people want to collect,” he said. “A lot of times it’s the lower (sales) volume, extreme examples, whether its extreme looks or extreme performance. Well, this one happens to have both.”

© 2023 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.

Attackers have the ability not only to manipulate software, but also to tamper with the hardware. A team from Bochum is devising methods to detect such tampering.

Security gaps exist not only in software, but also directly in hardware. Attackers might deliberately have them built in in order to attack technical applications on a large scale. Researchers at Ruhr University Bochum, Germany, and the Max Planck Institute for Security and Privacy (MPI-SP) in Bochum are exploring methods of detecting such so-called hardware Trojans. They compared construction plans for chips with electron microscope images of real chips and had an algorithm search for differences. This is how they detected deviations in 37 out of 40 cases.

The team at the CASA Cluster of Excellence (short for Cyber Security in the Age of Large-Scale Adversaries), headed by Dr. Steffen Becker, and the MPI-SP team headed by Endres Puschner, will present their findings at the IEEE Symposium on Security and Privacy, which will take place in San Francisco from 22 to 25 May 2023. The research was conducted in collaboration with Thorben Moos from the Université catholique de Louvain (Belgium) and the Federal Criminal Police Office in Germany.

The researchers released all images of the chips, the design data as well as the analysis algorithms online for free so that other research groups can use the data to conduct further studies. A preprint of the paper is also published as part of the Proceedings of the IEEE Symposium on Security and Privacy.

Manufacturing plants as a gateway for hardware Trojans

These days, electronic chips are integrated into countless objects. They are more often than not designed by companies that don’t operate their own production facilities. The construction plans are therefore sent to highly specialized chip factories for production.

“It’s conceivable that tiny changes might be inserted into the designs in the factories shortly before production that could override the security of the chips,” explains Steffen Becker and gives an example for the possible consequences: “In extreme cases, such hardware Trojans could allow an attacker to paralyze parts of the telecommunications infrastructure at the push of a button.”

Identifying differences between chips and construction plans

Becker and Puschner’s team analyzed chips produced in the four modern technology sizes of 28, 40, 65 and 90 nanometers. For this purpose, they collaborated with Dr. Thorben Moos, who had designed several chips as part of his Ph.D. research at Ruhr University Bochum and had them manufactured. Thus, the researchers had both the design files and the manufactured chips at their disposal. They obviously couldn’t modify the chips after the fact and build in hardware Trojans. And so they employed a trick: rather than manipulating the chips, Thorben Moos changed his designs retroactively in order to create minimal deviations between the construction plans and the chips. Then, the Bochum researchers tested if they could detect these changes without knowing what exactly they had to look for and where.

In the first step, the team at Ruhr University Bochum and MPI-SP had to prepare the chips using complex chemical and mechanical methods in order to take several thousand images of the lowest chip layers with a scanning electron microscope. These layers contain several hundred thousand of the so-called standard cells that carry out logical operations.

“Comparing the chip images and the construction plans turned out to be quite a challenge, because we first had to precisely superimpose the data,” says Endres Puschner. In addition, every little impurity on the chip could block the view of certain sections of the image. “On the smallest chip, which is 28 nanometers in size, a single speck of dust or a hair can obscure a whole row of standard cells,” says the IT security expert.

Almost all manipulations detected

The researchers used image processing methods to carefully match standard cell for standard cell and looked for deviations between the construction plans and the microscopic images of the chips. “The results give cause for cautious optimism,” says Puschner.

For chip sizes of 90, 65 and 40 nanometers, the team successfully identified all modifications. The number of false-positive results totaled 500, i.e. standard cells were flagged as having been modified, although they were in fact untouched.

“With more than 1.5 million standard cells examined, this is a very good rate,” says Puschner. It was only with the smallest chip of 28 nanometers that the researchers failed to detect three subtle changes.

Higher detection rate through clean room and optimized algorithms

A better recording quality could remedy this problem in the future. “Scanning electron microscopes do exist that are specifically designed to take chip images,” points out Becker. Moreover, using them in a clean room where contamination can be prevented would increase the detection rate even further.

“We also hope that other groups will use our data for follow-up studies,” as Steffen Becker outlines potential future developments. “Machine learning could probably improve the detection algorithm to such an extent that it would also detect the changes on the smallest chips that we missed.”

In our daily lives, lithium-ion batteries have become indispensable. They function only because of a passivation layer that forms during their initial cycle. As researchers at Karlsruhe Institute of Technology (KIT) found out via simulations, this solid electrolyte interphase develops not directly at the electrode but aggregates in the solution. Their study has been published in the journal Advanced Energy Materials. Their findings allow the optimization of the performance and lifetime of future batteries.

From smartphones to electric cars—wherever a mobile energy source is required—it is almost always a lithium-ion battery that does the job. An essential part of the reliable function of this and other liquid electrolyte batteries is the solid electrolyte interphase (SEI). This passivation layer forms when voltage is applied for the first time. The electrolyte is being decomposed in the immediate vicinity of the surface. Until now, it remained unclear how the particles in the electrolytes form a layer that is up to 100 nanometers thick on the surface of the electrode since the decomposition reaction is only possible within a few nanometers distance from the surface.

The passivation layer on the anode surface is crucial to the electrochemical capacity and lifetime of a lithium-ion battery because it is highly stressed with every charging cycle. When the SEI is broken up during this process, the electrolyte is further decomposed and the battery’s capacity is reduced—a process that determines the lifetime of a battery. With the right knowledge of the SEI’s growth and composition, the properties of a battery can be controlled. But so far, no experimental or computer-aided approach was sufficient to decipher the SEI’s complex growth processes that take place on a very wide scale and in different dimensions.

Researchers at the KIT Institute of Nanotechnology (INT) have now managed to characterize the formation of the SEI with a multi-scale approach. “This solves one of the great mysteries regarding an essential part of all liquid electrolyte batteries—especially the lithium-ion batteries we all use every day,” says Professor Wolfgang Wenzel, director of the research group “Multiscale Materials Modelling and Virtual Design” at INT, which is involved in the large-scale European research initiative BATTERY 2030+ that aims to develop safe, affordable, long-lasting, sustainable high-performance batteries for the future.

More than 50,000 simulations for different reaction conditions

To examine the growth and composition of the passivation layer at the anode of liquid electrolyte batteries, the researchers at INT generated an ensemble of more than 50,000 simulations representing different reaction conditions. They found that the growth of the organic SEI follows a solution-mediated pathway. First, SEI precursors that are formed directly at the surface join far away from the electrode surface via a nucleation process. The subsequent rapid growth of the nuclei leads to the formation of a porous layer that eventually covers the electrode surface.

These findings offer a solution to the paradoxical situation that SEI constituents can form only near the surface, where electrons are available, but their growth would stop once this narrow region is covered. “We were able to identify the key reaction parameters that determine SEI thickness,” explains Dr. Saibal Jana, postdoc at INT and one of the authors of the study.

“This will enable the future development of electrolytes and suitable additives that control the properties of the SEI and optimize the battery’s performance and lifetime.”