Lithium News

What if a common element, rather than scarce expensive ones, was a key component in electric car batteries? A collaboration co-led by an Oregon State University chemistry researcher is hoping to spark a green battery revolution by showing that iron instead of cobalt and nickel can be used as a cathode material in lithium-ion batteries.

The findings, published in Science Advances, are important for multiple reasons, Oregon State’s Xiulei “David” Ji notes.

“We’ve transformed the reactivity of iron metal, the cheapest metal commodity,” he said. “Our electrode can offer a higher energy density than the state-of-the-art cathode materials in electric vehicles. And since we use iron, whose cost can be less than a dollar per kilogram—a small fraction of nickel and cobalt, which are indispensable in current high-energy lithium-ion batteries—the cost of our batteries is potentially much lower.”

At present, the cathode represents 50% of the cost in making a lithium-ion battery cell, Ji said. Beyond economics, iron-based cathodes would allow for greater safety and sustainability, he added.

As more and more lithium-ion batteries are manufactured to electrify the transportation sector, global demand for nickel and cobalt has soared. Ji points out that in a matter of a couple of decades, predicted shortages in nickel and cobalt will put the brakes on battery production as it’s currently done.

In addition, those elements’ energy density is already being extended to its ceiling level—if it were pushed further, oxygen released during charging could cause batteries to ignite—plus cobalt is toxic, meaning it can contaminate ecosystems and water sources if it leaches out of landfills.

Put it all together, Ji said, and it’s easy to understand the global quest for new, more sustainable battery chemistries.

A battery stores power in the form of chemical energy and through reactions converts it to the electrical energy needed to power vehicles as well as cellphones, laptops and many other devices and machines. There are multiple types of batteries, but most of them work the same basic way and contain the same basic components.

A battery consists of two electrodes—the anode and cathode, typically made of different materials—as well as a separator and electrolyte, a chemical medium that allows for the flow of electrical charge. During battery discharge, electrons flow from the anode into an external circuit and then collect at the cathode.

In a lithium-ion battery, as its name suggests, a charge is carried via lithium ions as they move through the electrolyte from the anode to the cathode during discharge, and back again during recharging.

“Our iron-based cathode will not be limited by a shortage of resources,” said Ji, explaining that iron, in addition to being the most common element on Earth as measured by mass, is the fourth-most abundant element in the Earth’s crust. “We will not run out of iron ’til the sun turns into a red giant.”

Ji and collaborators from multiple universities and national laboratories increased the reactivity of iron in their cathode by designing a chemical environment based on a blend of fluorine and phosphate anions—ions that are negatively charged.

The blend, thoroughly mixed as a solid solution, allows for the reversible conversion—meaning the battery can be recharged—of a fine mixture of iron powder, lithium fluoride and lithium phosphate into iron salts.

“We’ve demonstrated that the materials design with anions can break the ceiling of energy density for batteries that are more sustainable and cost less,” Ji said.

“We’re not using some more expensive salt in conjunction with iron—just those the battery industry has been using and then iron powder. To put this new cathode in applications, one needs to change nothing else—no new anodes, no new production lines, no new design of the battery. We are just replacing one thing, the cathode.”

Storage efficiency still needs to be improved, Ji said. Right now, not all of the electricity put into the battery during charging is available for use upon discharge. When those improvements are made, and Ji expects they will be, the result will be a battery that works much better than ones currently in use while costing less and being greener.

“If there is investment in this technology, it shouldn’t take long for it to be commercially available,” Ji said. “We need the visionaries of the industry to allocate resources to this emerging field. The world can have a cathode industry based on a metal that’s almost free compared to cobalt and nickel. And while you have to work really hard to recycle cobalt and nickel, you don’t even have to recycle iron—it just turns into rust if you let it go.”

The research was co-led by Tongchao Liu of Argonne National Laboratory and included Oregon State’s Mingliang Yu, Min Soo Jung and Sean Sandstrom.

Scientists from Vanderbilt University, Stanford University, the University of Maryland, Lawrence Berkeley National Laboratory and the SLAC National Accelerator Laboratory also contributed.

Starting in 2035, the European Union (EU) will prohibit the sale of internal combustion engine vehicles powered by gasoline or diesel, except for newly manufactured cars that utilize electrofuels (e-fuels, manufactured using green hydrogen obtained through electrolysis using renewable energy with carbon dioxide captured from the air). Considered as “clean fuels,” electrofuels are expected to contribute to the reduction of carbon emissions in the transportation sector.

In this regard, a breakthrough has been achieved in Korea with the development of a microchannel reactor that can produce electrofuels comparable to diesel. A microchannel reactor is a reactor composed of very small channels, and is a highly efficient system that performs chemical reactions through these channels. This reactor facilitates the efficient transfer of heat.

This innovative technology not only converts carbon dioxide into diesel-like fuels, making it a viable solution for future international fuel standards, but also holds promise for various industries requiring heat management, including electrofuel production and ammonia synthesis.

The research team led by Principal Researcher Young Kim from the Heat Pump Research Center of the Research Institute of Carbon-neutral Energy Machinery of the Korea Institute of Machinery and Materials (KIMM) has successfully developed a highly efficient microchannel reactor which reduces the required catalyst amount to 30% for electrofuel production, yet offers a capacity 30 times greater than current reactors.

This reactor is safe at high temperature and pressure and is easy to remove heat, so the temperature setting is flexible, making it advantageous for e-fuel production.

The design of battery technologies with increasingly longer lifespans could help to meet the growing needs of the electronics and automotive industry. Lithium (Li) batteries are the most widely used rechargeable batteries worldwide. Thus, devising strategies that can increase their longevity could be far easier than designing entirely new batteries.

Li-metal batteries, batteries with a Li metal anode, are among the most promising next-generation battery designs. Nonetheless, the reactivity of Li metal has so far greatly limited their cycling stability, by impairing the formation of stable solid-electrolyte interphases (SEIs), ultimately resulting in shorter battery lifespans.

Researchers at the Pennsylvania State University, University of Illinois Chicago and Argonne National Laboratory have recently introduced a new method to extend the longevity of Li-metal batteries. This method, introduced in a paper published in Nature Energy, relies on the use of a highly fluorinated cyclic ether (3,3,4,4,5,5-hexafluorotetrahydropyran, HFTHP), which exhibits a limited reactivity to Li metal ions and can thus improve the stability of formed SEIs.

“Extending the lifespan of lithium (Li) batteries involves managing reactions at the Li anode and stabilizing the solid–electrolyte interphase (SEI) through strategic regulation of the electrolyte composition,” Guo-Xing Li, Volodymyr Koverga and their colleagues wrote in their paper. “We synthesized a fluorinated cyclic ether with minimized Li-ion coordination capability and enhanced electrochemical stability. We demonstrated its crucial role in manipulating the SEI formation process by differentiating the contribution of dual anions to the SEI layer.”

A crucial difference between the ether they synthesized and previously proposed linear fluorinated ethers, such as BTFE and TTE, is that it exhibits a minimized coordination to Li ions. This facilitates the formation of an inorganic-dominant bilayer SEI in metal-ion batteries, composed of a Li₂O-rich inner layer and a LiF-rich outer layer.

This SEI was found to significantly boost the stability and reversibility of Li-metal anodes. The resulting Li-metal battery cells have a remarkably long cycling life, improved self-discharge capabilities and high-temperature performance.

Li, Koverga and their colleagues used the ether to design a liquid electrolyte for Li-metal batteries composed of 1 M LiDFOB and 0.4 M LiBF₄ in dimethoxyethane (DME)/HFTHP. They found that their design achieved exceptional results, with an average CE of 99.5% for anode-free Cu||LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cells and an extended lifespan.

“The developed electrolyte shows remarkable improvement in calendar life and cycling stability of Li (50 µm)||NMC811 (4 mAh cm⁻²) cells, maintaining 80% capacity after 568 and 218 cycles at room temperature and 60 °C, respectively,” the researchers wrote. “Furthermore, our 410 Wh kg⁻¹ prototype pouch cells demonstrate 80% capacity retention for 470 cycles.”

The new strategy introduced by this research team could soon inform additional studies, ultimately facilitating the development of new superior liquid electrolytes for high-density Li-metal batteries. Moreover, their work contributes to the understanding of fluorinated ether diluents, highlighting their potential for the development of next-generation battery solutions.

Researchers from the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, have established new, scalable methods of developing battery- and solar-powered fibers, making it theoretically possible for electrical energy to be harvested from, and stored in, the clothing people wear.

These fibers could power high-performance wearable electronics that breathe, stretch and wash just like conventional textiles.

This development in fiber power sources—submillimeter-thin battery and photovoltaic strands that could be woven directly into fabrics—opens up a new world of wearable electronics and smart textiles.

Instead of carrying a heart monitor with bulky batteries, a patient could wear a shirt that has battery- and solar-powered fibers knit into it. Fiber-powered clothing could be heated to keep a person warm in cold environments, or laced with battery- and solar-powered fibers to provide soldiers with hands-free audio and video recording in the field.

“As demands for electronic textiles change, there is a need for smaller power sources that are reusable, durable and stretchable,” said Konstantinos Gerasopoulos, assistant program manager for physics, electronic materials and devices at APL and lead investigator of this project.

“Our vision is to develop solar harvesting fibers that can convert sunlight to electricity and battery fibers that can store the generated electricity in the textile.”

Stretching the limits

Manufacturing and design have limited the scalability and performance of fiber batteries. Industrial textile equipment has been used to manufacture fiber batteries, but its massive scale limits its use to specialized facilities that are not compatible with the battery industry. Standard fiber batteries also suffer from lower performance because the electrodes are commonly twisted together, which renders most of the electrode surface inactive.

Now, in a study published in Advanced Materials Technologies, APL scientists have demonstrated a novel method to scale up fiber battery fabrication.

Rather than using textile equipment, the APL team customized battery equipment to achieve the thinness required for fiber batteries. This strategy, including the creation of customized roll-to-roll setups, made the process portable and suitable for large-scale production. All the equipment needed to create the fiber batteries could fit in a small room.

“We were always designing with roll-to-roll compatibility in mind,” said Rachel Altmaier, the paper’s lead author. “We need to be able to run all of our processes continuously or else what we develop isn’t relevant. This process could be dropped into an existing manufacturing line.”

The batteries are made of flat strips of anode and cathode electrodes and a polymer separator that are fed together into a heated roll press and laminated into a stacked design. The construction is similar to that of conventional pouch cells—think cell phone batteries—and provides stronger power and performance than standard fiber batteries. The stack is then laser-cut into a fiber-like strand roughly 700 micrometers wide—about the width of five human hairs.

This marks the first use of laser cutting on a full battery stack and demonstrates the method’s viability for customizing battery size and maintaining performance. The cutting system’s quickness also makes it scalable.

“We can process 100 meters of total fiber in a little over five hours,” said Jason Tiffany, an engineer at APL and co-author on the paper. “With our process, we can make the fibers smaller and more energy dense, which could open even more opportunities for textile applications.”

The fiber battery work adds to the team’s technology toolbox, which has included the development of a flexible lithium-ion battery that can operate under extreme conditions, as well as safe, fast-charging batteries.

In a second paper also published in Advanced Functional Materials, the APL team also addressed the challenge of making scalable, high-performing fibers that can harvest light and convert it into electricity.

“Just like with the battery fibers, we were inspired by conventional solar cell technology that is very efficient and robust,” said Gerasopoulos. “We asked, how can we turn these power sources into fibers?”

“The biggest challenge with current solar cell technology is its rigidity,” said Michael Jin, lead author of the solar cell paper. “You can imagine shrinking solar panels, like those on a rooftop, into a tiny solar fiber is very challenging.”

To overcome this challenge, the team leveraged a specific type of solar cell that has both positive and negative terminals on the back side in a finger-like pattern. Starting from this cell, the researchers cut and assembled tiny solar cells on thin, flexible circuit boards before sealing them in a protective polymer to create a fiber-like strand. The solar cells are so small they could fit between the ridges of a fingerprint.

“We used standard microelectronics fabrication processes to develop a novel approach that has transformed current rigid solar cell technology into flexible and durable fibers,” Jin said. “Even after bending the fiber 8,000 times, we saw no change in its performance.”

To further test the robustness of these fibers, the team continuously exposed them to light in the lab, simulating the total sunlight hours that Washington Dulles International Airport experiences in a typical spring month. Still, the fiber efficiency remained unchanged.

In a proof of concept, the researchers used a custom-built mini loom to weave nylon and solar cell fibers into a small textile. The swatch of fibers was placed under a lamp and attached to a small circuit board and an LED blinker, and within seconds, the strip powered the blinker’s flashing red light.

The method used to assemble and encapsulate the solar cells onto fiber substrates is also extensible to other sources. Instead of solar cells, it could be sensors, LEDs or batteries mounted onto the surface of flexible fibers, which could generate numerous functionalities.

“Our team continues to look for ways to create the most effective, resilient, cutting-edge power sources,” said Jeff Maranchi, research program area manager in APL’s Research and Exploratory Development Department.

“Textiles that integrate light energy harvesting and battery fibers could revolutionize what wearables today can achieve. Very soon, these fibers will enable distributed fabric-based power, heating, communications and sensing while providing the comfort and ease of regular textiles.”

Did your grandmother also do the laundry when a sunny day was forecast? Now that so many households have solar panels and the electricity network is experiencing problems due to overload at peak times, it would also be better if households with solar panels run appliances such as the washing machine on sunny days. The energy generated is then immediately consumed instead of stored, reducing grid congestion.

However, in practice, people do not always do this. Naomi Hubert investigated why this is the case during her master’s degree at TU Delft.

“Many people with solar panels have difficulty shifting their energy consumption to periods when this energy is produced, while this can actually help reduce blockages on the energy network. Especially now that more and more households are generating energy themselves with their solar panels, and that number is still rising.” Hubert explains.

“In my research, I interviewed 283 Dutch households with solar panels about their ‘washing’ behavior.” Washing behavior is a fairly flexible habit, but it is also relatively energy-intensive.

Routine

The research now published in Energy Research & Social Science, shows that there are various factors that influence whether or not people’s washing time is shifted.

It appears to be difficult for people to adapt to technologies, such as washing when the solar panels provide plenty of energy. This is because households have difficulty monitoring the energy production of their solar panels and the energy consumption of their household.

In addition, doing the laundry has become a routine activity that is often done on a standard day and time. Another point is that people who have difficulty shifting the time they are doing their see themselves as passive users of the energy system. This means that they do not feel like an active participant of the (solar) energy system.

Finally, it emerged that people are not well informed about the benefits of using energy when it is generated, or ways in which they could do so.

Behavioral change supported by technology and information

These results show that technology and behavioral change must support each other, but that this is not self-evident. It is important that we not only look at the individual, but also at the bigger picture. For example, automation of appliances can support changing routine washing behavior, but will probably not be sufficient.

Providing practical information and clarifying that households do play an active role in the energy system is equally important. Hubert says, “The rise of solar panels is a great development for the energy transition, but to prevent problems with overloading the energy network, the behavior of households must also change. People need to be supported in this change. I hope to contribute to that with this research.”

Lithium-ion batteries are widely used in new energy vehicles due to their low self-discharge rate and long cycle life. Currently, the anode material of commercial lithium-ion batteries mainly adopts graphite, with a theoretical capacity of only 372 mAh g-1—which has gradually failed to meet the increasing demand for energy density.

Silicon has been widely studied by virtue of its high theoretical capacity of 4,200 mAh g-1. However, silicon produces volume changes of up to 300% during lithiation and delithiation, and the ensuing mechanical degradation and capacity loss hinder applications.

To reduce the adverse effects caused by mechanical deformation, silicon structure optimization has been intensively investigated and has effectively improved the cycling performance. Nonetheless, the long-term development of silicon-based energy storage materials requires not only stable electrodes, but also a stable interphase between electrodes and electrolytes.

Organic electrolytes, which are widely used in conventional lithium-ion batteries, reduce on the anode surface to form a thin film called solid electrolyte interphase (SEI).

Unfortunately, drastic volume changes in silicon can lead to the accumulation of stress and destruction of the SEI, which will subsequently regenerate on the exposed anode surface, greatly increasing irreversible lithium and electrolyte consumption and causing capacity degradation. Therefore, it is particularly important to stabilize the mechanical properties of SEI on silicon materials.

To that end, the Advanced Power Research Group led by Peng Tan of the University of Science and Technology of China (USTC) has initiated a modeling study on the mechanical stability of SEI from three perspectives: electrode material properties, SEI geometrical properties, and battery operating conditions. The work has been published in Advanced Powder Materials.

The modeling was based on the continuum mechanics model, coupled with the electrochemical mass transfer process.

The team quantitatively analyzed the effects of three factors on SEI stability and battery capacity utilization by building a model of individual electrode particles.

They found out that in order to improve SEI stability, spherical silicons with smaller particle sizes should be used as much as possible in the design of electrode materials. In terms of SEI geometry, it is particularly important to artificially construct SEI with a uniform structure, while when it comes to cell operation, high multiplicity will bring greater capacity utilization but is not conducive to SEI stability.

The findings demonstrate SEI’s high-stability design and operation strategy and will guide the development of silicon-based energy storage batteries with high cycling stability.