New cobalt-free lithium-ion battery cathode offers higher stability.
Newswise — The batteries that power our cell phones, laptops and electric vehicles all have one major drawback: They all rely on cobalt. Cobalt is a hard-to-find metal that is largely drawn from poorly regulated African mines. This mining is problematic for the environment, as well as for miners, and it can also lead to broader exploitation in countries where it is mined.
In order to find other solutions for batteries">lithium-ion batteries that move away from a dependency on cobalt, researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have participated in a collaborative study to identify new potential materials for the positive terminal of a battery, called a cathode. In a battery, lithium ions are inserted into a cathode during charging and released during discharging, providing electricity.
The new cathodes offer two advantages: They are both cobalt-free and stable, which means that they do not undergo a structural failure, such as cracking, as they are repeatedly charged and discharged.
As a battery constituent, cobalt offers thermal stability, which means it functions even as it is heated to higher temperatures, as well as structural stability. Researchers have been looking for different materials that could offer these same advantages without cobalt’s flaws.
In the new study, a research team led by the University of California, Irvine created and analyzed a material for a lithium-ion cathode that uses no cobalt and is instead rich in nickel. This cathode chemistry is compositionally complex, meaning that it contains small amounts of a wide range of other metals. These metals include molybdenum, niobium and titanium.
The research team used the resources of the Advanced Photon Source (APS), a DOE Office of Science user facility at DOE’s Argonne National Laboratory. A paper based on the study appeared in the September 21 issue of Nature.
“You can think of building a cathode like building a house out of different kinds of bricks,” said Argonne physicist Wenqian Xu, a co-author on the paper. “By having a variety of different shapes and sizes of bricks, we can enhance the stability of the house. Multiple elements help to ensure the integrity of the cathode particles.”
The researchers wanted to investigate the structural and thermal stability of the new cathode. Other nickel-rich cathodes typically have poor heat tolerance, which can lead to oxidization of battery materials and thermal runaway, which could in some cases lead to explosions. Additionally, even though high-nickel cathodes can accommodate larger capacities, large changes in volume from repeated expansion and contraction can result in poor stability and safety concerns.
To test the new battery, the researchers cycled it more than a thousand times. They discovered that in the process, the cathode material underwent less than 0.5% of volume expansion. This is roughly a tenth of the volume expansion experienced by previous nickel-rich cathodes, which all had stability problems to varying degrees.
“Keeping the volume of the cathode consistent is essential for ensuring its stability,” said Argonne physicist Tianyi Li, a co-author on the paper.
To characterize the heat tolerance of the new cathode material, called HE-LMNO, the UC Irvine team used beamline 11-ID-C at the APS, with the support of Xu and Li, to examine what would happen to the material at high temperatures. As opposed to previous high-nickel cathodes, which showed severe nanocracking at high temperatures, the HE-LMNO undergoes a phase change that allows it to continue to perform and retain capacity. The HE in HE-LMNO stands for high-entropy, a characteristic that refers to the large number of different elements included in the alloy.
“The APS significantly advanced our understanding of the high-entropy doped material we studied,” said UC Irvine’s Huolin Xin, the lead author of the study. “Our results suggest the high-entropy effect is transferable to a broader class of compounds that could form the basis of new battery materials.”
According to Xu, the research could provide design rules for a host of new battery cathodes that could help reduce next-generation lithium-ion batteries’ reliance on cobalt. “We haven’t just found one new battery,” he said. “Really, by mixing different transition metals in the structure, we could potentially see many more interesting cathode candidates. There will potentially be some even better than we have already found.”
To create electrodes for the experiment, the researchers used Argonne’s Cell Analysis, Modeling and Prototyping (CAMP) Facility. “We collaborate with researchers spanning national labs, industry and academia by fabricating electrodes using commercial and novel materials. Our approach enables us to provide baseline electrodes and to validate promising chemistries using pilot scale equipment, which is critical for assessing advanced materials,” said Argonne battery scientist Steve Trask.
About the Advanced Photon Source
The U. S. Department of Energy Office of Science’s Advanced Photon Source (APS) at Argonne National Laboratory is one of the world’s most productive X-ray light source facilities. The APS provides high-brightness X-ray beams to a diverse community of researchers in materials science, chemistry, condensed matter physics, the life and environmental sciences, and applied research. These X-rays are ideally suited for explorations of materials and biological structures; elemental distribution; chemical, magnetic, electronic states; and a wide range of technologically important engineering systems from batteries to fuel injector sprays, all of which are the foundations of our nation’s economic, technological, and physical well-being. Each year, more than 5,000 researchers use the APS to produce over 2,000 publications detailing impactful discoveries, and solve more vital biological protein structures than users of any other X-ray light source research facility. APS scientists and engineers innovate technology that is at the heart of advancing accelerator and light-source operations. This includes the insertion devices that produce extreme-brightness X-rays prized by researchers, lenses that focus the X-rays down to a few nanometers, instrumentation that maximizes the way the X-rays interact with samples being studied, and software that gathers and manages the massive quantity of data resulting from discovery research at the APS.
This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.
The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.
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