X-ray study redefines role of battery material from cathode to catalyst

PICTURE

PICTURE: Wanli Yang, principal investigator at the Advanced Light Source at the Berkeley Lab, is working on a resonant inelastic x-ray scattering system (RIXS). Yang adapted the RIXS technique for a recent Joule study … see After

Credit: Berkeley Lab

An international team working at the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) used a unique x-ray instrument to learn new things about lithium-rich battery materials that have been the subject of many studies for their potential to expand the range. electric vehicles and the operation of electronic devices.

The researchers focused their research on a material called lithium manganese oxide (Li2MnO3), the extreme example of so-called “lithium-rich” materials, containing as much lithium as possible in this family of materials. A newly developed principle of the battery community is that battery electrodes made of materials rich in lithium could provide high voltage, high capacity operation because the oxygen in the material participates in reversible “redox” chemical reactions, in which oxygen atoms lose and lose cyclically. gain electrons, which allows the battery to have a greater capacity for storing and using the electric charge.

However, this work has shown that the reversible reactions do not actually involve oxygen in the Li2MnO3 during battery operation. Instead, a closer analysis of the other element of the material, manganese, revealed that the reason the material could be recycled was due to an unusual and complete switch to manganese-based reactions, with a relatively low capacity, just after the first charge. This discovery paves the way for exploration of high-energy electrode materials outside of the lithium-rich family.

In addition, the research team was particularly surprised to observe a “partially reversible” formation and disappearance of carbonate compounds on the surface of the material. These highly reactive surface properties suggest that the material can function as a catalyst and could facilitate the reversible chemical reactions required for next-generation exotic batteries like lithium-air and lithium-carbon dioxide batteries. The carbonate compounds seen on the surface of Li2MnO3 contain carbon bound to oxygen atoms, meaning that lithium-rich materials could be effective catalysts for reactions involving carbon dioxide gas.

“What we all think is exciting is that, through a fundamental spectroscopic study of this material, we have not only clarified the reaction mechanism of this much debated material, but also found a conceptually different use for it. as a catalyst, ”said Wanli Yang, senior researcher at the Advanced Light Source (ALS) at the Berkeley Lab who adapted a technique called resonant inelastic x-ray scattering (RIXS) for this type of battery study. He was also a co-author of the study, working within the framework of a large international collaboration. The study was published on March 4 in the journal Joule.

“Some findings have indicated that this material is in fact more suitable as a catalyst because of its highly reactive surface. Thus, our collaborators in the field of battery materials tested it as a catalyst and found that it indeed had superior performance for lithium carbon dioxide and lithium air batteries “. he added.

The researchers noted in the study that the high capacity carbonate cycle based on the Li2MnO3 catalyst has superior reversibility compared to similar systems with typical oxide catalysts. The results also open the door to a whole class of alkali-rich materials to use as catalysts for other applications, such as fuel cells.

Key to the study was a specialized beamline at ALS that can essentially dissect chemical reactions one element at a time to find out which are – or are not – involved in the reactions. The ALS is a synchrotron that can produce light in a range of “colors” or wavelengths, from infrared to x-rays.

The researchers used RIXS to map the chemistry of samples at different stages of the charge-discharge cycle. They found no evidence of the reversible redox reactions expected for this material by many scientists. Instead, they found that oxygen was only involved in a one-way oxidation reaction and very active surface reactions.

Yang noted that the study reverses several popular models for understanding redox activities in battery electrodes, but opens up new thinking about low-cost types of materials that can use redox reactions, as the researchers have found that the behavior of the oxidation-reduction reaction of oxygen in lithium-rich electrodes is in fact the same as that of conventional electrodes in use today. Taking advantage of the oxidation-reduction reaction of oxygen could potentially allow batteries to exhibit high voltage and high capacity performance.

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Other scientists from the Berkeley Lab also participated in the research; SLAC National Accelerator Laboratory; Stanford University; and Peking University Shenzhen Graduate School, Tianjin Normal University, Northeast University and Chinese Academy of Sciences in China.

The work was supported by the United States Department of Energy (DOE) Office of Science, the United States DOE’s Data, Artificial Intelligence and Machine Learning Project at DOE Science User Facilities, the National Key R&D Program of China, Beijing Municipal Science & Technology Commission, and the National Foundation of Natural Sciences of China, and the work of Stanford University was supported by the US Bureau of Basic Energy Sciences, Division of Materials Science and engineering.

The Advanced Light Source is a user installation from the DOE Office of Science at the Berkeley Lab.

Founded in 1931 on the belief that the greatest scientific challenges are best met by teams, the Lawrence Berkeley National Laboratory and its scientists have received 14 Nobel Prizes. Today, researchers at the Berkeley Lab are developing sustainable energy and environmental solutions, creating useful new materials, advancing the frontiers of computing, and exploring the mysteries of life, matter, and the universe. Scientists around the world rely on the lab’s facilities for their own science of discovery. Berkeley Lab is a national, multiprogrammed laboratory, operated by the University of California for the Office of Science of the US Department of Energy.

The DOE Office of Science is the biggest proponent of basic physical science research in the United States and works to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.

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