Batteries have come a long way since Volta first stacked copper and zinc discs 200 years ago. As technology has continued to evolve from lead-acid to lithium-ion, many challenges remain, such as achieving higher density and suppressing dendrite growth. Experts are rushing to meet the growing global need for energy efficient and safe batteries.
The electrification of heavy goods vehicles and planes requires batteries with higher energy density. A team of researchers believe a paradigm shift is needed to have a significant impact on battery technology for these industries. This change would take advantage of the anionic reduction-oxidation mechanism in lithium-rich cathodes. The findings published in Nature marks the first direct observation of this anionic redox reaction in a lithium-rich battery material.
Collaborating institutions included Carnegie Mellon University, Northeastern University, Lappeenranta-Lahti University of Technology (LUT) in Finland and institutions in Japan including Gunma University, Japan Synchrotron Radiation Research Institute (JASRI) , Yokohama National University, Kyoto University and Ritsumeikan University.
Lithium-rich oxides are promising cathode material classes because they have been shown to have a much higher storage capacity. But, there is an “ET problem” that the materials in the battery must satisfy: the material must be able to charge quickly, be stable in extreme temperatures, and cycle reliably for thousands of cycles. Scientists need to clearly understand how these oxides work at the atomic level and how their underlying electrochemical mechanisms play a role in solving this problem.
Normal Li-ion batteries operate by cationic redox, when a metal ion changes oxidation state when lithium is inserted or removed. In this insertion frame, only one lithium-ion can be stored per metal-ion. Lithium-rich cathodes, however, can store much more. Researchers attribute this to the anionic redox mechanism – in this case, oxygen redox. This is the mechanism credited with the large capacity of the materials, almost doubling the energy storage compared to conventional cathodes. Although this redox mechanism has become the main competitor among battery technologies, it represents a pivot in materials chemistry research.
The team set out to provide conclusive evidence for the redox mechanism using Compton scattering, the phenomenon by which a photon deviates from a straight path after interacting with a particle (usually an electron). Researchers performed sophisticated theoretical and experimental studies at SPring-8, the world’s largest third-generation synchrotron radiation facility, operated by JASRI.
Synchrotron radiation consists of the narrow and powerful beams of electromagnetic radiation that are produced when the electron beams are accelerated to (almost) the speed of light and are forced to travel in a curved path by a magnetic field. Compton scattering becomes visible.
The researchers observed how the electron orbital that lies at the heart of reversible and stable anionic redox activity can be imaged and visualized, and its character and symmetry determined. This first scientist can be a game-changer for future battery technology.
Although previous research has offered alternative explanations for the anionic redox mechanism, it could not provide a clear picture of the quantum mechanical electronic orbitals associated with redox reactions because this cannot be measured by standard experiments.
The research team had an “A ha!” when they first saw the redox agreement between theory and experimental results. “We realized that our analysis could image the oxygen states that are responsible for the redox mechanism, which is something fundamentally important for battery research,” said Hasnain Hafiz, lead author of the study who carried out this work during his postdoctoral research time. partner at Carnegie Mellon.
“We have conclusive evidence to support the anionic redox mechanism in a lithium-rich battery material,” said Venkat Viswanathan, associate professor of mechanical engineering at Carnegie Mellon. “Our study provides a clear picture of how a lithium-rich battery works at the atomic scale and suggests avenues for the design of next-generation cathodes to enable electric aviation. The design of high energy density cathodes represents the next frontier for batteries. “
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Material provided by College of Engineering, Carnegie Mellon University. Original written by Lisa Kulick. Note: Content can be changed for style and length.