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January 2013

Prying into the Workings of Lithium-Ion Batteries

New techniques capture nanoscale reactions in real time

Jianguo Yu

Intra-particle and inter-particle flow can now be tracked in electrodes thanks to an in situ cell constructed for a transmission electron microscope.

Scientists at the Northeastern Center for Chemical Energy Storage have developed novel techniques to track the kinetics of lithium ions in batteries. With these new techniques, the team tracked the transport of lithium ions and exposed subtle changes in the nanoparticles that occurred in the batteries' electrodes over time, with nanoscale (billionths of a meter) precision. By combining the real-time direct observation with computation, this study — published in Nature Communications — contributes to a better understanding of how electrodes function in these crucial materials and paves the way to develop improved lithium-ion batteries, which are essential in our daily life.

"We've opened a fundamentally new window into this popular technology," said lead author Feng Wang, a physicist at Brookhaven National Lab. "The live, nanoscale imaging may help pave the way for developing longer-lasting, higher-capacity lithium-ion batteries. That means better consumer electronics, and the potential for large-scale, emission-free energy storage."

Development of high-energy storage devices is vital to help diversify our energy resources and reduce our dependency on fossil fuels. Rechargeable lithium-ion batteries have dominated the market of storage systems because of their high energy density. However, these dense and lightweight energy storage devices begin to degrade over time, limiting their applications in powering electric vehicles or facilitating grid-scale energy storage, which demand battery lifetimes longer than a decade.

To develop new electrodes for lithium-ion batteries of greater energy and power densities along with a substantial increase in both calendar and cycle life, scientists require an improved understanding of the mechanisms for lithium-ion transport and the reactions involved at the active components of a working device at an atomistic level. Thus, it is imperative to have an atomistic-level understanding and to circumvent the electrode kinetic issues by tracking physical and chemical changes of active components in a working electrode. 

In this study, the electrochemical lithiation of single nanoparticles was investigated with unprecedented spatial resolution and analytical capability. Lithiation is a reaction in which lithium ions move from the negative electrode to the positive electrode during discharge. Specifically, the scientists custom-built an electrochemical cell to operate inside a transmission electron microscope. The team observed the lithium reaction process as it unfolded across iron fluoride nanoparticles. Such nanosized electrode materials were chosen for the study because they have significantly higher lithium capacity than conventional electrodes.  

These real-time experimental observations, supported by advanced computation, revealed that the lithium ions swept rapidly across the surface of the nanoparticles in a matter of seconds. The transformation then moved slowly through the bulk in a layer-by-layer process that split the compounds into distinct regions. Such a morphological evolution resembles spinodal decomposition, a mechanism by which a solution having two or more components can separate into distinct regions with distinctly chemical compositions and physical properties. This new mechanism may help to pave the way to develop high-energy conversion electrodes for lithium-ion batteries.

More Information

Wang F, HC Yu, MH Chen, L Wu, N Pereira, K Thornton, A Van der Ven, Y Zhu, G Amatucci and J Graetz. 2012. "Tracking Lithium Transport and Electrochemical Reactions in Nanoparticles." Nature Communications 3:1201. DOI: 10.1038/ncomms2185

Acknowledgments

The research was supported by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center led by Stony Brook University and funded primarily by the Department of Energy's Office of Science, Office of Basic Energy Sciences. Some of the facilities used were supported by the Center for Functional Nanomaterials at Brookhaven National Lab, and by the National Science Foundation at Michigan.

About the author(s):

  • A member of the Center for Materials Science of Nuclear Fuel, an Energy Frontier Research Center, Jianguo Yu is a staff scientist at Idaho National Laboratory. He's developing simulation methodologies to bridge atomistic methods and mesoscale models in a self-consistent manner for nuclear fuels and cladding materials.  He's also studying electron and ion transport in lithium-/sodium-ion rechargeable batteries. 

Tracking Lithium Down

New method provides exquisite, real-time living images of ions in battery electrode at nanoscale

A drawing showing the propagation of reaction front through a single FeF2 particle via a layer-by-layer process.

Batteries that last a decade or more to store and release energies generated by sources such as wind turbines or solar farms are vital to reducing our fossil fuel dependency. Could rechargeable lithium-ion batteries be improved to step up to this challenge and become a sustainable technology for the future? Replacing today's electrodes with lithium conversion compounds could theoretically boost the battery's capacity. To understand the implications of such a change and to circumvent the electrode kinetic issues, scientists built a device that brings the power of a transmission electron microscope to bear on the material. Previous methods could not provide this level of scrutiny. This new device provides real-time kinetics of the lithium ion with extreme resolution, generating images on the same scale used to measure atoms. This device, which has already generated new data on lithium's movement and reactions inside the conversion materials, could open new doors to designing materials for next generation energy storage. Scientists at the Northeastern Center for Chemical Energy Storage, led by Stony Brook University, completed the research.

More Information

Wang F, HC Yu, MH Chen, L Wu, N Pereira, K Thornton, A Van der Ven, Y Zhu, G Amatucci and J Graetz. 2012. "Tracking Lithium Transport and Electrochemical Reactions in Nanoparticles." Nature Communications 3:1201. DOI: 10.1038/ncomms2185

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.