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November 2014

Make Way for Lithium! En Route to More Efficient Batteries

Computational modeling of battery reactions points to more efficient energy storage

Nicholas Quackenbush

Results of the phase field simulations showing the lithium concentration (light green) entering the Cu0.5TiS2 electrode particle during discharge (top) and exiting during charge (bottom), demonstrating the difference in reaction pathways. Reproduced with permission (modifed from article) of The Royal Society of Chemistry.

At the NorthEast Center for Chemical Energy Storage (NECCES), researchers are exploring new avenues for rechargeable lithium-ion battery chemistry, and the results point the way to more efficient energy storage. Using a novel computational approach that examined reactions at multiple time and length scales, the group identified fundamental factors that determine the reaction pathways taken during battery charging and discharging. The disparity between the charging and discharging reactions is thought to be a major cause of a phenomenon, called hysteresis, which ultimately results in unacceptable energy loss.

As the demand for higher capacity lithium-ion batteries for applications such as mobile electronics or electric vehicles continually grows, new battery chemistries are being sought out. Current industrial batteries rely on intercalation processes in the cathode, which require a host material that readily incorporates lithium with minimal changes to its structural framework. To overcome the capacity limitations inherent to these cathodes, other reaction mechanisms are being considered, including conversion and displacement reactions. In the displacement reaction process, the host framework is retained just as in intercalation reactions, although as the lithium is inserted, there is a concomitant extrusion and/or precipitation of another metal from the cathode. This opens up more possible lithium sites, meaning more energy storage.

The team chose a material made from copper, titanium, and sulfur atoms, Cu0.5TiS2, as their model system because it is known to display the undesirable hysteresis in the voltage curve when used in a battery. Computer modeling of the material started with a view at the atomic level. The team investigated which sites the lithium and copper ions prefer and how each would migrate from site to site within the titanium and sulfur, TiS2, framework. Using computer simulations, specifically kinetic Monte Carlo simulations that provided key input to phase field simulations, the team scaled up their results to length and time scales relevant for the charging and discharging of a cathode particle as in a rechargeable battery.

The results of these simulations provide a comprehensive description of the disparate charging and discharging reaction pathways that underlie the observed hysteresis. For the discharge simulation, the lithium insertion required a simultaneous expulsion of the copper to the surface of the electrode particle. The charging simulations, however, showed that the rate of the copper returning into the particle greatly lagged that of the lithium moving out. The lag is a result of the copper having a much lower mobility than the lithium and a lack of "drive" for the reinsertion reaction. Because of this, much more electrical work must be put into the battery than can later be used to power a device.

Through their calculations, the team points out that this problem can be substantially reduced by carefully choosing future cathode materials. The research could lead to streamlining the process of searching for new materials by identifying the atomic-scale metrics that will minimize the energy wasting hysteresis. This pioneering study across multiple scales is relevant to any displacement reaction and has pointed the way toward energy-efficient high-capacity rechargeable batteries.

Acknowledgments

This work was supported by the NorthEast Center for Chemical Energy Storage, an Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The phase field simulations and first-principles calculations were performed using computational resources provided on the Extreme Science and Engineering Discovery Environment, which is supported by the National Science Foundation.

More Information

Yu HC, C Ling, J Bhattacharya, JC Thomas, K Thornton, and A Van der Ven. 2014. “Designing the Next Generation High Capacity Battery Electrodes.” Energy and Environmental Science 7:1760-1768. DOI: 10.1039/C3EE43154A

About the author(s):

  • Nicholas Quackenbush is a Ph.D. candidate studying physics under the advisement of Louis Piper at Binghamton University. Nicholas is a member of the NorthEast Center for Chemical Energy Storage (NECCES). His research focuses on using synchrotron X-ray spectroscopic techniques to investigate materials for lithium-ion battery cathodes and other smart energy devices.

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Designer materials inspire charging and discharging reactions in high-capacity batteries

When charging displacement batteries, the copper ions do not return to the electrode as fast as the lithium ions leave, meaning that more electrical work must be put into the battery than can be retrieved.

As any cell phone user knows, the longer a lithium-ion battery can go between charges, the better. Newer batteries that store more energy use a displacement process—when lithium enters the electrode, copper exits. Sadly, these batteries suffer from poor efficiency, meaning that much more energy needs to be put into the battery than can be used later. The culprit is hysteresis, a lag between adding or removing energy and the associated chemical reactions. Using computational simulations, the team at the NorthEast Center for Chemical Energy Storage, led by Binghamton University, examined the displacement process from the atomic scale to a fully functioning battery. They identified the reactions responsible for hysteresis. They also determined the properties the electrode needs to avoid this troubling phenomenon. Their work could lead to more effective batteries for electric vehicles and other uses.

More Information

Yu HC, C Ling, J Bhattacharya, JC Thomas, K Thornton, and A Van der Ven. 2014. “Designing the Next Generation High Capacity Battery Electrodes.” Energy and Environmental Science 7:1760-1768. DOI: 10.1039/C3EE43154A

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.