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April 2012

Diving into Lithium-Ion Batteries

Why do batteries degrade after only a few hundred cycles?

Scott Kirklin

Schematic of the SICM. The current passing through the micropipette is measured as it scans across the surface of the electrode.

The full answer to that question may be a step closer, based on new developments in a technique known as scanning ion conductance microscopy, or SICM, by researchers at the Center for Electrical Energy Storage. Albert Lipson, a graduate student with the Center at Northwestern University, has adapted a technique used previously in the biological sciences for characterizing cellular structures to improve our understanding of how and why batteries fail.

Each electrochemical cell of a lithium-ion battery is basically a sandwich consisting of two electrodes: the anode, typically graphite, and the cathode, typically a lithium-metal-oxide, such as LiCoO2. The electrodes are separated by a lithium-ion-conducting electrolyte. When the cell is charged, lithium is extracted from the cathode and transported through the electrolyte to the anode. The reverse process occurs during discharge: lithium ions move from the anode to the cathode. While the lithium ions move through the electrolyte, electrons are transported through an external circuit to run your cell phone or the motor of an electric car. If any of these processes are seriously interrupted, the battery fails.

With the SICM technique, an extremely fine-tipped pipette, about 100 nanometers in cross section, is used to scan the electrode surface in a liquid electrolyte bath. As the pipette moves across the surface, it measures the flow of ions through the tip. Based on the measured flow, only a few picoamperes in magnitude, the reactivity of the electrode can be mapped. Simultaneously, local changes in height can be measured and when coupled with the reactivity map, these changes can give an in-depth understanding of how the battery electrodes operate during cycling.

Because SICM can monitor chemical activity and local topology, it is well-suited for studying failure mechanisms in lithium-ion batteries, particularly at electrode surfaces where damaging effects can occur. In a recent paper by Lipson and his colleagues, they report that the SICM technique can measure extremely small currents at a spatial resolution down to hundreds of nanometers. For comparison, viruses are measured on the same scale.

By investigating chemical reactions at the nanoscale, the researchers are improving their understanding of how and where irreversible side reactions, cracking and other degradation mechanisms occur. Although nascent, the technique shows promise for elucidating how and why batteries operate the way they do.

Acknowledgments

The Center for Electrical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences supported this research. RSG and the SICM instrument were funded by the Army Research Office. Battery testing instrumentation was funded by the Initiative for Sustainability and Energy at Northwestern.

More Information

Lipson AL, RS Ginder and MC Hersam. 2011. “Nanoscale In Situ Characterization of Li-ion Battery Electrochemistry via Scanning Ion Conductance Microscopy.”  Advanced Materials 23(47):5613-5617. DOI: 10.1002/adma.201103094

About the author(s):

  • Scott Kirklin is a Ph.D. candidate in Christopher Wolverton’s research group at Northwestern University, and a member of the Center for Electrical Energy Storage, an Energy Frontier Research Center. His research is focused on using high-throughput first-principles methods to facilitate materials discovery for energy applications.

Taking Biology to Batteries

Used to study delicate cells, microscope repurposed to examine energy storage materials

Cover of Advanced Materials. Copyright: John Wiley and Sons. AL AL, RS Ginder, and MC Hersam. 2011. “Nanoscale In Situ Characterization of Li-ion Battery Electrochemistry via Scanning Ion Conductance Microscopy.” Advanced Materials 23(47):5613-5617. DOI: 10.1002/adma.201103094

If you use a cell phone or laptop computer, you know lithium-ion batteries degrade far too quickly. This degradation limits the use of such batteries in hybrid electric vehicles and other larger applications. If the undesirable reactions that degrade the battery’s performance are understood, scientists can design longer-lasting batteries. Part of the challenge in tracking down the reactions is seeing what happens on the surface. Scientists took the scanning ion conductance microscope, an entirely no-contact method used by biologists, and altered it. The revised microscope provides images with a resolution on the scale of hundreds of nanometers. It also measures the local ion current. While this technique is in its infancy, it can provide scientists with nanoscale data about undesirable reactions and ultimately enable the next generation of batteries. This work was done by the Center for Electrical Energy Storage, led by Argonne National Laboratory.

Written by Scott Kirklin and Kristin Manke

More Information

Lipson AL, RS Ginder and MC Hersam. 2011. “Nanoscale In Situ Characterization of Li-ion Battery Electrochemistry via Scanning Ion Conductance Microscopy.”  Advanced Materials 23(47):5613-5617. DOI: 10.1002/adma.201103094

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.