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October 2012

Better Safe than Sorry

Highly customizable polymer microspheres effectively prevent battery operation at dangerous temperatures

Lynn Trahey

Scanning electron micrograph showing cross-section of battery anode (mid-region) with polyethylene spheres above. Solid gray band at bottom of image is the copper current collector.

The safety aspects of lithium-ion batteries – will my laptop, car, or iPhone catch fire? – are worthy to ponder in this day of lithium-ion battery popularity. The production and use of lithium-ion batteries for consumer electronics and the transportation sector, in particular, are on a significant rise thanks to their attractively high energy density. Although instances of these batteries catching fire are rare, they can happen, and for this reason scientists are researching fail-proof ways to shut down batteries in the presence of dangerous triggers.

Thermal management within lithium-ion batteries is critical. The individual cells, ranging from one to hundreds in a battery depending on the application, contain the necessary ingredients for a fire – a combustible electrolyte in proximity to an oxidant and reductant. A separator physically prevents the anode (negative electrode) and cathode (positive electrode) from touching and internally short-circuiting the cell. The separator also must house the electrolyte for lithium-ion transport. An additional functionality of the separator is to melt and "shut down" the battery by stopping current flow completely in the event of an abnormal temperature increase, which can lead to fire. Although traditional polyethylene-based separators melt at about 135 oC, successful shutdown is not guaranteed.

Researchers at the Center for Electrical Energy Storage (CEES): Tailored Interfaces are developing a cell additive that melts and halts all ion and electron transport within batteries. "The research is targeted to make lithium-ion batteries safer for the general public," says Scott White, professor of Aerospace Engineering at the University of Illinois, Urbana-Champaign and CEES lead researcher. "It's also a cool example of a development in one field being applied to another field. Original 'self-healing,' capsule-based research was supported by the Department of Defense and here we're transitioning and using the same concepts in Department of Energy battery research."

In their article, which appeared in the May 2012 issue of Advanced Energy Materials (with cover page), a team of CEES researchers described the synthesis of polyethylene and paraffin wax microspheres and their functionality. The addition of a small amount of microspheres did not impede the cell's normal performance at moderate temperatures. However, when the temperature of a cell was raised (110 oC for polyethylene, 65 oC for paraffin), the microspheres melted and effectively shut down cell operation, preventing thermal runaway.

Based on this success and borrowing from a background in "smart" materials research, scientists in CEES are looking for ways to shut down batteries using various triggers, such as cell voltage, resistance change, current flow, or reduction/oxidation event. "I'm excited about the possibilities for microcapsules," says Marta Baginska, a graduate student working with CEES and lead author of the Advanced Energy Materials paper. "With thermoresponsive microcapsule incorporation, we have proof–of-concept that microcapsules can function usefully in lithium-ion batteries. Now we can think about multifunctionality."

Acknowledgments

This research was supported as part of the Center for Electrical Energy Storage, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Office of Basic Energy Sciences. M Baginska would also like to acknowledge the American Association of University Women for its Selected Professions fellowship and the University of Illinois Urbana-Champaign College of Engineering for its SURGE fellowship.

More Information

Baginska M, BJ Blaiszik, RJ Merriman, NR Sottos, JS Moore, and SR White. 2012. “Autonomic Shutdown of Lithium-Ion Batteries Using Thermoresponsive Microspheres." Advanced Energy Materials 2:583-590. DOI: 10.1002/aenm.201100683

About the author(s):

  • Lynn Trahey received her Ph.D. in Chemistry from the University of California at Berkeley in 2007 studying thermoelectric materials and nanoporous templates. She currently works in the Electrochemical Energy Storage Department at Argonne National Laboratory, and is a member of the Center for Electrical Energy Storage EFRC and the Joint Center for Energy Storage Research. Her research interests include electrodeposition and the design and characterization of energy-relevant materials.

The Safety Is in the Spheres

Tiny polyethylene beads melt and prevent lithium-ion batteries from catching fire

Tiny polyethylene spheres added to a lithium-ion battery melt when the battery’s internal temperature rises and shut down the battery, preventing any chance of runaway combustion.

Used in laptop computers and other devices, lithium-ion batteries can overheat and catch fire. Although thin separators inside the batteries melt when the internal temperature reaches about 135 oC, successful shutdown is not guaranteed. Scientists tried a new approach, adding different coatings inside the battery. A coating of tiny polyethylene spheres shut the battery down at 110 oC. A paraffin wax sphere coating stopped the action at 65 oC. In both cases, the material did not interfere with the battery’s operation at moderate temperatures. One day, these materials could reliably prevent fires and help result in further, more large-scale use of lithium-ion batteries. The Center for Electrical Energy Storage: Tailored Interfaces, led by Argonne National Laboratory, performed this research.

More Information

Baginska M, BJ Blaiszik, RJ Merriman, NR Sottos, JS Moore, and SR White. 2012. “Autonomic Shutdown of Lithium-Ion Batteries Using Thermoresponsive Microspheres." Advanced Energy Materials 2:583-590. DOI: 10.1002/aenm.201100683

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.