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Winter 2019

What Stress Means for Batteries

Researchers develop a technique to study big stress in batteries before they burst

David M. Stewart

Future batteries will likely be made from a few components that are hard and packed very tightly. Unlike modern batteries, which use plastic polymers, these stiff materials may fracture due to the volume expansion of the battery electrodes. Credit: David Stewart, NEES EFRC

During operation, the internal parts of a rechargeable battery can experience high levels of stress as ions are moved between the anode and cathode within it. This pushing and pulling of charge inside the battery causes the anode and cathode to alternately swell and contract, and in part, leads to battery failure. Researchers in the Nanostructures for Electrical Energy Storage (NEES) Energy Frontier Research Center wanted to study how this compressive stress affects the battery, to identify the signs of failure before the battery actually breaks. To achieve this, they developed a new technique called pascalammetry that allowed them to carefully build and monitor a microbattery under stress.

In the pursuit of higher capacity rechargeable batteries, scientists have investigated an enormous number of new anode and cathode materials that store energy. While there are many desirable properties for battery materials, a critical one is the amount that the volume of the material changes due to the insertion or removal of lithium during charge or discharge.

All energy storage materials expand somewhat, but the ones that can store the most energy typically have very large volume expansions, upwards of 300 percent for silicon, one of the highest capacity materials known. Within the confined space of a battery casing, this incredible change in volume will push against the adjacent materials and may cause them to crack or weaken over time. This is especially damaging to the electrolyte, which sits between the anode and cathode and is responsible for preventing short circuits in the battery.

With this in mind, researchers at NEES began by devising a technique that could accurately measure minute changes in the electrical properties of battery materials. They tested their newly developed pascalammetry by placing a microneedle covered in lithium and lithium oxide (the anode and electrolyte, respectively) in contact with a thin film of silicon (the cathode). This setup yields a simple microbattery.


When a battery is being charged, ions flow between atoms in the electrolyte. If the electrolyte is compressed, the atoms move into different positions, which opens additional pathways for ions to flow through the battery. Credit: David Stewart, NEES EFRC

When they first applied a voltage to this microbattery, a small current flowed through it until it was charged to the correct voltage and then the current stopped itself. The team observed that by pressing the needle further into the cathode and compressing it, more current would begin flowing through the already charged battery. If the pressure is released, the current stops, but it restarts every time the battery is compressed. Their conclusion was that the compressive stress was temporarily creating extra pathways and releasing more ions to flow through the electrolyte.

The pascalammetry developed at NEES provides a precise means of measuring this stress-related current and allowed them to calculate how stress from the expanding cathode affects the flow of ions through the electrolyte. With these new measurements, the team explained this phenomenon by expanding upon pre-existing equations that were proposed in the 1980s.

Research into new battery technologies is trending towards the use of materials that are much stiffer than current options, which could lead to more chances for batteries to be damaged by volume expansion. With this new technique and associated equations, battery engineers have a concrete way to identify the signs of high stress in their batteries, which could lead to new designs that can prevent this kind of battery failure. In addition, this will enable researchers to predict in advance how different materials will behave when placed in a real battery, where stress can come from a variety of sources.

More Information

Larson JM, E Gillette, K Burson, Y Wang, SB Lee, and JE Reutt-Robey. 2018. “Pascalammetry with Operando Microbattery Probes: Sensing High Stress in Solid-State Batteries.” Science Advances 4(6):eaas8927. DOI: 10.1126/sciadv.aas8927

Acknowledgments

The work was supported by the Nanostructures for Electrical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.

About the author(s):

  • David M. Stewart is a postdoctoral fellow at the University of Maryland, where he works on new battery materials and nanostructures for improved battery performance as part of Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center.

How to Measure Stress (for batteries, that is)

New technique probes electrode swelling and shrinkage

Researchers devised a way to measure a battery’s internal stress, potentially leading to a better understanding of how to prevent batteries from bursting. Credit: Nathan Johnson, Pacific Northwest National Laboratory

While most people feel occasional stress in the office, batteries are stressed every time they work. That stress comes from the electrodes, which can expand and contract dramatically during operation. For example, silicon electrodes expand 300 percent, causing a lot of headaches for researchers seeking to use them in new batteries. To understand the stress, scientists first need to measure it, so a group at the Nanostructures for Electrical Energy Storage (NEES, led by the University of Maryland) Energy Frontier Research Center found a way. Their new technique measures the changes to the current through a battery under stress and lets them calculate how stress directly affects the flow of ions. With this technique, engineers can more readily identify the signs of stress in batteries, which could lead to new ways to prevent battery failures.

More Information

Larson JM, E Gillette, K Burson, Y Wang, SB Lee, and JE Reutt-Robey. 2018. “Pascalammetry with Operando Microbattery Probes: Sensing High Stress in Solid-State Batteries.” Science Advances 4(6):eaas8927. DOI: 10.1126/sciadv.aas8927

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.