Looking Inside an Operating Battery
Argonne scientists use X-ray beams to observe in fine detail how components move in an operating lithium battery
Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have used a cutting-edge X-ray technique to view the movements of components inside an operating battery cell. The study is one of the first times that such movements have been directly observed in fine detail — at the scale of a millionth of a meter — while a battery charges and discharges.
“It’s really exciting to be able to visualize these movements,” said Daniel Abraham, a senior materials scientist in Argonne’s Chemical Sciences and Engineering (CSE) division and one of the study’s authors. “Other researchers have previously guessed that these movements happen, but they’ve not been able to show them in such fine detail.”
The Argonne researchers wanted to visualize the movements of battery components to better understand two challenges with lithium-metal batteries. First, these batteries tend to swell and shrink when charging and discharging. Second, there is a tendency for detrimental materials to build up on the lithium metal anode’s surface.
When a lithium metal battery cell charges, lithium ions move from the cathode through the electrolyte to the anode. The anode expands as lithium atoms are deposited on its surface. During discharge, the anode contracts as lithium is stripped away. This back-and-forth process is normal.
Lithium metal is highly reactive. When deposited on the anode, the metal quickly reacts with electrolyte nearby. These reactions form a layer of material over the lithium called the solid electrolyte interphase.
A thin interphase layer can protect a battery’s health. It separates the electrolyte and lithium metal so they cannot keep reacting. Such reactions could eventually consume all of the electrolyte — and the cell would stop working.
At Argonne’s Advanced Photon Source, a DOE Office of Science user facility, the researchers used a cutting-edge technique called energy dispersive X-ray diffraction. This technique involved directing an X-ray beam into a lithium-ion battery cell as it was repeatedly charged and discharged. The cell was a small circular device known as a coin cell. It contained an anode made of lithium metal and a cathode made of a metal oxide material.
The researchers measured the changing patterns of the scattered X-ray beams. This information enabled them to map out and characterize changes in the atom arrangements in the cell’s materials. The team then used those arrangement changes to quantify the movements of the cell’s components.
“The movements we measured were caused by the anode’s expansion and contraction as lithium was deposited and stripped away,” said Abraham. “We found that the anode grew much larger than expected due to the buildup of the interphase material. We also saw that the expanding anode pushed against the cathode and separator, causing them to move as well.”
Read the full release on the research here: https://www.anl.gov/article/tiny-movements-deep-inside-a-battery
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