Solid-state batteries are charged and discharged in custom-made hardware designed at Georgia Tech. A smaller, modified version of the cell imaged materials during cycling.
All photos courtesy of Mathew McDowell, Georgia Tech

Eliminating liquid electrolytes in lithium-ion batteries could remove flammability risks, so dozens of organizations are experimenting with liquid-free, solid-state batteries. To get a better understanding of how those units charge and discharge, researchers at the U.S. Department of Energy’s Argonne National Lab recently used ultrabright X-rays to observe the internal evolution of the materials inside solid-state lithium batteries.

Using a roughly 2mm wide cylindrical battery, researchers at Argonne’s Advanced Photon Source (APS) beamline 2-BM, captured 3D images of structural changes during the battery charge and discharge cycles as they occurred.

Francesco De Carlo, group leader with Argonne’s X-ray Science division and a co-author of a paper highlighting the research, says high beamline sensitivity and speed made the research possible, adding, “The sensitivity helped the team differentiate between phases inside the battery with similar densities, and the speed allowed them to capture the changes inside the battery while the process was evolving.”

Images revealed how dynamic changes of electrode materials at lithium/solid-electrolyte interfaces determine the behavior of solid-state batteries. Battery operation caused 1µm-to-2µm voids to form at the interface, creating contact loss that was the primary cause of failure.

“This work provides fundamental understanding of what’s happening inside the battery, and that information should be important for guiding engineering efforts that will push these batteries closer to commercial reality in the next several years,” says Matthew McDowell, co-author of the paper and an assistant professor at the Georgia Institute of Technology. “We were able to understand exactly how and where voids form at the interface, and then relate that to battery performance.”

The solid electrolyte used in solid- state batteries boosts energy density and improves safety. However, removing lithium from electrodes can create interface voids that cause reliability issues that limit battery longevity.

“To counter this, you could imagine creating structured interfaces through different deposition processes to try to maintain contact through the cycling process,” McDowell says.

The Georgia Tech research team, led by first author and graduate student Jack Lewis, built special test cells, and four members of the team studied the changes in battery structure during a five-day, intensive experiment using X-ray computed tomography.

Georgia Tech and Argonne National Lab researchers constructed this 3D image of solid-state battery operation using X-ray tomography.

“The instrument takes images from different directions, and you reconstruct them using computer algorithms to provide 3D images of the batteries over time,” McDowell says. “We are very excited about the technological prospects for solid-state batteries. There is substantial commercial and scientific interest in this area, and information from this study should help advance this technology toward broad commercial applications.”

Argonne National Laboratory

Georgia Institute of Technology