This illustration shows how the researchers were able to image and stress-test a lithium dendrite under an atomic force microscope tip. Image: Zhang Lab/Penn State.Lithium-ion batteries often grow needle-like structures known as dendrites or whiskers between their electrodes that can short out the batteries and sometimes cause fires. Now, an international team of researchers has found a way to observe these structures as they grow, to understand ways to stop or prevent their appearance. The researchers report their findings in a paper in Nature Nanotechnology.
"It is difficult to detect the nucleation of such a whisker and observe its growth because it is tiny," said Sulin Zhang, a professor of mechanical engineering at Penn State. "The extremely high reactivity of lithium also makes it very difficult to experimentally examine its existence and measure its properties."
Lithium whiskers and dendrites are needle-like structures only a few hundred nanometers in thickness that can grow from a lithium-based negative electrode through either liquid or solid electrolytes toward the positive electrode, shorting out the battery and sometimes causing a fire.
The collaborative team from Penn State, the Georgia Institute of Technology and several universities in China successfully grew lithium whiskers inside an environmental transmission electron microscope (ETEM) by using a carbon dioxide atmosphere. The reaction of carbon dioxide with lithium forms an oxide layer that helps stabilize the whiskers.
Innovatively, the researchers used an atomic force microscope (AFM) tip as a counter electrode, and the resulting integrated ETEM-AFM technique allowed them to simultaneous image whisker growth and measure the growth stress. At high enough growth stress, the whiskers can penetrate and fracture the solid electrolyte, allowing them to continue growing and eventually short-circuit the cell.
"Now that we know the limit of the growth stress, we can engineer the solid electrolytes accordingly to prevent it," Zhang said. Lithium metal-based all-solid-state batteries are desirable because of their greater safety and higher energy density.
This new analysis technique will be welcomed by the mechanics and electrochemistry communities, and be useful in many other applications, Zhang said. Next up for the team is to look at the dendrite as it forms against a more realistic solid-state electrolyte under a transmission electron microscope to see exactly what happens.
This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.