Hidden within cell phones, laptops, and digital cameras, lithium-ion batteries increasingly power the world. For the first time, researchers have imaged individual lithium ions, an achievement that could lead to better battery designs.
Researchers in the past few years have devised electron microscopes that can resolve most lightweight atoms and their charged counterparts, ions. Yet the lightest atoms–hydrogen, helium, and lithium–have remained out of sight.
For this reason, scientists have had to infer the internal structure of materials in lithium-ion batteries by combining information from techniques such as X-ray diffraction and theories of how materials form.
In these batteries, lithium ions diffuse in and out of the electrodes. “If you can see lithium at the atomic level, it’s going to help us tremendously in understanding the way these materials work,” comments Michael Thackeray, a battery researcher at Argonne National Laboratory in Illinois.
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That, in turn, could lead to battery materials that produce more energy and can be recharged more times than can today’s materials, says Yang Shao-Horn of the Massachusetts Institute of Technology.
In the July Nature Materials, Shao-Horn and her coworkers at Lawrence Berkeley National Laboratory (LBL) in California and the University of Bordeaux I in Pessac, France, describe how they produced a picture of the arrangement of atoms in the electrode material lithium cobalt oxide. Using a high-resolution transmission electron microscope at LBL, the scientists took 20 pictures of lithium cobalt oxide–each one deliberately defocused a little differently–with a nearly atomic resolution of 1.6 angstroms. Using image-processing tools, the team reconstructed from those pictures a much crisper image with a resolution of 0.8 .
The reconstructed image reveals for the first time individual lithium ions in the material.
The most significant revelations may lie ahead, says Shao-Horn. She and her colleagues now aim to modify their microscopy technique to image samples in which some of the lithium ions have been removed. So far, she says, the material has been too unstable for imaging when not fully filled with lithium.
Imaging vacancies that could host lithium ions is important for designing better battery materials, concurs John Spence, who works at both Arizona State University in Tempe and LBL but is not involved in Shao-Horn’s research.
The effective resolution that Shao-Horn’s group achieved opens the door for meeting another energy challenge. Says Spence, “This throws down the gauntlet to image hydrogen for hydrogen-storage materials.” Such images may contribute to use of hydrogen as a clean-burning fuel.
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