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NMR imaging used to catch performance-killing flaws inside batteries

Batteries based on lithium now power everything from our watches to our cars, and we’ve made major strides towards stuffing more energy into them more quickly over the last several years. But there are limits to how quickly a battery can charge, and pushing past them can cause the lithium to form metallic microstructures within the battery. These can do ugly things like creating a short between the electrodes or puncturing the membranes that contain the battery’s electrolyte.

Most techniques that could image these miscrostructures involved taking the battery apart, meaning that we could only take static images of the impact of charge/discharge cycles on the battery. One of the best techniques for non-invasive imaging, NMR, relies on radiofrequency signals that simply don’t penetrate beyond the surface of a battery. Now, some researchers have figured out that there are conditions that enable the use of NMR to peek inside a battery—and they happen to be the formation of the microstructures we care about.

NMR relies on the fact that the nuclei of atoms have spins. Place a material in a strong magnetic field, and the spins will all align along the field, lining up either parallel or antiparallel to the field lines. Once they’re lined up, a small jolt of energy—corresponding to radiofrequency radiation—is enough to get them to flip their alignment. We can then read the changes in the absorption of these frequencies to determine things about a material’s composition and structure.



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