UC San Diego NanoEngineering Professor Shirley Meng While the heat treating approach to reversing the defects is labor intensive and not likely to scale, the physics and materials science-based approach to characterizing and then addressing the nano-scale defects offers promise for finding new solutions to the voltage fade problem. They put the heat-treated cathodes into new batteries and tested them at a range of voltages going up to 4.7 volts, demonstrating that the voltage fade had been reversed. Knowing the origin of voltage fade, the team showed that heat treating the cathode materials eliminated most of the defects and restored the original voltage. By combining experimental evidence with theory, the research team concluded that the nucleation of this specific type of dislocation results in voltage fade. ![]() “Discovering these dislocations was a big surprise: if anything, we expected the extra atomic layers to occur in a completely different orientation,” said Singer, who is now on the faculty at Cornell University. "The dislocations are extra atomic layers that don’t fit into the otherwise perfectly periodic crystal structure,” said Andrej Singer, the lead author who performed this work as a postdoctoral researcher at UC San Diego. In particular, the researchers identified nanoscale defects or dislocations in Lithium-rich NMC cathode materials as the batteries charged at a range of voltages going up to 4.7 volts. The new research explains why this happens in Lithium-rich NMC cathode materials. (Ex: Can the world’s most promising electric-car battery be saved? in a July 2014 Quartz article by Steve LeVine.)Īfter a battery goes through a series of charge-discharge cycles, its voltage fades and the amount of energy it can hold, and release later for use, also fades. These cathode materials have garnered considerable attention over the years as promising components for better rechargeable batteries for electric vehicles. Researchers led by a University of California San Diego team have published work in the journal Nature Energy that explains what’s causing the performance-reducing “voltage fade” that currently plagues a promising class of cathode materials called Lithium-rich NMC (nickel magnesium cobalt) layered oxides.
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