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Batteries: Scientists see how and where disruptive structures form and cause voltage fading

High angle annular dark field scanning transmission electron microscopy images showing the structural transformation from layered (left) to spinel (right) during the cyclic charge/discharge process. (Phys.org)—Starting as a few atoms long, thorns forming on the electrode’s surface in a specialized lithium battery cause the battery to gradually fade, according to scientists at Pacific Northwest National Laboratory (PNNL) and Argonne National Laboratory. Working with powerful imaging technologies in DOE’s Environmental Molecular Sciences Laboratory (EMSL), the team determined that a kind of thorn with the crystallographic spinel structure grows out of the electrode material and eventually leads to the complete conversion of the whole electrode material into the spinel structure. Furthermore, growth of this spinel structure liberates lithium oxide molecules, causing cracking and pitting. The damaged electrode thereby fades, releasing less energy with each charge/discharge cycle. Ads by Google Electric Cars on Sale. – 2013 Big Sale! Further Reduction on Electric Cars. Save Big Today. – LowerPrices.us/Electric-Cars “The changes to the structure are pretty subtle after each cyclic charge/discharge of the battery,” said Dr. Chongmin Wang, a PNNL researcher who led the study. “Atomic-level imaging provides the opportunity to get a fundamental picture of how does this type of subtle change evolves.” Increasing our nation’s independence from fossil fuels for our transportation fleet requires energy storage. A lithium-rich layered composite could increase batteries’ energy density by more than 50 percent. However, the battery fades. With repeated use, the voltage and amount of energy that can be reversibly stored and released gradually declines. The cause is a change or transformation in the composite, but how and where the transformations or phase transitions occur was under debate. By taking and analyzing atomic-resolution images of the battery’s electrode before and after use, the team answered the questions. “These findings and the follow-on studies are critical for applications, including energy storage and electric vehicles,” said Dr. Jun Liu, a key player in the Joint Center for Energy Storage Research and a PNNL materials scientist on the study.

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