Advances in Nanomaterials

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ing crystals of the compounds, which can be swapped for hydrogen for an effective storage solution. According to the press release, “The work is at the proof of concept stage and is part of a $1.2 million project funded by the National Science Foundation, a collaboration between UCSD, Alfred University in upstate New York, and the University of Nevada, Reno.” n Coin-sized battery can power devices for a decade A new battery prototype developed by researchers at Oak Ridge National Laboratory may help bid farewell to charging cables and USBs, thanks to a “new and unconventional battery chemistry” that can sustain a single charge for up to 10 years. According to an ORNL press release, their findings, published in the Journal of the American Chemical Society, “challenged a long-held assumption that a battery’s three main components—the positive cathode, negative anode, and ion-conducting electrolyte—can play only one role in the device.” The electrolyte in the new design pulls “double-duty”—serving as an ion conductor and cathode supplement— and is further enabled by ORNL’s solid electrolyte, which boosts the battery’s capacity and service life. “This bifunctional electrolyte revolutionizes the concept of conventional batteries and opens a new avenue for the design of batteries with unprecedented energy density,” says ORNL’s Chengdu Liang in the release. The ORNL team was able to demonstrate the concept in what is considered to be “one of the best single-use batteries because of its high energy density, stability, and long shelf life.” The solid lithium thiophosphate (Li3PS4, LPS) electrolyte incorporated into a lithium–carbon fluoride battery resulted in a battery with an increased capacity of 26 percent. “As the battery discharges, it generates a lithium fluoride salt that further catalyzes the electrochemical activity of the electrolyte,” Liang said. “This relationship converts the electrolyte— conventionally an inactive component in capacity—to an active one.” The release notes that, depending on how the battery is engineered or used, the capacity improvement may equal years or decades of additional life. And given its small size, the battery would be particularly useful in devices where easy or desirable battery replacement or recharging is neither easy nor desirable (artificial cardiac pacemakers, radiofrequency identification devices, and remote keyless systems and sensors). The paper is “Pushing the theoretical limit of Li-CFx batteries: A tale of bifunctional electrolyte” (DOI: 10.1021/ja5026358). n advances in nanomaterials Transparent ceramics produce stronger armor windows The United States Naval Research Laboratory has developed a superior ceramic nanocrystalline spinel, highly transparent and strong, with ambitions to improve armor windows for military vehicles. Using an enhanced high-pressuresintering (EHPS) technique, NRL scientists increased spinel hardness by 50 percent over what is currently used in military armor windows. “The EHPS approach uses high pressures (up to 6 GPa) to retard bulk diffusion rates, break powder agglomerates, and reposition nanoparticles very close to each other to help eliminate porosity in the sintered ceramic,” states an NRL press release. “NRL researchers then can exploit the increased surface potential of nanoparticles for surface-energy-driven densification without coarsening.” The new technique did not decrease density or fracture resistance, as has been previously observed because of residual porosity in nanocrystalline spinel. The spinel also retained high transparency, a must for optical equipment on military vehicles. Although previous work has shown Credit: U.S. Navy; General Dynamics New and improved armor windows could find application in deckhouse windows in the new class of U.S. Navy destroyers, like the USS Elmo Zumwalt. that the Hall–Petch relationship between strength and hardness falls apart for some ceramic materials sized less than 130 nm, the NRL research shows that grain sizes down to 28 nm maintain strength and hardness. The paper, published in Acta Materialia, is “An extended hardness limit in bulk nanoceramics” (DOI: 10.1016/j.actamat.2014.01.030). n American Ceramic Society Bulletin, Vol. 93, No. 5 | www.ceramics.org 17


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