Inside Unmanned Systems

JUN-JUL 2017

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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AIR, LAND, MARINE POWER 56 unmanned systems inside   June/July 2017 may be able to store as much energy as lithium-ion batter- ies, while being smaller, lighter, cheaper and safer. Lithium-ion batteries have become infamous for danger- ous incidents resulting from overheating. For instance, the batteries were at the heart of Samsung's problems with the Galaxy Note 7 smartphone, which could catch fire—leading to a global recall of the device last October. Such concerns led the U.S. Navy to research alterna- tives to lithium-ion batteries, said Debra Rolison, head of the advanced electrochemical materials section at the Naval Research Laboratory. Zinc-based batteries are not prone to fire and can, in principle, rival or surpass lithi- um-ion batteries in terms of energy per unit mass as well as energy per unit volume. In addition, zinc is cheap and widely available—it is the fourth-most mined material on the planet, with more than 14 million tons of it mined annually, said Michael Burz, founder and president of energy technology firm EnZinc, Inc., in San Anselmo, California, which helped engineer the new batteries. Zinc-based batteries are already the go-to batteries for single-use applications, Rolison said. However, they were not considered rechargeable because of their tendency to grow electrically conductive whiskers known as dendrites inside them. Such dendrites can grow long enough to cause short circuits, typically leading zinc-based batteries to die after several cycles of discharging and recharging, she said. Now Rolison, Burz and their colleagues have devel- oped a zinc-based battery with an internal structure that can quell the formation of dendrites. The zinc making up the battery's negatively charged electrode, or anode, has a porous, sponge-like architecture that helps elec- tric charge move uniformly across it when the battery discharges and recharges. This uniform distribution of charge makes it physically difficult for dendrites to form. The scientists paired their zinc anode with a positively charged electrode, or cathode, made of nickel. In experi- ments, such batteries could withstand more than 50,000 cy- cles of discharging and recharging. The researchers detailed their findings in the April 28 issue of the journal Science. Furthermore, the scientists showed this battery could deliver the same amount of energy as a lithium-ion battery in a smaller, lighter package. For instance, they estimated a zinc-nickel version of the 24 kilowatt-hour battery used in earlier models of the Nissan Leaf electric car could de- liver the same amount of energy but weigh about a third Photos courtesy of U.S. Naval Research Laboratory. Jeffrey Long, from the U.S. Naval Research Laboratory's Chemistry Division, holds an approximately 5 sq. cm disk of a prototype zinc "sponge" anode. Long is part of a team at NRL with a breakthrough for nickel–zinc batteries in which a three-dimensional (3-D) zinc sponge replaces the powdered zinc anode traditionally used. With 3-D zinc, the battery provides an energy content and rechargeability that rivals lithium-ion batteries while avoiding the safety issues that continue to plague lithium. The sponge can be made in virtually any desirable shape and size for different applications. Their research appears in the April 28th, 2017 issue of Science, the premiere journal of the American Association for the Advancement of Science. Zinc may enable a safe, cheaper and smaller battery. This NRL team found a way to make zinc-based batteries reusable. Naval Researchers.

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