With a strong enough current, “true dendrites” form, which can easily and very quickly penetrate the separator to short the battery.Īt this point, Bai said, “our unique transparent cell revealed that the voltage of battery could look quite normal, even though the separator has been penetrated by a lithium metal filament. The study found that a nanoporous ceramic separator can block whiskers up to a certain current density, after which surface growths can slowly penetrate the separator. These growths are all related to the competing reactions in the region between the liquid electrolyte and the metal deposits. Figure C | Surface growths penetrate the separator Figure B | Whisker growth is blocked by the separatorĪnd within those two limits there exists the dynamic transition from whiskers to dendrites, which Bai calls “surface growth” (see Figure C). (Images: Peng Bai)īelow the lower limit you have whiskers growing from the root (see Figure B). Figure A | True dendrites quickly penetrate the separator. Those are “true dendrites” (see Figure A ). “If you use very high current, it builds at the tip to produce a treelike structure,” Bai said. They also outline at which current each growth mode appears. His team has identified three distinct types of fingers, or growth modes, in these lithium metal anodes. “That’s why after so many years this problem has never been solved.” ![]() “If you call them all dendrites, you’re looking for one solution to solve actually three problems, which is impossible,” Bai said. ” As they spread from the lithium metal plating, they can penetrate the separator in the battery, leading to a short circuit.īut not all “fingers” are the same. Researchers have referred to these fingers as “ dendrites. ![]() “The problem is that the lithium metal plating is not uniform,” Bai said. They have been minimally successful by removing the graphite anode, then reducing the lithium ions with electrons during recharge, a process which forms a thin plating of lithium metal. “With half of the lithium-ion-hosting electrode materials empty at all times,” Bai said, “you are wasting half of your space.”Įngineers have known that they could build a more energy-dense battery (a smaller battery with a similar output capabilities) by discarding some of the dead weight that comes with half of the host materials always being empty. The process is reversed as the battery charges. When the battery discharges, lithium ions empty out of the anode, passing through the liquid electrolyte, and move into the cathode. The separator is wetted by a liquid called an electrolyte. BaiĪ lithium ion battery is made of three layers: one layer of low-voltage material (graphite) called the anode one of high-voltage material (lithium cobalt oxide) called the cathode and a layer of porous plastic which separates the two. It turns out, engineers had been looking for one solution to what turns out to be three problems. ![]() Peng Bai, assistant professor in the School of Engineering & Applied Science, has identified three key current boundaries when it comes to these energy-dense lithium metal batteries. The result of their work has recently been published online in the journal Joule. Louis have new insights into the cause - or cause s - of these issues, paving the way for smaller, safer, more energy-dense batteries. Researchers at Washington University in St. Beyond these existing problems, when researchers attempt to shrink these batteries without compromising the performance, the results are even more unstable and prone to short-circuiting engineers have not been able to move past these issues. ![]() Lithium ion batteries already have a less-than-stellar reputation: think exploding cell phones or fires on airplanes. To make a longer-lasting battery, it needs to be bigger, and bigger isn’t better when it comes to cell phones or electric cars - not to mention pacemakers. As our love of gadgets grows, so do demands for longer lasting batteries.
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