ADELPHI, Md. (Aug. 22, 2016) -- Scientists were discussing an altogether different project when they came across the notion that increasing solubility in lithium salt could lead to something that stopped the conversation for a moment with near total silence and started a new research path.
"The orchestra didn't play, but you get that feeling all at once that there was every reason to believe it would work," said Arthur Von Wald Cresce, a U.S. Army Research Laboratory materials scientist. "And it did."
It was the end of last year when ARL scientists and their colleagues at the University of Maryland began formally exploring lithium ion aqueous batteries.
Traditional lithium ion batteries are very energetic. The batteries are used commercially in cell phones, laptops and many other portable devices because of the amount of energy they harness in such a small space. These conventional batteries can perform outside the stability of their liquid electrolytes with the help of a protective shield.
What scientists are beginning to understand is that the salt that they use in high concentrations for the aqueous batteries gives a new layer of lithium fluoride that will match the conventional lithium ion coating, Cresce said.
"The main problem with lithium ion batteries has always been safety," Cresce said. "The aqueous lithium ion battery could take away a lot of the danger of fire. What we're trying to do is to make sure that the battery remains safe, it remains nonflammable, but that we get as much capacity out of the battery as possible."
The researchers are in the early stages of understanding what is happening with this aqueous electrolyte as it interfaces with the anode, the negative electrode, Cresce said.
"Right now lithium ion batteries are engineered to take a loss in energy density for a gain in safety," Cresce said. "For future applications such as car batteries, capacity is vital because the space is so limited.
"In the Army, we are concerned about micro grids -- the harvesting, generating and distribution of electricity for a very reliable energy storage bank that Soldiers could have in their camp to run equipment without the danger of fire or need to bring in as much fuel is a practical application for this research."
Scientists from the University of Maryland and ARL published their findings in the journal Science in November 2015.
"The lithium fluoride layer that forms when we use the salt in very high concentrations is something that we are just getting to know now. We're just understanding where it decided to nucleate and how it grows. It is a challenge to look at the reaction as it is happening," Cresce said.
They used experimental materials that work well in the laboratory but are also expensive and difficult to produce, so the next step is to find better anode materials for the next experiments.
"The proximity of everything makes this electrolyte special and unusual," Cresce said. "You think of the Army as being regimented. Our organization gives leeway to explore topics that are unusual and difficult. It's difficult to justify being able to be curious, but many of the developments that we depend on today started with a similar curiosity about things like radio, wireless communications and radar. I'd like to think we are contributing by taking chances."
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The U.S. Army Research Laboratory is part of the U.S. Army Research, Development and Engineering Command, which has the mission to ensure decisive overmatch for unified land operations to empower the Army, the joint warfighter and our nation. RDECOM is a major subordinate command of the U.S. Army Materiel Command.
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