Salt water-based Li-ion battery offers both high energy, safety

Salt water-based Li-ion battery offers both high energy, safety

Technology News |
By Rich Pell

“In the past, if you wanted high energy, you would choose a non-aqueous lithium-ion battery, but you would have to compromise on safety. If you preferred safety, you could use an aqueous battery such as nickel/metal hydride, but you would have to settle for lower energy,” said Dr. Kang Xu, ARL fellow who specializes in electrochemistry and materials science. “Now, we are showing that you can simultaneously have access to both high energy and high safety.” 

Many research teams are looking at solid state batteries to tackle the problem but the liquid cells can be more flexible.

“This is the first time that we are able to stabilize really reactive anodes like graphite and lithium in aqueous media,” he said. “This opens a broad window into many different topics in electrochemistry, including sodium-ion batteries, lithium-sulfur batteries, multiple ion chemistries involving zinc and magnesium, or even electroplating and electrochemical synthesis; we just have not fully explored them yet.”

Previous research had produced a system that reached 3V. To make the leap from three volts to four, University of Maryland assistant research scientist Chongyin Yang designed a new gel polymer electrolyte coating that can be applied to the graphite or lithium anode. 

The hydrophobic coating expels water molecules from the vicinity of the electrode surface and then, upon charging for the first time, decomposes and forms a stable mixture of breakdown products that separates the solid anode from the liquid electrolyte, called the interphase. This protects the anode and allows the battery to use desirable anode materials, such as graphite or lithium metal, and achieve better energy density and cycling ability.

“The key innovation here is making the right gel that can block water contact with the anode so that the water doesn’t decompose and can also form the right interphase to support high battery performance,” said Chunsheng Wang, Professor of Chemical & Biomolecular Engineering at the University of Maryland’s A. James Clark School of Engineering.

The addition of the gel coating also makes the battery safer and boosts the energy density. Even when the interphase layer is damaged (if the battery casing were punctured, for instance), it reacts slowly with the lithium or lithiated graphite anode, preventing the fire could otherwise occur if a damaged battery brought the metal into direct contact with the electrolyte.

The next challenge is to increase the lifetime of the cells. “Right now, we are talking about 50-100 cycles, but to compare with organic electrolyte batteries, we want to get to 500 or more,” said Wang. More work also needs to be done on scaling up the technology in big cells for testing. With enough funding, the 4-volt chemistry could be ready for commercializing in about five years, said Xu.

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