Coating boosts lithium metal battery performance

April 18, 2017 //By Nick Flaherty
UCR researchers use methyl viologen for stabilizing metal anodes
US researchers have developed a coating for lithium metal battery anodes that can increase the performance by a factor of three.

The University of California at Riverside (UCR) has filed a patent for the process, which uses a low cost organic material to coat the anode.  

Using lithium metal anodes successfully in lithium metal and lithium air batteries could increase the capacity of today's best lithium-ion batteries five to 10 times. Lithium metal anodes are also lighter and less expensive. The problem is that whilst charging these batteries grow fibres of metal, called dentrites, which can cause short circuits and in some cases cause the battery to catch fire.

The researchers found that by coating the battery with an organic compound called methyl viologen they could eliminate dendrite growth and increase the lifetime of the battery by more than three times compared to the current standard electrolyte used with lithium metal anodes.

"This has the potential to change the future," said Chao Wang, an adjunct assistant professor of chemistry at UC Riverside who is the lead author of the paper. "It is low cost, easily manipulated and compatible with the current lithium ion battery industry."

The researchers designed a new strategy to form a stable coating to enhance the lifetime of lithium-metal anodes. They used methyl viologen, which has been used in other applications because of its ability to change colour when reduced.

The methyl viologen molecule used by the researchers can be dissolved in the electrolytes in the charged states. Once the molecules meet the lithium metal, they are immediately reduced to form a stable coating on top of the metal electrode.

By adding only 0.5% of viologen into the electrolyte, the cycling lifetime can already be enhanced by three times. Methyl viologen is also very low in cost and the whole process can easily be scaled up for volume battery production.

However, while the coating improves battery performance, it isn't a way to prevent batteries from catching fire, says Wang.

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