These are illustrations of the design principles for using methyl viologen to form a stable coating that allows the stable cycling of lithium-metal batteries. Image: UC Riverside.High performing lithium-ion batteries are a key component of laptops, smart phones and electric vehicles. Currently, the negatively-charged electrodes, or anodes, are generally made of graphite or other carbon-based materials.
But the performance of carbon based materials is limited because of their weight and energy density, which is the amount of energy that can be stored in a given space. As a result, a lot of research is focusing on lithium-metal anodes.
The success of lithium-metal anodes will help enable many novel battery technologies, including lithium metal and lithium air, which can potentially increase the capacity of today's best lithium-ion batteries five to 10 times. That would mean five to 10 times more range for electric vehicles and smartphone batteries that last five to 10 times longer. Lithium-metal anodes are also lighter and less expensive.
The problem with lithium-ion batteries made with metal is that during charge cycles they uncontrollably grow dendrites, which are microscopic fibers that look like tree sprouts. These dendrites degrade the performance of the battery and also present a safety issue because they can short circuit the battery and in some cases catch fire.
A team of researchers at the University of California, Riverside has now made a significant advance in solving the more than 40-year-old dendrite problem. Their findings appear in a paper in Chemistry of Materials.
The team discovered that by coating the battery with an organic compound they were able to stabilize battery performance, eliminate dendrite growth and increase the lifetime of the battery by more than three times compared to current 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 used methyl viologen as their coating, which has been used in other applications because of its ability to change color when reduced. Dissolved in the electrolyte in a charged state, it is immediately reduced on interacting with the lithium-metal electrode to form a stable coating.
By adding only 0.5% of methyl viologen into the electrolyte, the cycling lifetime can already be enhanced by three times. In addition, methyl viologen is very low in cost and can easily be scaled up.
The stable operation of lithium metal anodes, which the researchers have achieved with the addition of methyl viologen, could allow the development of next generation high-capacity batteries, including lithium-metal batteries and lithium-air batteries. Wang cautioned, however, that while the coating improves battery performance, it isn't a way to prevent batteries from catching fire.
This story is adapted from material from the University of California, Riverside, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.