The big problem with lithium-ion batteries, widely used in mobile phones and in electric vehicle batteries, is often that greater charging power is associated with a fire hazard. Researchers at the University of Michigan say they have developed a technology that avoids this problem. As a result, it should again be possible to make higher-capacity batteries.
Because lithium ions are embedded in carbon, the capacity per gram of existing and widely used lithium batteries is quite low. Using pure liquid lithium increases capacity, but also creates a fire hazard because too many lithium atoms come together in one place, creating too much energy. The researchers say they have now found a solution to this.
Thinly coating battery
What did they do: the researchers applied a thin layer of ceramic electrolyte to the battery. The ceramic ensures that the lithium atoms do not build up and thus there is no fire risk. Meanwhile, the battery does have the capacity of a pure lithium battery: about 10 times larger than lithium ion batteries. According to the researchers, their breakthrough could well pave the way to a new generation of rechargeable batteries. "This could be a game-changer - a paradigm shift in how a battery works," said Jeff Sakamoto, U-M associate professor of mechanical engineering, who is leading the project. "What we came up with is a different approach: physically stabilising the lithium metal surface with a ceramic," Sakamoto said. "It is not flammable. We make it at almost 1,000 degrees in the air. And there is no liquid, which is now often the cause of batteries catching fire."
Even surface
There have been previous trials of applying solid-state eletrolyte ceramics, but they ultimately proved unsuccessful. The major difference in this research is that the layer applied over the battery is very even. By using new chemical and mechanical treatments, the surface is made uniform. As a result, dendrites and filaments do not form and the lithium does not leak through the ceramic one. "This not only improves safety, so it also dramatically increases capacity," Sakamoto said.
Within three hours
Although the battery can now only be made in the laboratory, the new technology may have potential. Where an average lithium battery in an electric car now takes about 20 hours to charge, this battery would take only three hours or less. Also, the battery's power did not decrease after several charges. Pure lithium can also be used to make smaller batteries, which in turn would save on the weight of, say, an eletric bicycle or car.
Source: University of Michigan/The Engineer
Photo credit: Evan Dougherty, Michigan Engineering
