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article imageLithium-air batteries could power electric cars

By Tim Sandle     Apr 30, 2017 in Technology
One thing holding back progress with electric cars are the batteries needed to power such vehicles. Considerable promise comes from lithium-air batteries, which enable electric cars to drive farther on a single charge.
Prototype lithium-air batteries have over three times the capacity of conventional lithium-ion batteries, according to technologists from the U.S. Department of Energy's Pacific Northwest National Laboratory. To get to this stage considerable effort has gone into the design and development of the batteries, especially in relation to understanding the reactions that occur as the battery charges and discharges electricity. Central to this is the process whereby oxygen blows bubbles inside the lithium-air battery when it discharges. Controlling this decreases the amount of wear and tear on the battery.
Control has come thanks to advances in imaging technology. This has enabled researchers to see how bubbles inflate and later deflate inside a nano-sized battery. Commenting on this, lead researcher Professor Chongmin Wang explains: "If we fully understand the bubble formation process, we could build better lithium-air batteries that create fewer bubbles. The result could be more compact and stable batteries that hold onto their charge longer."
The new images have been captured by an advanced environmental transmission electron microscope. This is a type of scanning electron microscope that allows for the option of collecting electron micrographs of specimens that are "wet," uncoated, or both by allowing for a gaseous environment in the specimen chamber.
For the imaging the scientists constructed a tiny battery within the microscope's column. This enabled them to watch as the battery charged and discharged inside. Some of the video footage is shown below:
Video enabled the researchers to propose that as the battery discharges, a bubble of lithium superoxide is propelled out from the battery's positive electrode. The emergent sphere then becomes coated with lithium oxide. The superoxide inside of the sphere then moves through a chemical reaction. The reaction forms lithium peroxide and oxygen. Following this, oxygen gas is released, leading to the bubble becoming inflated. As the battery charges, lithium peroxide eventually decomposes, which leaves the bubble to deflate. This new insight provides a good foundation for future lithium-air battery designs and optimization for use in electric cars.
The research has been published in the journal Nature Nanotechnology. The research is called "Revealing the reaction mechanisms of Li–O2 batteries using environmental transmission electron microscopy."
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