The slow rate of battery improvement is responsible for many of the shortcomings in modern technology. Your smartphone might be much faster than it was a few years back, and your laptop can last most of a day on a charge, but think about how much better they could be if power wasn’t in such short supply. One of the most promising technologies that could boost batteries into the future is known as Lithium-air. They have excellent capacity, but tend to break down in a matter of weeks. A new design that tweaks the Lithium-air reaction could finally make these batteries viable for long-term use.
Lithium-air batteries are appealing because unlike a regular lithium-ion battery, you don’t need all the reactants bottled up inside the cells. At one electrode, you have lithium metal, and at the other the lithium reacts with oxygen in the air. Charging a Lithium-air battery strips the oxygen off the electrode, returning it to the environment. The result is a much higher energy density — up to five times more in some designs.
If you’ve spent any time studying chemistry, you can probably guess at the problem — both lithium and oxygen are highly reactive, so exposing the electrode to air ensures it’ll deteriorate quickly. Researchers at the University of Illinois at Chicago and at Argonne National Laboratory believe they’ve addressed the stability issues of Lithium-air batteries with a new design.
The new battery design protects the lithium metal anode with a coating of lithium carbonate. That allows lithium ions from the anode to enter the electrolyte while keeping unwanted compounds from reaching the anode. It’s easy to create this protective layer, too. The researchers just had to run a few charge-discharge cycles with a pure carbon dioxide atmosphere, and a crystal mesh of lithium carbonate accumulated.
The cathode is where oxygen enters a Lithium-air battery. The team built this component from molybdenum disulfide, a material that generates a thin film of lithium peroxide from the battery’s normal reactions. This layer is inert in the presence of air, so it protects the cathode from unwanted reactions.
The team started with computer simulations, and then developed hardware to test in a simulated atmosphere with realistic nitrogen, oxygen, and water ratios. In testing, the prototype battery (top) managed to last 750 cycles, which is the equivalent of several years of use. The next step is to test the design in the real world, which could eventually lead to commercial versions of the Lithium-air batteries.
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