BETTER BATTERY?: Researchers have designed a lithium-based battery capable of storing more energy for the same weight.
Image: J. Ash Bowie/Wikimedia Commons
Researchers at the Massachusetts Institute of Technology have come one step closer to replacing the lithium-ion batteries that power phones, laptops and electric cars with a device that stores far more energy for the same weight.
The device is known as a lithium-air or lithium-oxygen battery. Charged lithium atoms react with the oxygen from air flowing through the apparatus, forming lithium peroxide, and deposit on the structure. The peroxide can then be broken down to release electricity.
In a paper published in the journal Energy & Environmental Science, a team of materials scientists and mechanical engineers refined this design and made it hold almost four times the electricity of a lithium-ion battery by weight.
"The key benefit, I think, is energy density," said Robert Mitchell, a Ph.D. student in materials science and engineering. Mitchell and Betar Gallant, a Ph.D. student in mechanical engineering, were the co-lead authors of the study. "In the last couple of years, there has been a flurry of new interest in these batteries," said Mitchell.
The electrode of the battery is formed using carbon nanofibers: thin, hollow cylinders of pure carbon. The nanofibers are grown and aligned, forming a structure not unlike a carpet or a lawn. "The unique morphology of these carbon electrodes creates a low-density scaffold for lithium peroxide," said Mitchell. The open spaces in the structure provide lots of room for electricity to be stored in the form of lithium compounds.
Searching for a proper catalyst
The battery itself is also much lighter than existing rechargeable cells. "The reason has to do with how the cathode works," said Gallant. "We directly react the lithium with oxygen instead of cobalt," the material most commonly used in current-generation lithium-ion batteries. "It can provide a longer range for an electric vehicle for a given weight," she said.
Nonetheless, the new device has some limitations. "One challenge with lithium-air batteries is the poor round-trip efficiency," said Mitchell. "The voltage required to decompose the lithium peroxide is quite large"; i.e., the voltage coming out of the cell is lower than the voltage required to charge it.
The team is investigating some potential solutions. "There's a lot of interest in new catalysts to increase efficiency," said Mitchell. The catalysts would lower the amount of energy needed to break down the lithium peroxide. Mitchell said that practical applications for lithium-air cells are still years off.
However, it isn't just the potential of this research that intrigued Gallant. "What's really exciting about the structure we developed is that we could see lithium peroxide structures develop, grow and degrade," said Gallant. The researchers are hoping to study how the material deposits on the structure, along with tuning the carbon density, in order to continue improving the device's efficiency.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500
See what we're tweeting about
3 Comments
Add CommentI don't see the advantage of this new configuration as compared to M.I.T.'s previous Lithium Iron Phosphatase battery (now produced by A123 Inc.), whose power density was already 5 times that of the conventional cobalt oxide setup. Carbon nanotubes may increase power density simply by porosity alone, so what is the big deal? Stanford U. tried silicon nanowire for the anode at even greater densities without the loss of efficiency. Trying to top a class act is hard, but that doesn't mean you should go around name-dropping "carbon nanotubes" just to attract funding from less sophisticated investors.
Reply | Report Abuse | Link to this"OBagle" - I agree. There is much better materials in the works than the lithium-air. I think it was MIT who is working on the sludge battery for electric cars that works a thousand times better than the lithium-air. The lithium-air is a waste of money and time and it is not worth reporting on at this early stage in its life, because by the time they get all the kinks worked out, we will have an incredible battery with the sludge that will eliminate range rage.
Reply | Report Abuse | Link to thisI think it is not a good idea to dismiss any of these various advanced battery/capacitor technologies. There are a LOT of variables involved in making a technology commercially viable. There are a lot of contenders for various applications that might be much better than what we're using now, but most of them will probably never be commercially successful. Trying many different techs is just prudent. Once one clearly makes it to the level where it can be commercial that doesn't mean others should be abandoned either, they may be better or have advantages in some applications, etc.
Reply | Report Abuse | Link to this