Breathing Batteries Bring Big Benefits
By Chuck Squatriglia
May 25, 2009
Lithium ion batteries power cellphones, laptops and other gadgets and, soon, lots of electric cars. Researchers in the U.K. think they’ve found a way to increase their energy capactty as much as 10-fold: Make them breathe.
A typical lithium ion battery like that of the Chevrolet Volt (pictured) contains an anode of graphite, a cathode of lithium cobalt oxide (or another compound, such as lithium manganese) and a lithium salt electrolyte. Lithium ions move between the anode and cathode as they charge and discharge, sending electrons through a circuit to provide power.
Peter Bruce of the University of St. Andrews says the problem is lithium cobalt oxide is bulky and heavy. That limits the ability to increase energy density without making batteries unmanageably large, he tells New Scientist. His solution cribs from hearing aids, which use zinc-air batteries get power from the reaction between zinc and the air.
Bruce has designed a lithium-air battery prototype that swaps lithium cobalt oxide for porous carbon. The lithium ions are contained in the electrolyte, which fills the carbon like water fills a sponge. As the battery is discharged, air passes through a membrane into the carbon,where it reacts with the lithium ions and electrons in an external circuit to form solid lithium oxide, according to New Scientist.
As the battery discharges, the solid lithium oxide fills the carbon pores. When the battery is recharged, the lithium oxide decomposes again, releasing ions and clearing space in the carbon. The oxygen is released into the atmosphere.
The prototype has a capacity-to-weight ratio of 4,000 milliamp hours per gram, roughly eight times that of a cellphone battery, New Scientist reports. Bruce tells the publication a 10-fold improvement is possible but using existing lithium ion designs will probably do no more than double capacity.
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