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Building a better battery

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The cutting edge cuts really fast. Four months ago Wired magazine ran an article on IBM’s efforts to produce a Lithium-air battery:

Under the aegis of its Battery 500 project — an effort to build a battery capable of powering a car for 500 miles — Big Blue has designed a battery that produces power by taking in oxygen and then recharges by expelling oxygen. Because its driven by the outside air, such a battery can be significantly smaller and lighter than traditional lithium ion batteries, providing a much longer life per square inch.

Researchers have long explored this sort of “lithium-air” battery, but IBM’s demonstration shows it can actually be built. “The fundamental operation of the battery is no longer in question at all,” says Winfried Wilcke, the senior manager of IBM’s project. The company believes that with this technology, it can indeed produce a car battery that can take you 500 miles.

IBM’s Lithium Air Battery project home page gives its goals:

Goal: create a powerful new battery for electric cars

* as good as gasoline
* 500 miles/800 km range per charge
* a total electric drive system comparable in size, weight and price to a gasoline drive train

At that time Scientific American carried an article explaining how much better such a battery would be compared to the Lithium ion batteries in use today:

Researchers predict a new type of lithium battery under development could give an electric car enough juice to travel a whopping 800 kilometers before it needs to be plugged in again—about 10 times the energy that today’s lithium ion batteries supply. It is a tantalizing prospect—a lighter, longer-lasting, air-breathing power source for the next generation of vehicles—if only someone could build a working model. Several roadblocks stand between these lithium–air batteries and the open road, however, primarily in finding electrodes and electrolytes that are stable enough for rechargeable battery chemistry.

Most fully charged lithium ion car batteries today will take an electric vehicle only 160 kilometers before petering out. (Nissan says its all-electric Leaf has a range of about 175 kilometers.) Plug-in electric vehicles such as the Chevy Volt have an even more limited range of up to 80 kilometers before its gas-powered motor must kick in.

Another way to gauge the lithium–air battery’s potential is to compare it to other batteries in terms of specific energy, or how much energy it produces in relation to its size. Whereas a conventional lead–acid car battery will produce up to 40 watt-hours per kilogram, a lithium ion battery maxes out at 250 watt-hours per kilogram. A lithium–air battery’s potential far exceeds 1,400 watt-hours per kilogram.

Now a very interesting paper in Science promises to improve Lithium-air batteries even further:

The rechargeable nonaqueous lithium-air (Li-O2) battery is receiving a great deal of interest because, theoretically, its specific energy far exceeds the best that can be achieved with lithium-ion cells. Operation of the rechargeable Li-O2 battery depends critically on repeated and highly reversible formation/decomposition of lithium peroxide (Li2O2) at the cathode upon cycling. Here, we show that this process is possible with the use of a dimethyl sulfoxide electrolyte and a porous gold electrode (95% capacity retention from cycles 1 to 100), whereas previously only partial Li2O2 formation/decomposition and limited cycling could occur. Furthermore, we present data indicating that the kinetics of Li2O2 oxidation on charge is approximately 10 times faster than on carbon electrodes.

The specific energy actually demonstrated by the authors is around 3500 Watt-hours per Kilogram, and there is a claim that about 50% more is achievable.

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Written by Arhopala Bazaloides

August 5, 2012 at 1:56 pm

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