Headline, February27, 2014

"' REMEMBER-R​EMEMBER ?! > 

BATTERIES ^-^ BOOMERANGS "'

BUILDING a better battery has become an intense area of research. A device that could store more power in the same amount of weight as widely used Lithium cells could, for instance:

Allow smartphones to run for weeks on a single charge or an electric car to be driven non-stop for hundreds of kilometres. Among the alternatives being explored, Lithium-air batteries are a favourite.

But they can be tricky to make and unreliable. But now researchers have found a way to overcome some those shortcomings with the help of  > '''genetically modified viruses'''.

Using viruses to make batteries is not new: Dr Angela Belcher and her colleagues at  MIT  demonstrated in 2009 that it was possible by getting modified viruses to coat themselves with the necessary material required for the anode and cathode in a small button-sized lithium-ion cell.

Making  things with viruses -in this case a bacteriophage which infects bacteria but is harmless to humans -might seem unusual. But it is similar to the biosynthesis employed in nature.

Lithium air batteries oxidise Lithium at the anode and reduce oxygen at the cathode to induce a current flow. Because the oxygen comes from the air there is no need for some of the relatively heavy internal materials used in the other types of battery.

That promises a greatly increased energy density  -the amount of power that can be stored in a given weight of battery.

In a new paper in  Nature Communications the  MIT   team describes using modified viruses to make a cathode for Lithium-air battery. A cathode is usually harder to produce than an anode because it needs to be highly conductive.

The viruses were genetically engineered to capture molecules of manganese oxide  -a popular material for building Lithium-air cathodes -in solution of water.

They then bind the material into an array of  manganese-oxide nanowires with rough, spiky surfaces. Unlike the smooth nanowires made with conventional chemical processes, the spikes increase the surface area available for electrochemical reactions when the battery is charged and discharged.

A small quantity of metal, such as palladium, is added to boost conductivity. And then making things with viruses -in this case a common bacteriophage which infects bacteria but is harmless to humans  -might seem unusual. But it is similar to the biosynthesis employed in nature.

Indeed, Dr Belcher says her work was inspired by the way an abalone is genetically programmed to collect calcium from the seawater in order to grow its shell. And because the process mimics a natural technique:

Production can be carried out at a room temperature using water-based solutions, unlike conventional methods of making cathodes which are energy-intensive, and involve high temps and hazardous chemicals.

The researchers think they can produce a Lithium air battery with an energy density more than twice that of the best lithium ion cells. That make a lot of difference to portable electronic products.

A typical Lithium-ion battery can store some 150 watt-hours of electricity in one kilogram of battery  -itself a huge advance over the 45-80 watt hours of a nickel cadmium battery, let alone an old-time lead-acid battery's 30 watt-hours.

But there is some way to go. Lithium-air cells will have drawbacks too, such as sensitivity to high temp which can cause their Lithium-ion cousins to burst into flames.

So far, the researchers have successfully tested their viral material through 50 cycles of charging and recharging, which is encouraging but well short of the hundreds and thousands of cycles expected from a commercial battery.

The MIT team could be on the right road, but more work is needed before Lithium-air batteries can be used to drive electric cars two or three times farther on a single charge.

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