Monday, January 24, 2011

Lithium air batteries

Lithium air batteries can theoretically store three times as much energy per weight unit as a lithium ion battery. The current prototypes are, however, subject to many problems. Two of them could now be solved by a new, highly efficient catalyst.

By now omnipresent, there is no end in sight to the technical development of the lithium ion batteries. One of the latest ideas is a lithium air battery that owes its name to the fact that they generate current once the light metal lithium reacts with atmospheric oxygen. Referred to the weight it can store three times as much energy as the conventional lithium ion battery.

Sounds great but this energy store has been rather unpopular so far: poor efficiency, a short life cycle ( only few charge cycles), slow performance, current and water kill them and last but not least: lithium is highly reactive; it is possible that branches grow out of the electrodes which can cause short-circuits in the battery.

The MIT people have found a solution to at least two of the inconveniences: Thanks to a new catalyst they have succeeded in increasing the efficiency of the batteries to a new record value. This catalyst consists of nanoparticles of a gold-platinum alloy. Using it the prototype of the battery could release 77 percent of the energy stored.

Image source: Yi-Chun Lu

It seems that the MIT people could have solved at least the efficiency problem with this catalyst. During discharge the lithium combines with atmospheric oxygen to lithium oxide and releases electrons. During charging both elements are separated. The new catalyst reinforces both reactions: The gold atoms help with oxidisation, the platinum atoms, however, support the separation of the oxygen. Thus less energy is wasted during charging and discharge.

Since the catalyst also alleviates the formation of lithium oxide clots that would otherwise clog the interior of the battery, it could also increase its life cycle. The future of the gold-platinum catalyst still remains to be seen because Jean-Marie Tarascon of the Université de Picardie Jules Verne is convinced of cheap manganese oxide since he has found out just recently that it has even better values than the compound of the MIT researcher, says Tarascon.

Excitement remains....

The paper: Lu, Y. et al., "Platinum-Gold Nanoparticles: A Highly Active Bifunctional Electrocatalyst for Rechargeable Lithium-Air Batteries", Journal of the American Chemical Society, 7.6.2010 (Abstract)

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