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http://www.treehugger.com/files/2009/10/zinc-air-battery-revolt-3-times-more-energy-lithium-ion-battery-electric-cars.php?dtc=TH_rotator
Very Promising! Zinc-Air Battery Could Hold 300% More Energy Than
Lithium-Ion
by Michael Graham Richard, Ottawa, Canada on 10.29.09
Science & Technology
Buzz up!
Image: ReVolt Technology
Might This Be the One We've Been Waiting For?
7
ShareNot quite as impressive on paper as the lithium-air battery we
wrote about (which claimed 10x more energy storage than regular
lithium-ion), but it might turn out to be easier to take out of the
lab and bring to market. ReVolt Technology, a company based in Staefa,
Switzerland, claims that its Zinc-air battery can "store three times
the energy of lithium ion batteries, by volume, while costing only
half as much," and unlike other existing air batteries, this one would
be rechargeable. It is planning to start by selling small ones for
hearing aids and then progressively scale up to portable electronics
and electric cars.
The original design was created at SINTEF, and ReVolt was a kind of
spinoff designed to bring the Zinc-air technology to market.
MIT's Technology Review writes:
Unlike conventional batteries, which contain all the reactants needed
to generate electricity, zinc-air batteries rely on oxygen from the
atmosphere to generate current. [...]
making them rechargeable has been a challenge. Inside the battery, a
porous "air" electrode draws in oxygen and, with the help of catalysts
at the interface between the air and a water-based electrolyte,
reduces it to form hydroxyl ions. These travel through an electrolyte
to the zinc electrode, where the zinc is oxidized--a reaction that
releases electrons to generate a current. For recharging, the process
is reversed: zinc oxide is converted back to zinc and oxygen is
released at the air electrode. But after repeated charge and discharge
cycles, the air electrode can become deactivated, slowing or stopping
the oxygen reactions. This can be due, for example, to the liquid
electrolyte being gradually pulled too far into the pores, Henriksen
says. The battery can also fail if it dries out or if zinc builds up
unevenly, forming branch-like structures that create a short circuit
between the electrodes.
But ReVolt says it has found a way to better control that, and the
company's first products are expected to work for a many hundreds of
cycles, which would be good for portable electronics. But electric
cars will require something different, and ReVolt is also working on
that:
For electric vehicles, ReVolt is developing a novel battery structure
that resembles that of a fuel cell. Its first batteries use two flat
electrodes, which are comparable in size. In the new batteries, one
electrode will be a liquid--a zinc slurry. The air electrodes will be
in the form of tubes. To generate electricity, the zinc slurry, which
is stored in one compartment in the battery, is pumped through the
tubes where it's oxidized, forming zinc oxide and releasing electrons.
The zinc oxide then accumulates in another compartment in the battery.
During recharging, the zinc oxide flows back through the air
electrode, where it releases the oxygen, forming zinc again.
This would increase energy density, and also increase the number of
cycles before degradation (up to between 2,000 and 10,000 according to
the company).
This is very promising, but as usual with news from the lab, we'll
have to wait until it hits the market before we can know if it's
really the holy grail... |
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