Image: ReVolt Technology
Might This Be the One We've Been Waiting For?Not 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.
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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