We are accustomed to driving autos and hybrids where we burn gasoline, and add more fuel to continue our journey. Traditionally, rechargeable batteries have taken a different direction. We regenerate the power, although they too do eventually wear out. Aluminum-air technology merges these streams of thought. What if, it argues, we slotted in a new part when it wears out.
Key Components of Aluminum-Air Batteries
Starting from the nearside of the image, the silvery aluminum plate serves as both negative terminal and sacrificial fuel. When air and a caustic water solution circulate at the cathode, they form hydroxyl-ions. These ions comprise equal parts of hydrogen and oxygen atoms hence the name.
The hydroxyl-ions react with the aluminum plate through the separator to produce electricity. Researchers claim aluminum air batteries deliver 4.25 kilowatts of energy per kilogram of aluminum expended. They believe 60 such cells could power a five-passenger vehicle traveling at 55 mph for 250 miles without requiring replenishing. This is between 10 and 15 times the power of a lead-acid battery.
So Why Are Lithium-Ion Batteries Still the Norm
The devil is still in the detail. In theory, aluminum-air batteries should be a bargain. The sacrificial aluminum plate is cheap provided we recycle it. On that basis, the kilogram of material producing the 4.25 kilowatts of energy could cost as little as a dollar. This should make these batteries natural candidates for electric vehicles, and knock lithium-ion out too.
The remaining challenge is the cost of the cathodes. They comprise a nickel-grid current collector, a reactive layer of carbon with a catalyst, and a porous film that prevents electrolyte from leaking. The design could otherwise serve cellphones and laptops well, in addition to UPS applications. However for now, aluminum-air batteries remain largely in the military domain.
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