Breaking the Gasoline Barrier with Metal-Air Battery Technology
The continuing economic practicality of the internal combustion engine comes from the fact that oil is relatively more efficient when directly compared to even the most advanced electric car batteries today. Despite the continued development for more and more advanced electric car models, the dominance of oil in terms of raw energy density would still keep the universal acceptance of electric vehicles at bay.
But do we have other options to improve the energy density of batteries right now? Well, the first option is to develop Lithium-ion batteries that can be used in tandem with supercapacitors. The second, more promising option is to use raw air to act as the cathode of a metal-air battery.
The Lightest Possible Cathode for a Battery
The basic principle that drives a metal-air battery is the fact that oxygen can be used as a light cathode for a battery. Current batteries have reduced maximum overall efficiency (regular usage, recharging, disposal, etc.) because the heavy metals that are used as cathodes are ultimately limited by their own density and availability (in a storage space). Oxygen, on the other hand, is a lot lighter, is readily available everywhere, and is technically inexhaustible.
That is why metal-air batteries could have efficiencies that would enable them to compete head-to-head with fossil fuels. A commercially competitive metal-air battery has the solid opportunity to completely overthrow the use of gasoline, much like how internal combustion engines have overthrown electric cars during the early 1900’s.
Commonly Known Metal-Air Battery Types
There are many metals that can be used for this kind of battery configuration. However, only a few of these configurations have the efficiencies sufficient enough to be used as a stable source of energy. Two of the most prominently observed types of metal-air batteries are:
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Zinc-air Battery
This is the oldest type of metal-air battery to have been invented. Energy is provided by the oxidized zinc, producing an electrochemical charge that can be harnessed even in small form factor batteries. An upgraded form of this battery, the zinc-air fuel cell, can be recharged by “refueling” the cell with more electrolyte paste and zinc. The main challenge for zinc-air batteries is the fact that the charge cycle is not reversible; zinc has to be manually fed to the battery after complete use. Nevertheless, it is quite efficient, holding a practical specific energy of around 500 watt-hours per kilogram (for comparison, the maximum specific energy of a Lithium-ion battery is 250 watt-hours per kilogram). -
Lithium-air Battery
The most important advantage of a lithium-air battery is that the energy cycle is theoretically easy to turn around (completely reversible), allowing the Lithium peroxide molecules to easily detach and become separate Lithium ions and oxygen atoms again. This allows for practical recharging of a Lithium-air battery in much the same way as any ordinary rechargeable battery. The calculated specific energy of a lithium-air battery, if it gets its oxygen from the battery’s surroundings, is around 11,000 watt-hours per kilogram. Converted to joules, it is around 40 megajoules per kilogram, very near to the specific energy of gasoline (45 megajoules per kilogram).
IBM is currently on a pioneering challenge to produce the very first commercially viable Lithium-air battery in the world. The battery prototypes are scheduled to arrive as early as 2013, and the company is even confident enough that the technology would gain commercial production capability by the year 2020.
Photo credit: Some rights reserved by WSDOT via Flickr
Christian Crisostomo is a researcher and an observer of humanity's technological progress. He is also a green technology enthusiast and an advocate of environment-friendly alternative energy.
