Aluminium battery

Aluminium batteries or aluminum batteries are commonly known as aluminium-air batteries or Al-air batteries, since they produce electricity from the reaction of oxygen in the air with aluminium. Aluminium batteries have the highest energy density of all batteries. Yet they are not widely used because of their high cost and very limited shelf-life which have restricted their use to mainly military applications. An electric vehicle with aluminium batteries could potentially have four times the range of lead-acid batteries, which have only one-fifth of the energy per unit volume.

Al-air are primary batteries, i.e., non-rechargeable, and can also be considered to be fuel cells. Once the aluminum anode is consumed by its reaction with atmospheric oxygen at a cathode immersed in a water-based electrolyte to form hydrated aluminum oxide, the battery will no longer produce electricity. However, it may be possible to mechanically recharge the battery with new aluminum anodes made from recycling the hydrated aluminum oxide. In fact, recycling the formed aluminum oxide will be essential if aluminum air batteries are to be widely adopted.

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Electrochemistry

The anode and cathode reactions are: Al + 3OH^- → Al(OH)₃ + 3e^- and O₂ + 2H₂O + 4e^- → 4OH^-

The total reaction is: 4Al + 3O₂ + 6H₂O → 4Al(OH)₃

About 1.2 volts potential difference is created by these reactions. Cell voltage with saltwater electrolyte is around only 0.7 V. The use of potassium hydroxide electrolyte leads to a cell voltage of 1.2 V.

Commercialization

Issues

There are a number of technical problems that need to be solved in order to make Al-air batteries suitable for powering electric vehicles. Anodes made of pure aluminum are corroded by the electrolyte, so the aluminum is usually alloyed with tin or other proprietary elements. The air cathode is made from high molecular weight polymers, i.e., plastics and advanced membrane technology which allow the oxygen to diffuse through the salt water electrolyte and reach the aluminum anode. Further development work on cathodes is necessary. The hydrated alumina that is created by the cell reaction forms a gel-like substance at the anode and reduces the electricity output. This is an issue that is being addressed in the development work on Al-air cells. Additives have been developed which make the alumina to be formed as a powder rather than a gel.

Aluminium as a "fuel" for vehicles has been studied by Yang and Knickle.^[3] They concluded the following: "The Al/air battery system can generate enough energy and power for driving ranges and acceleration similar to gasoline powered cars...the cost of aluminum as an anode can be as low as US$ 1.1/kg as long as the reaction product is recycled. The total fuel efficiency during the cycle process in Al/air electric vehicles (EVs) can be 15% (present stage) or 20% (projected) comparable to that of internal combustion engine vehicles (ICEs) (13%). The design battery energy density is 1300 Wh/kg (present) or 2000 Wh/kg (projected). The cost of battery system chosen to evaluate is US$ 30/kW (present) or US$ 29/kW (projected). Al/air EVs life-cycle analysis was conducted and compared to lead/acid and nickel metal hydride (NiMH) EVs. Only the Al/air EVs can be projected to have a travel range comparable to ICEs. From this analysis, Al/air EVs are the most promising candidates compared to ICEs in terms of travel range, purchase price, fuel cost, and life-cycle cost."

Traditional Al-air batteries had a limited shelf life because the aluminum reacted with the electrolyte and produces hydrogen when the battery was not in use- although this is no longer the case with modern designs. These batteries were used as reserve batteries in some telephone exchanges, as a back-up power source. Al-air batteries could be used to power laptop computers and cell phones and are being developed for such use.

Companies

The French company Métalectrique (www.metalectrique.com) have demonstrated at the "European Research and Innovation Exhibition", Paris, June 2007, that aluminum cans can easily be used as a battery. They are currently interested in using this technology for the 3rd world: For example in Mauritania, electricity is scarce but discarded aluminium cans are plentiful.^[4]

See also

• Zinc-air battery

References

1. ^ http://www.prod.sandia.gov/cgi-bin/techlib/access-control.pl/2001/012022p.pdf
2. ^ http://www.ectechnic.co.uk/ALUMAIR.HTML
3. ^ "Design and analysis of aluminum/air battery system for electric vehicles" Shaohua Yang, Harold Knickle Journal of Power Sources 112 (2002) 162–173.
4. ^ http://www.metalectrique.com/pg003.html