Aluminium battery

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Battery specifications
Energy/weight	1300 W·h/kg^[1]
Energy/size	N/A
Power/weight	200 W/kg
Nominal Cell Voltage	1.2 V

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. They have the highest energy density of all batteries, but they are not widely used because of previous problems with cost, shelf-life, start-up time and byproduct removal, which have restricted their use to mainly military applications. An electric vehicle with aluminium batteries could have potentially ten to fifteen times the range of lead-acid batteries with a far smaller total weight^[1].

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

1 Electrochemistry
2 Commercialization
- 2.1 Issues
- 2.2 Companies
3 See also
4 References
5 External links

[edit] Electrochemistry

The anode oxidation half-reaction is: Al + 3OH^- → Al(OH)₃ + 3e^-

The cathode reduction half-reaction is: 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.

[edit] Commercialization

[edit] Issues

Aluminium as a "fuel" for vehicles has been studied by Yang and Knickle ^[1]. 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.

There are some technical problems still to solve though to make Al-air batteries suitable for powering electric vehicles. Anodes made of pure aluminium are corroded by the electrolyte, so the aluminium is usually alloyed with tin or other proprietary elements. 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. For example, additives have been developed which form the alumina as a powder rather than a gel. Also alloys have been found to form less of the gel than pure aluminium.

Modern air cathodes are made from PTFE and Carbon layers surrounding a catalyst and a Nickel foam. The oxygen from the air passes through the PTFE then diffuses through the electrolyte to reach the aluminium anode. These cathodes work well but they can be expensive.

Traditional Al-air batteries had a limited shelf life^[2] because the aluminium reacted with the electrolyte and produced 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.

[edit] Companies

The French company Métalectrique (www.metalectrique.com) demonstrated at the "European Research and Innovation Exhibition", Paris, June 2007, an aluminium can battery and have since made a 6-pack "trash power" battery for the 3rd world, where electricity is scarce but discarded aluminium is often plentiful. ^[3]