- Aluminium battery
EtoW= 1300 W·h/kg [http://cat.inist.fr/?aModele=afficheN&cpsidt=14442338 Design and analysis of aluminium/air battery system for electric vehicles" Shaohua Yang, Harold Knickle Journal of Power Sources 112 (2002) 162–173.] ] (theoretical 3.5kWh/kg thus 37 percent eff.) molAl / 0.027kg * 3 mol e- / mol Al * 9.5e4C / mol e- * As / C * h / 3600s * Watt / VoltAmp * 1.2V / cell * kW / 1e3 Watts = 3.5 kWh / kg cell ignoring the weight of the oxygen and nonconsumables (electrolyte, and positive electrode)
PtoW= 200 W/kg
Aluminium batteries or "aluminum batteries" are commonly known as aluminium-air batteries or Al-air batteries, since they produce electricity from the reaction of
oxygenin the airwith 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.
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.
anodeoxidation half-reactionis: Al + 3OH- → Al(OH)3 + 3e- Standard Red Pot = -2.31V
cathodereduction half-reaction is: O2 + 2H2O + 4e- → 4OH- Standard Red Pot = + 0.40V
The total reaction is: 4Al + 3O2 + 6H2O → 4Al(OH)3 Cell Pot = 0.40 V - -2.31V = 2.71V
About 1.2 volts
potential differenceis 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.
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 consist of a reactive layer of
Carbonwith a Nickelgrid current collector, a catalyst (eg. Cobalt) and a porous, hydrophobic PTFEfilm that prevents electrolyte leakage. The oxygen in the air passes through the PTFEthen reacts with the water to create hydroxide ions. These cathodes work well but they can be expensive.
Traditional Al-air batteries had a limited shelf life [ [http://www.ectechnic.co.uk/ALUMAIR.HTML Aluminium/air batteries ] ] 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. The problem can be avoided by storing the electrolyte in a tank outside the battery and transferring it to the battery when it is required for use.
These batteries can be used as reserve batteries in 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.
The French company Métalectrique ( [http://www.metalectrique.com 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. [ [http://www.metalectrique.com/news.html News ] ]
Different types of aluminium batteries had been investigated.They include:
Aluminium-Chlorine battery.This battery was patented by
United States Air Forcein the 1970s.They were designed mostly for militaryapplications.They use aluminium anodes and chlorine on graphitesubstrate cathodes.Required elevated temperatures to be operational.
Aluminium-Iodine secondary cell have been investigatedby some Chinese researchers.
Aluminium-Sulphur batteries.American researchers worked on thosebatteries.There are great claims,also it seems that they are stillfar from mass production.It's unknown if they are rechargeableor not.
* [http://www.exo.net/~pauld/activities/AlAirBattery/alairbattery.html Simple homemade aluminum-air battery]
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