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Aluminium–air battery

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High-electrical energy density storage device

For the rechargeable battery, see aluminium-ion battery.

{{Cite journal | last1 = Yang | first1 = S. | doi = 10.1016/S0378-7753(02)00370-1 | title = Design and analysis of aluminum/air battery system for electric vehicles | journal = Journal of Power Sources | volume = 112 | pages = 162–201 | year = 2002 | issue = 1 | bibcode = 2002JPS...112..162Y }}"},"EtoS":{"wt":"N/A"},"PtoW":{"wt":"200 [[watt|W]]/kg"},"NomV":{"wt":"1.2 [[volt|V]]"}},"i":0}}]}'>Aluminium–air batterySpecific energy1300 (practical), 6000/8000 (theoretical) W·h/kg[1]Energy densityN/ASpecific power200 W/kgNominal cell voltage1.2 V

Aluminium–air batteries (Al–air batteries) produce electricity from the reaction of oxygen in the air with aluminium. They have one of the highest energy densities of all batteries, but they are not widely used because of problems with high anode cost and byproduct removal when using traditional electrolytes. This has restricted their use to mainly military applications. However, an electric vehicle with aluminium batteries has the potential for up to eight times the range of a lithium-ion battery with a significantly lower total weight.[1]

Aluminium–air batteries are primary cells, i.e., non-rechargeable. 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 is possible to mechanically recharge the battery with new aluminium anodes made from recycling the hydrated aluminium oxide. Such recycling would be essential if aluminium–air batteries were to be widely adopted.

Aluminium-powered vehicles have been under discussion for some decades.[2] Hybridisation mitigates the costs, and in 1989 road tests of a hybridised aluminium–air/lead–acid battery in an electric vehicle were reported.[3] An aluminium-powered plug-in hybrid minivan was demonstrated in Ontario in 1990.[4]

In March 2013, Phinergy[5] released a video demonstration of an electric car using aluminium–air cells driven 330 km using a special cathode and potassium hydroxide.[6] On May 27, 2013, the Israeli channel 10 evening news broadcast showed a car with Phinergy battery in the back, claiming 2,000 kilometres (1,200 mi) range before replacement of the aluminium anodes is necessary.[7]

Electrochemistry<br>[edit]

The anode oxidation half-reaction is Al + 3OH−<br>→ Al(OH)<br>3 + 3e− -2.31 V.

The cathode reduction half-reaction is O<br>2 + 2H<br>2O + 4e− → 4OH−<br>+0.40 V.

The total reaction is 4Al + 3O<br>2 + 6H<br>2O → 4Al(OH)<br>3 +2.71 V.

About 1.2 volts potential difference is created by these reactions and is achievable in practice when potassium hydroxide is used as the electrolyte. Saltwater electrolyte achieves approximately 0.7 volts per cell.

The specific voltage of the cell can vary depending upon the composition of the electrolyte as well as the structure and materials of the cathode.

Other metals can be used in a similar way, such as lithium-air, zinc-air, manganese-air, and sodium-air, some with a higher energy density. However, aluminium is attractive as the most stable metal.[8]

Anode<br>[edit]

Aluminium (Al) has been widely used as an anode material in metal-air batteries due to its high energy density, recyclability, and abundance. However, challenges with Al anodes include corrosion and passivation. Impurities in commercially available aluminium lead to the formation of layers that impair performance. Corrosion reactions produce hydrogen and form aluminium hydroxides, while the formation of an oxide film upon exposure to air or water further limits functionality.[9]

Improving Al anode performance involves optimizing grain size and crystal orientation, as finer grain structures enhance corrosion resistance and electrochemical activity. The study done by Fan and Lu examined the relation between the grain size and the anode performance.[10] In this study, aluminium anodes with finer grain sizes were created using a method called Equal Channel Angular Pressing (ECAP). As the number of extrusion passes increased, the grains became smaller and more uniform. However, the process had limitations due to heat from deformation causing some grain growth. The results showed that refining the grain size improved the anode's electrochemical activity, reduced corrosion, and increased polarization and charge-transfer resistance. Tests confirmed that the anode with fine grains performed better than one with larger grains. The fine-grain structure also provided better anti-corrosion properties and enhanced battery performance in a 4 mol/L NaOH solution. At a...