Issues
Aluminium as a "fuel" for vehicles has been studied by Yang and Knickle.[1] In 2002, they concluded:
The Al/air battery system can generate enough energy and power for driving ranges and acceleration similar to gasoline powered cars...the cost of aluminium 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.
Technical problems remain to be solved to make Al–air batteries suitable for electric vehicles. Anodes made of pure aluminium are corroded by the electrolyte, so the aluminium is usually alloyed with tin or other 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 being addressed in the development work on Al–air cells. For example, additives that form the alumina as a powder rather than a gel have been developed.
Modern air cathodes consist of a reactive layer of carbon with a nickel-grid current collector, a catalyst (e.g., cobalt), and a porous hydrophobic PTFE film that prevents electrolyte leakage. The oxygen in the air passes through the PTFE then 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,[9] because the aluminium reacted with the electrolyte and produced hydrogen when the battery was not in use; 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 and as backup power sources.
Another problem is the cost of materials that need to be added to the battery to avoid power dropping. Aluminium is still very cheap compared to other elements used to build batteries. Aluminium costs $2.55 per kilogram while lithium and nickel cost $15.75 and $18.75 per kilogram respectively. However, one other element typically used in aluminium air as a catalyst in the cathode is silver, which costs about $773 per kilogram (2021 prices).[10]
Aluminium–air batteries may become an effective solution for marine applications due to their high energy density, low cost, and the abundance of aluminium, with no emissions at the point of use in boats and ships.
AlumaPower,[11] Phinergy Marine,[12] Log 9 Materials, RiAlAiR[13] and several other commercial companies are working on commercial and military applications in the marine environment.
Research and development is taking place on alternative, safer, and higher performance electrolytes such as organic solvents and ionic liquids.[8] Others such as AlumaPower are focusing on mechanical methods to mitigate many of the historical issues with Al-air batteries. AlumaPower's patent (US US10978758B2) illustrates a method that rotates the anode which eliminates wear patterns and corrosion of the anode. The patent further claims that the design can use any scrap aluminium, including remelted soda cans and engine blocks.