All About Metal-Air Batteries

Highlights :

  • Even as Lithium batteries dominate the storage space for now, the search for alternatives is moving quickly, with strong backing.
  • We look at air batteries, which offer a cheaper supply chain, even as efficiencies have to catch up.

Metal-air batteries are an attractive technology. They are safer and have a higher energy density than other types of batteries. The application of air as a cathode helps in lowering the cost and the weight considerably. The utilization of cheap metals as an anode further assists in lowering the cost.

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A metal-air battery functions in an open system. This system comprises a porous air cathode, a metal anode and an electrolyte. Air cathodes utilize their oxygen. Metal anodes include zinc, lithium, aluminium and iron. There are many types of electrolytes available. These are aqueous electrolytes, aprotic electrolytes, solid state electrolytes and hybrid electrolytes.

The fundamental working principle of a metal-air battery is to electrochemically reduce the oxygen from the air and oxidize the metal. This forms solid metal oxides that may be recycled. This method allows for substantial reductions in the size and the weight of the battery.

Discharging of metal-air batteries involves a few steps. Metal changes into ions on the anodic electrode while oxygen transforms into hydroxide ions at the cathodic electrode. The diffusion of oxygen into the metal-air battery occurs through a layer known as the gas diffusion layer. During the transition of metal into metallic ions, electrons are produced. Metallic ions subsequently dissolve into the electrolyte.

All of these steps are reversed during charging of metal-air batteries.

Iron-air batteries – Iron-air batteries are a promising technology. The main resources are rust and air. Both of them are abundant, inexpensive and harmless. However, its limitation also comes from the materials used. Rapid sintering and pulverization of rust limits the ability to achieve a high number of cycles which results in diminished capacity.

Iron-air batteries could be used to store energy from photovoltaic panels, wind turbines and so on.

QuantumScape, Volkswagen AG and Form Energy are some of the major companies developing iron-air battery technology.


Aluminium-air batteries – Aluminium-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. This is because aluminium anodes are expensive and byproducts are costly to remove.

Aluminium-air batteries are not rechargeable. They will no longer produce electricity once the aluminium of anode is consumed by its reaction with the oxygen of cathode immersed in an aqueous electrolyte to form hydrated aluminium oxide. However, it is possible to mechanically recharge the battery with new aluminium anodes made from recycling the hydrated aluminium oxide.

Applications of aluminium-air batteries are restricted chiefly in military functions. Their use in vehicles is under research.

Phinergy, Fuji Pigment and Xinjiang are some of the major companies manufacturing aluminium-air batteries. Log 9 materials is an Indian startup making progress here.


Zinc-air batteries – Zinc-air batteries are powered by oxidizing zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce.

Zinc-air batteries are of various sizes. Small batteries are used for hearing aids, middling batteries are used in film cameras and large batteries are used for electric vehicle propulsion.

Some of the major companies present in the zinc-air battery market are Phinergy, Primus Power and Eos Energy Storage.


Lithium-air batteries – Lithium-air batteries use oxidation of lithium at the anode and reduction of oxygen at the cathode to produce electricity. Theoretically, lithium-air batteries can be batteries with the highest possible specific energy. However, the practical power and life of lithium-air batteries need significant improvements before they can find a market niche.

A major market driver for lithium-air batteries is the automotive sector. The energy density of gasoline is about 13 kWh/kg and that of lithium-air batteries is about 12 kWh/kg. Therefore lithium-air batteries can be a viable alternative to gasoline.

Some of the major companies present in the lithium-air battery market are Polyplus Battery Company, Mullen Technologies and Lithium Air Industries.

Comparison of Air Batteries

Applications of metal-air batteries –


  1. Metal-air batteries can be used as small power sources for portable electronic devices like electric cars.
  2. Metal-air batteries can be used as energy storage devices or as effective stations of energy transfer for renewable energy producers. This is because they can control the flow of energy from sources such as photovoltaic panels, wind turbines and so on.
  3. Metal-air batteries can be used in the treatment of water. The studies on the treatment of water conducted by metal-air batteries may be classified into three categories. These are the collection of compounds in water, the removal of heavy metals from water and the treatment of household sewage. The studies on metal-air batteries in this area are highly limited and very uncommon.
  4. Metal-air batteries hold tremendous prospects for the desalination of water. A metal-air desalination battery is a self-powered device. It can desalinate water while also generating energy.

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