[1][2] During discharging of a metal–air electrochemical cell, a reduction reaction occurs in the ambient air cathode while the metal anode is oxidized.
The specific capacity and energy density of metal–air electrochemical cells is higher than that of lithium-ion batteries, making them a prime candidate for use in electric vehicles.
While there are some commercial applications, complications associated with the metal anodes, catalysts, and electrolytes have hindered development and implementation of metal–air batteries.
These electrolyte categories are aprotic, aqueous, mixed aqueous/aprotic, and solid state, all of which offer their own distinct advantages and disadvantages.
Since NaO2 will decompose reversibly to an extent back to the elemental components, this means sodium–air batteries have some intrinsic capacity to be rechargeable.
The main raw-material of this technology is iron oxide (rust), a material that is abundant, non-toxic, inexpensive, and environmentally friendly.
[19] Most of the batteries currently being developed utilize iron oxide powders to generate and store hydrogen via the Fe/FeO reduction/oxidation (redox) reaction (Fe + H2O ⇌ FeO + H2).
[20] In conjunction with a fuel cell, this enables the system to behave as a rechargeable battery, creating H2O/H2 via the production and consumption of electricity.
Other methods currently under investigation, such as 3D printing[22] and freeze-casting,[23][24] seek to enable the creation of architecture materials to allow for high surface area and volume changes during the redox reaction.