Metal–air electrochemical cell

Source: Wikipedia, the free encyclopedia.

A metal–air electrochemical cell is an

aprotic electrolyte.[1][2]

During discharging of a metal–air electrochemical cell, a

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.[3][4]

Types by anode element

Lithium

Main article: Lithium–air battery

The remarkably high energy density of lithium metal (up to 3458 Wh/kg) inspired the design of lithium–air batteries. A lithium–air battery consists of a solid lithium electrode, an electrolyte surrounding this electrode, and an ambient air electrode containing oxygen. Current lithium–air batteries can be divided into four subcategories based on the electrolyte used and the subsequent electrochemical cell architecture. These electrolyte categories are aprotic, aqueous, mixed aqueous/aprotic, and solid state, all of which offer their own distinct advantages and disadvantages.[5] Nonetheless, efficiency of lithium–air batteries is still limited by incomplete discharge at the cathode, charging overpotential exceeding discharge overpotential, and component stability.[6] During discharge of lithium–air batteries, the superoxide ion (O2−) formed will react with the electrolyte or other cell components and will prevent the battery from being rechargeable.[7]

Sodium

Sodium–air batteries were proposed with the hopes of overcoming the battery instability associated with superoxide in lithium–air batteries.

DMSO electrolyte was stabilized with sodium trifluoromethanesulfonimide, the highest cycling stability of a sodium–air battery was obtained (150 cycles).[9]

Potassium

Potassium–air batteries were also proposed with the hopes of overcoming the battery instability associated with superoxide in lithium–air batteries. While only two to three charge-discharge cycles have ever been achieved with potassium–air batteries, they do offer an exceptionally low overpotential difference of only 50 mV.[10]

Zinc

Main article: Zinc–air battery

Zinc–air batteries are used for hearing aids and film cameras.

Magnesium

A variety of metal–air

Magnesium–air fuel cell

Calcium

Calcium–air(O2) batteries have been reported.[15][16]

Aluminium

Main article: Aluminium–air battery

Aluminium–air batteries have the highest energy density of any other battery, with a theoretical maximum energy density of 6–8 kWh/kg, however, as of 2003, a maximum of only 1.3 kWh/kg has been achieved. Aluminium battery cells are not rechargeable, so new aluminium anodes must be installed to continue getting power from the battery, which makes them expensive to use and limited to mostly military applications.[17]

Aluminium–air batteries have been used for prototypes of electric cars, with one claiming 2000 km of range on a single charge, however none have been available to the public. However, aluminium–air batteries maintain a stable voltage and power output until they run out of power, which could make them useful for electric planes, where full power is always required in case of emergency landings. Due to not having to carry a separate metal anode, the natural low density of aluminium, and the high energy density of aluminium–air batteries, the batteries are very lightweight, which is also beneficial for electric aviation. The scale of airports could also allow for on-site recycling of anodes, which would not be feasible for cars where many small stations are necessary.[18]

Aluminium–air batteries are better for the environment compared to traditional lithium-ion batteries. Aluminium is the most abundant metal in the Earth's crust, so mines would not have to be as invasive to find a similar amount of aluminium compared to lithium. Another factor is that aluminium recycling plants already exist, while lithium recycling plants are just starting to emerge and become profitable. Aluminium is a lot more economical to recycle with current technology.[18]

Iron

Iron–air rechargeable batteries are an attractive technology with the potential of grid-scale energy storage. 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.[21] Furthermore, this technology has minimal environmental impact, as it could be used to store energy from intermittent or variable energy sources, such as solar and wind, developing an energy system with low carbon dioxide emissions.

One way the system can start is by using the Fe/FeO redox reaction. Hydrogen created during the oxidation of iron and of oxygen from the air can be consumed by a fuel cell to create electricity. When electricity must be stored, hydrogen generated from water by operating the fuel cell in reverse is consumed during the reduction of the iron oxide to metallic iron.[20][21] The combination of both of these cycles is what makes the system operate as an iron–air rechargeable battery.

Limitations of this technology come from the materials used. Generally, iron oxide powder beds are selected; however, rapid sintering and pulverization of the powders limit the ability to achieve a high number of cycles, which results in diminished capacity. 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.

Comparison

Anode element Theoretical specific energy, Wh/kg
(including oxygen) 		Theoretical specific energy, Wh/kg
(excluding oxygen) 		Calculated open-circuit voltage, V
Aluminium 4300[25] 8140[26] 1.2
Germanium[citation needed] 1480 7850 1
Calcium 2990 4180 3.12
Iron 1431 2044 1.3
Lithium 5210 11140 2.91
Magnesium 2789 6462 2.93
Potassium 935[27][28] 1700[Note 1] 2.48[27][28]
Sodium 1677 2260 2.3[29][30]
Tin[31] 860 6250 0.95
Zinc[citation needed] 1090 1350 1.65

See also

Notes

  1. ^ Calculated from the specific energy density (including oxygen) value and 39.1 and 16 atomic weight data for K and O respectively for KO2

References

  1. ^ "Metal air". December 27, 2010. Archived from the original on 2010-12-27.
  2. ^ "Metal–Air Batteries Lithium, Aluminum, Zinc, and Carbon" (PDF). Retrieved 2013-04-04.
  3. OSTI 1373737
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  4. doi:10.1016/j.gee.2016.04.004
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  5. doi:10.1021/jz1005384
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  6. doi:10.1016/j.jpowsour.2010.09.031
    .
  7. ^ Zyga, Lisa. "Sodium–air battery offers rechargeable advantages compared to Li–air batteries". Phys.org. Retrieved 1 March 2018.
  8. PMID 23202372
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  9. PMID 27809386
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  10. PMID 23402300
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  11. ISSN 0013-4651
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  12. ISSN 2051-6347
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  13. ISSN 2211-2855
    .
  14. ^
    S2CID 102825802
    .
  15. ISSN 2050-7496
    .
  16. ISSN 1932-7447
    .
  17. ISSN 0378-7753
    .
  18. ^ a b "Can Aluminium–air batteries outperform Li-ion for EVs?". Energy Post. 2021-09-08. Retrieved 2023-01-08.
  19. doi:10.1016/j.ssi.2011.12.002
    .
  20. ^
    S2CID 93103339
    .
  21. ^
    doi:10.1016/j.jpowsour.2011.03.086
    .
  22. S2CID 15711041
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  23. doi:10.1016/j.matlet.2014.11.155
    .
  24. doi:10.1016/j.ijhydene.2016.06.062
    .
  25. ^ "Electrically Rechargeable Metal–Air Batteries (ERMAB)". Archived from the original on 3 March 2016. Retrieved 25 March 2012.
  26. ^ "Batteries for Oxygen Concentrators". NASA.gov. Archived from the original on 26 February 2014.
  27. ^
    PMID 23402300
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  28. ^
    PMID 23402300
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  29. doi:10.1016/j.elecom.2011.12.019
    .
  30. ^ "BASF investigating sodium–air batteries as alternative to Li–air; patent application filed with USPTO". Green Car Congress.
  31. doi:10.1016/j.jechem.2015.08.006
    .

External links
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