Magnesium-air cells

MECHANICALLY RECHARGEABLE MAGNESIUM-AIR CELLS WITH N aCl-ELECTROLYTE... 

A passive film is formed on the Mg electrode surface in alkaline solutions, which creates problems when the Mg-air cell is to be discharged. However Mg and especially some Mg alloys are suitable to be used in magnesium-air cells with NaCl-electrolyte [4], where the formation of the passive film on the magnesium surface is not observed. 

The magnesium-air cells under investigation are electrochemical cells containing two air gas-diffusion electrodes (cathodes) and a magnesium anode. NaCl-solution is used as an electrolyte. 

Pyrolyzed catalysts obtained by heat treatment in Argon of active carbon impregnated with solution of the compound Co-tetramethoxyphenylporphirine (CoTMPP) are studied [9], Air gas-diffusion electrodes with this catalyst show low polarisation in a wide interval of current densities (up to 100 mA/cm2) and stable long-term performance. These catalysts are more suitable for use in magnesium-air cells operating at high current drains, but unfortunately their price is comparatively high. 

Sheets of magnesium or magnesium alloys were used as anodes in the developed magnesium-air cells. 

Several types of experimental magnesium-air cells were tested. These cells varied in their size (the working area of the air electrodes used) [10]. The current-voltage curves of an experimental Mg-air cell with two air electrodes (Sair = 80 cm2) with pyrolyzed CoTMPP catalyst and sandwich-type Mg anode (MA8M06) operating in NaCl-electrolytes with different concentrations are presented by Figure 2. 

The testing of the different magnesium anodes is performed in magnesium-air cells with two air electrodes with pyrolyzed CoTMPP catalyst (S = 65 cm2). One-sheet Mg anodes were used in 4N NaCl media. 

The comparison of the data from Figure 4 shows that the pure magnesium (99.99%) is the most suitable material to be used as anode in magnesium-air cells with NaCl-electrolyte. The magnesium alloy type... 

In Figure 5 we compare the discharge curves at a constant load of 0,6 Q of similar magnesium-air cells with anodes from Mg 99.99% and from Mg-alloy MA8M06. 

Mechanically rechargeable magnesium-air cells were designed and investigated. The most important feature of these cells is that the cell-case with the air electrodes can be used many times. 

The main advantage of the magnesium-air cells is the use of NaCl-electrolyte. This makes the magnesium-air cells environmentally friendly. They are clean, no toxic emission are produced in a way that is safe for user, even for children because the NaCl-electrolyte is not chemically aggressive and magnesium is not toxic. The mechanical recharging of these cells can be accomplished without any chemical danger. 

Something more the magnesium-air cells possess an infinite shelf life because the electrolyte can be removed easily before storage. When power is needed, the electrolyte is poured back into the cell. No other electrochemical energy sources do exist in which the electrolyte can be removed, stored and reused by the consumer. 

From the presented results it can be concluded that the magnesium-air cells feature substantially increased power output. They can be used as primary, mechanically rechargeable and emergency energy sources for the residential, commercial and industrial markets. 

Kaisheva A., Iliev I., Milusheva J. Mechanically rechargeable magnesium-air cells with non-aggressive electrolyte. International Congress for Battery Recycling, July 3-5, 2002, Vienna, Austria. 

Several types of magnesium-air cells [16] with neutral electrolyte (NaCl solution) are also developed and investigated. 

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