Zinc–air battery

A zinc -air battery is a primary cell, i.e. electric disposable cell ( colloquially often referred to simply as "Battery" ), created the theoretical maximum voltage of 1.60 V due to a zinc - oxygen reaction. However, practically achievable load voltage is as low as 1.35 to 1.4 V, because the reduction of oxygen is strongly inhibited in the cathode. So are zinc -air batteries in the same voltage range as the no longer manufactured mercury - zinc batteries and have this in the application in hearing aids (see also hearing aid battery ) replaced. The zinc -air battery was developed primarily due to the lack of raw materials after the Second World War. Today it offers in the design of a button cell with particularly high energy density and an approximately horizontal discharge curve, the optimal power supply for analog and digital hearing aids.

After heavy-duty gas diffusion electrodes are formed in a sheet form in the course of development of fuel cells, zinc air batteries are possible.

Discharge

In the zinc - air battery Zinc metal is oxidized by atmospheric oxygen in an alkaline electrolyte to the oxide or hydroxide and used the thus liberated energy electrochemically. It run the following reactions take place:

A rechargeability can be achieved when the unreacted metal is mechanically replaced, thus a variation of a fuel cell with solid fuel is present. Such systems are tested for their suitability in electric vehicles since the 1970s, but have not been able to prove.

An electric recharge would be less complex and therefore more user friendly. Recharging of the zinc electrode is also possible, in an aqueous alkaline electrolyte; but this form dendrites that lead to short circuits. In addition, a bifunctional porous gas diffusion electrode to be used. Bifunctional means that they for the reduction of atmospheric oxygen and the oxidation of the discharge product ( OH ) at the three phase boundary solid electrode - must be capable of headspace - liquid electrolyte.

Charge

The pores of the gas diffusion electrode to be impregnated with an electrolyte, to provide a large reaction surface for the oxygen conversion at the three phase boundary. The "core " of the gas diffusion electrode is an approximately 1 mm thin active layer, which comprises a conductive support material consists of particulate carbon, a catalyst on the electrolyte side is applied to accelerate the reduction of oxygen and Hydroxidoxidation.

In zinc -air cells about 400 to 600 are within Lade-/Entladevorgänge; the average discharge voltage is about 1.16 V.

With new batteries, the inlet for the oxygen in the air is usually sealed with a flap, so that the redox reactions begin only upon removal of this label. Therefore, zinc -air batteries are characterized by a long shelf life, but must be used up usually within a few weeks after removal of the seal.

Designs

The currently most common types are 13 (orange), 312 (brown) and 10 (yellow), which are used particularly in hearing aids.