Zinc-air battery

Zinc-air battery types that are used as hearing aid batteries :
Blue (675), PR44, 11.56 mm × 5.33 mm
orange (13), PR48, 7.80 mm × 5.35 mm
brown (312), PR41 ,
7.80mm x 3.45mm Yellow (10), PR70, 5.80mm x 3.60mm

A zinc-air battery is a primary cell ; H. Disposable electric cell (colloquially mostly simply referred to as a "battery"), the voltage of which is theoretically a maximum of 1.60 V due to a zinc - oxygen reaction. The open-circuit voltage that can be achieved in practice is, however, only 1.35 to 1.4 V, since the oxygen reduction at the cathode is strongly inhibited. Zinc-air batteries are therefore in the same voltage range as the mercury oxide-zinc batteries that are no longer manufactured and have replaced them when they were used in hearing aids (see also hearing aid batteries ). The zinc-air battery was developed mainly due to the lack of raw materials after the Second World War. Today the button cell design offers the optimal power supply for analog and digital hearing aids thanks to its particularly high energy density and an almost horizontal discharge curve. It is also produced in a larger form for electric fence devices and as a lantern battery with a particularly high capacity.

After the development of highly resilient gas diffusion electrodes in foil form in the course of fuel cell development, zinc-air accumulators are also possible.

discharge

Sectional view

In the zinc-air battery, zinc is oxidized to oxide or hydroxide with atmospheric oxygen in an alkaline electrolyte , and the energy released is used electrochemically. The following reactions take place:

	equation
anode	${\displaystyle \mathrm {2\ Zn+8\ OH^{-}\to 2\ Zn(OH)_{4}^{2-}+4\ e^{-}} \quad (\mathrm {E^{0}} =-1.199\,\mathrm {V} )}$ Oxidation / electron donation
electrolyte	${\displaystyle \mathrm {2\ Zn(OH)_{4}^{2-}\to 2\ ZnO+2\ H_{2}O+4\ OH^{-}} }$
cathode	${\displaystyle \mathrm {O_{2}+2\ H_{2}O+4\ e^{-}\to 4\ OH^{-}} \quad (\mathrm {E^{0}} =0.401\,\mathrm {V} )}$ Reduction / electron uptake
Overall response	${\displaystyle \mathrm {2\ Zn+O_{2}+2\ H_{2}O\to 2\ Zn(OH)_{2}} \quad (\Delta U=1.6\,\mathrm {V} )}$ Redox reaction / cell reaction

The pores of the gas diffusion electrode must be wetted with an electrolyte in order to offer a large reaction surface for the oxygen turnover at the three-phase boundary. The "heart" of the gas diffusion electrode is an approximately 1 mm thin active layer, which has a conductive carrier material made of finely divided carbon, to which a catalyst is applied on the electrolyte side to accelerate the oxygen reduction and hydroxide oxidation.

In new batteries, the inlet opening for the oxygen in the air is usually sealed with a tab, so that the redox reactions only start when this seal is removed. Zinc-air batteries therefore have a long shelf life, but usually have to be used up within a few weeks after the seal has been removed.

charge

	equation
anode	${\displaystyle \mathrm {4\ OH^{-}\to O_{2}+2\ H_{2}O+4e^{-}} }$ Oxidation / electron donation
cathode	${\displaystyle \mathrm {2\ ZnO+2\ H_{2}O+4\ e^{-}\to 2\ Zn+4\ OH^{-}} }$ Reduction / electron uptake
Overall response	${\displaystyle \mathrm {2\ Zn(OH)_{2}\to 2\ Zn+O_{2}+2\ H_{2}O} }$ Redox reaction / cell reaction

A rechargeability can be achieved if the converted metal is mechanically replaced, which is a variant of a fuel cell with solid fuel. Such systems have been tested for their suitability in electric vehicles since the 1970s, but have not yet proven themselves.

Electric recharging would be less complex and therefore more user-friendly. The zinc electrode can be recharged in an aqueous alkaline electrolyte; however, dendrites are formed in the process , which lead to short circuits. In addition, a bifunctional, porous gas diffusion electrode must be used. Bifunctional means that it must be capable of reducing the oxygen in the air and of oxidizing the discharge product (OH ^- ) at the three-phase boundary between the solid electrode - liquid electrolyte - gas space.

Designs

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

Number / type	Color scheme	IEC (zinc-air)	ANSI (zinc-air)	Renata	Varta	Duracell	Diameter / height	Capacity (reference value)	tension
675	blue	PR44	7003ZD	ZA675	V675A	DA675	11.56 mm x 5.33 mm	600 mAh	1.4V
13	orange	PR48	7000ZD	ZA13	V13A	DA13	7.80 mm x 5.35 mm	290 mAh	1.4V
312	brown	PR41	7002ZD	ZA312	V312A	DA312	7.80 mm x 3.45 mm	160 mAh	1.4V
10	yellow	PR70	7005ZD	ZA10	V10A	DA230	5.80 mm x 3.60 mm	90 mAh	1.4V
5	red	PR63		ZA5			5.80 mm x 2.16 mm	35 mAh	1.4V

literature

• Carl H. Hamann, Wolf Vielstich: Electrochemistry. 3rd, completely revised edition. WILEY-VCH Verlag GmbH, Weinheim 1998, ISBN 3-527-27894-X .

Web links

• Spiegel Online Report on Improved Zinc Air Batteries , accessed Oct. 4, 2009
• RWE Innogy is investing 5.5 million euros in researching improved zinc-air batteries , accessed on October 4, 2009
• Explanation of the zinc-air battery
• Report in the Computerwoche about new developments regarding zinc-air batteries , accessed on November 6, 2009

Individual evidence

1. ↑ Hamann, Vielstich: Elektrochemie. 1998, p. 497.
2. ↑ Technical data sheet ( Memento of September 8, 2011 in the Internet Archive ) from Duracell.
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 77th edition. (Internet version:), CRC Press / Taylor and Francis, Boca Raton, FL, Analytical Chemistry, pp. 8-25.
4. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 77th edition. (Internet version:), CRC Press / Taylor and Francis, Boca Raton, FL, Analytical Chemistry, pp. 8-23.