Zinc Electrodes for Alkaline Storage Batteries

Battery systems of complex design and structure using—at least for one electrode—expensive materials are (for economic reasons) mainly conceived as storage batteries. Primary (and reserve ) versions of the zinc/silver oxide battery [(-) Zn/KOH/AgO (-l-)l — as a first example—are only used in particular ca.ses where the question of cost is not crucial, e.g., for marine [26-28] and space applications [29]. 

The other example, called the nickel/ zinc battery [(-Zn)/KOH/NiOOH(+)], has attracted more attention in two different versions from the application and cell design viewpoints one is the small cylindrical consumer cell [30], the other one is the flat-plate module for electrotraction [31]. A very interesting review with an extended collection of references was pub- 

Usually, this phenomenon limits the lifetime of a battery because the storage capacity falls below a reasonable lower limit. One reason for this zinc migration was identified by McBreen [35] an inhomogeneous current distribution makes the zinc move away from high current density areas. Another mechanism seems to be active as well an electrolyte convection induced by electro-osmosis through the separator [36]. 

The consequences of shape change are densification and loss of electrode porosity, increased current density caused by loss of zinc surface area, and finally earlier passivation. Two different forms of pasi-vation can stop the discharge of a zinc electrode before the active material is ex-hau.sted. Spontaneous passivation occurs 

In rechargeable nickel/zinc and sil-ver/zinc batteries this problem is partly compensated for by provision of a massive zinc reserve. The ceils are cathode-limited and the amount of anode material exceeds the theoretically required mass by a factor between two and three. 

The consequences of shape change are densification and loss of electrode porosity, increased current density caused by loss of zinc surface area, and finally earlier passivation. 

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It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

A lead-acid storage battery is only one type of battery, however. Different batteries use different metals and electrolytes to make them work. For example, alkaline batteries (the ones found in flashlights, toys, and portable electronic devices) contain powdered zinc and manganese dioxide as their electrodes. They use an electrolyte made of an alkaline solution of potassium hydroxide. Most alkaline batteries have a finite amount of chemicals in them. Once the chemicals react with one another, they are used up, and the battery goes dead (is discharged) and cannot be recharged. 

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