Silver oxide cells

Fig. 16. Comparison of battery efficiency for miniature 2inc—silver oxide cells containing KOH or NaOH electrolyte (21).

The market for batteries is huge, with new types and applications being developed all the time. For example, a watch battery is a type of silver oxide cell silver in contact with silver oxide forms one half-cell while the other is zinc metal and dications. Conversely, a car battery is constructed with the two couples lead(IV) lead and lead(IV) lead(II). The electrolyte is sulphuric acid, hence this battery s popular name of lead-acid cell (see further discussion on p. 347). 

The main features of zinc-silver oxide cells are similar to those of the zinc-mercuric oxide system, except for a higher OCV and significantly increased cost. The overall cell reaction is... 

Fig. 6.22 Discharge (a) and charge (b) characteristics of a typical 100 Ah zinc-silver oxide cell...

Fig. 6.23 Battery for Ranger lunar photography spacecraft, comprising 14 sealed 45 Ah zinc-silver oxide cells, which impacted on the moon in 1965. (By permission of Jet Propulsion Laboratory,)...

The overall cell reaction is exactly similar to the zinc-silver oxide cell, with the final discharge products being silver and Fe(OH>2. The emf of the cell is only 1.34 V, but the cell has a superior cycle life and better reliability. Batteries up to 10 kWh have been built by Westinghouse for telecommunications and submersible vehicles. 

The zinc-silver oxide cell, widely used in miniature apphcations and larger ones in mihtary apphcations, is closely... 

The main features of the zinc silver oxide cell are similar to those of the zinc mercury(II) oxide system. The principal difference apart from cost is the higher open circnit voltage the emf calculated from the standard free energies of formation of ZnO and Ag20 is 1.593 V, in close agreement with the open circuit voltage of commercial cells of 1.60 V. 

Silver oxide cells were developed in the 1960s. These cells use silver oxide mixed with carbon (to increase the electronic conductivity of the material) as cathode, amalgamated pellet zinc powder as anode, and a solution of potassium hydroxide or sodium hydroxide with dissolved zin-cates in water as electrolyte. Permion (a radiation graft of methacrylic acid onto a polyethylene membrane) is used as separator. The cell reactions are... 

Unlike some other cathode materials, such as manganese dioxide, which are quite insoluble, silver oxide has a fair degree of solubility in alkaline electrolyte. If the soluble silver species were allowed to be transported to the zinc anode it would react directly with the zinc, and as a result the cell would self-discharge. In order to prevent this from happening, zinc—silver oxide cells use special separator materials such as cellophane [9005-81-6], that are designed to inhibit migration of soluble silver to the anode. 

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