Page 255 - Handbook of Battery Materials

8.3 Battery Anodes (‘Negatives’) 225

Table 8.1 Open circuit voltages of battery systems with zinc anodes.

Open circuit voltage (V) Cathode material

1.6 MnO 2 ,acidic
1.5 MnO 2 , alkaline
1.73 NiOOH
1.85 AgO
1.65 O 2 /air
2.12 Cl 2
1.85 Br 2
1.84 K 3 [Fe(CN) 6 ]

8.3.7
Zinc (Zn)

The zinc electrode is probably the most widely used metallic negative. The material
−1
is relatively cheap, has a good electrochemical equivalent (820 Ah kg ), and shows
high OCVs in most systems (Table 8.1).
It is so universally applied that it may be found in combination with metal
oxide cathodes (e.g., HgO, AgO, NiOOH, MnO 2 ), with catalytically active oxygen
electrodes, with inert cathodes using aqueous halide or ferricyanide solutions
as active materials (‘zinc-flow’ or ‘redox’ batteries), and with reducible organic
materials on metal carriers [119–121].
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 for 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:

Zn ←→ Zn 2+ + 2e − (8.18)

This reaction may be followed by other (complex formation and/or precipitation)
reactions which are independent of the electrode potential but determined by the
nature and concentration of the electrolyte.
It is impossible to discuss all the problems related to zinc electrodes with-
out looking at the electrolyte system and the kind of cell operation (primary
or rechargeable). The only way to cover all the possible combinations is an-
other mode of characterization or categorization, which is used in the subse-
quent sections: Sections 8.3.7.1, [(−) Zn/NH 4 Cl, ZnCl 2 /MnO 2 (+)]; 8.3.7.2, [(−)
Zn/KOH/HgO, MnO 2 ,air (+)]; 8.3.7.3, [(−) Zn/KOH/NiOOH, AgO (+)]; 8.3.7.4,
[(−) Zn/KOH/MnO 2 ,air (+)]; 8.3.7.5, [(−)Zn/H or OH /Br 2 ,Cl 2 , ferricyanide
−
+
(+)]; and 8.3.7.6.