Page 252 - Lindens Handbook of Batteries

10.4 priMAry bATTerieS

10.2.1 Aluminum
The standard potential for aluminum in the anode reaction,

3+
Al → Al + 3e
is reported as -1.7 V. A battery with an aluminum anode should have a voltage about 0.9 V higher
than the corresponding zinc battery. However, this voltage is not attained, and the voltage of an Al/
MnO battery is only about 0.1 to 0.2 V higher than that of a zinc battery. The Al/MnO battery
2
2
never progressed beyond the experimental stage because of the problems with the oxide film, exces-
sive corrosion when the film was broken, voltage delay, and the tendency for aluminum to corrode
unevenly. The experimental batteries that were fabricated used a two-layer aluminum anode (to
minimize premature failure due to can perforation), an electrolyte of aluminum or chromium chlo-
ride, and a manganese dioxide-acetylene black cathode similar to the conventional zinc/manganese
dioxide battery. The reaction mechanism is
Al + 3MnO + 3H O → 3MnO · OH + Al(OH) 3
2
2
10.3 CONSTRUCTION OF Mg/MnO BATTERIES
2

Magnesium/manganese dioxide (nonreserve) primary batteries are generally constructed in a cylin-
drical configuration.

10.3.1 Standard Construction
The construction of the magnesium battery is similar to the cylindrical zinc-carbon battery.
A cross section of a typical battery is shown in Fig. 10.3. A magnesium alloy can, containing
small amounts of aluminum and zinc, is used in place of the zinc can. The cathode consists of

Carbon pencil cap Plastic seal washer

Retainer ring
Compression washer
Cathode mix

Carbon pencil
Magnesium can
Separator
Bottom cup

FIGURE 10.3 Cylindrical construction of magnesium primary battery.