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 TM 9-8000
and extensive testing for tank-automotive applications.
the trivalent nickel hydroxide Ni(OH)3 is converted to the
This battery employs nickel and cadmium compounds as
divalent hydroxide Ni(OH)2 at the positive plate with the
the active material and potassium hydroxide as
reverse process occurring during charging. The negative
electrolyte. There are actually two basic types of nickel-
plate consists of metallic cadmium when fully charged.
cadmium batteries. These are distinguished by the
This is converted to the hydroxide during discharge and
method used to construct the plates. One is called a
back to metallic cadmium during charging.
pocket plate and the other a sintered-plate design. In
c. Features.
addition, the nickel-cadmium battery is produced with
both vented cells and completely sealed cells. The
vented sintered-plate, nickel-cadmium battery is the one
(1) The low internal resistance of the
most often used in military applications because it offers
sintered-plate battery makes it ideal for service requiring
high discharge rates at wider temperature ranges. For
long battery life and high current drains over a wide
this reason, the discussion of the nickel-cadmium battery
temperature range.
will be confined largely to the sintered-plate version. The
basic difference between the pocket and sintered plate is
(2)
The sintered-plate construction of the
that, in the pocket type, the active material of the plates
positive and negative electrode allows plates to be
is encased within perforated steel pockets, while the
constructed as thin as 0.02 inch. This allows more
sintered type has the active material contained in a
plates to be installed in a given size cell with less space
sintered structure surrounding the grid. Although the
between plates. The internal resistance of the sintered-
sintered method is more expensive per ampere-hour
plate cell is thus about one-half that of a pocket plate
than the pocket plate type, superior performance at high
type.
rates and reduced capacity loss at low temperatures
qualify it as the logical choice for military applications.
(3) The specific gravity of the potassium
hydroxide electrolyte does not change during charge or
b. Construction.
discharge. This is because the electrolyte does not enter
into the chemical reaction between the positive and
(1) The sintered plate consists of three
negative electrodes, as does sulfuric acid in the lead acid
components. One is the metal grid that acts as the
battery. For this reason, specific gravity readings of the
current collector. This grid is constructed either of pure
nickel-cadmium electrolyte are not an indication of the
nickel, a woven screen of nickel-plated steel, expanded
state-of-charge. The open circuit voltage of a charged
metal, or perforated sheet. The second component is a
nickel-cadmium cell is about 1.3 volts, and the average
fine nickel powder that is sintered on the grid and has a
and final discharge voltages at normal rates of discharge
porosity of approximately 80 percent.
The third
are about 1.2 and 1.1 volts, respectively.
component is the active material that is impregnated in
the pores of the sintered powder. A nickel salt is used
(4) The fact that the electrolyte serves virtually
for the active material in the positive plate, and a
as a conductor offers several advantages. One is that
cadmium salt for the negative.
very little gassing occurs on charging, except when
overcharged, and none on -discharge. Therefore, little
(2) Once the plates are constructed, they are
water is lost. Another is that the rate of self-discharge is
formed into cell elements similar to the lead-acid battery.
very low. Thus, the battery may be left standing on open
The plates are isolated from one another with nylon-
circuit for periods up to a year and still retain as much as
cellophane type separators and placed into a container
70 percent of its original charge. Still another advantage
usually of high-impact plastic.
of the nickel-cadmium battery is that it will accept a
charge at a temperature as low as -40F, by virtue of
(3) The positive plate of the nickel-cadmium
self-heating. At temperatures below -40F, however, the
battery is made up of Ni(OH)3 and Ni(OH)2 whereas the
electrolyte forms a slush that does slow down chemical
negative consists of Cd and Cd(OH)2. During discharge,
reactions.
12-7
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