Page 121 - Battery Reference Book

Nickel-cadmium secondary batteries 4/5
recharged many times. They are small convenient
packages of high energy output, hermetically sealed
in leak-resistant steel cases, and will operate in any
._ position. The cells have very low internal resistance
g 201 I
I l l I l l l I and impedance, and are rugged and highly resistance
$ 0 2 4 6 8 10 to shock and vibration. Some general comments on
Discharge current (X I,o) sealed nickel-cadmium batteries are made below.
c 100 - (a) Temperature of operation
-
-
0
e 80 i Cells and batteries may be charged, discharged and
8 60 stored over a very wide temperature range. The stated
maximum permissible temperature ranges for these
batteries are as follows:
Charge 0 to +45"C
Discharge -20 to +45"C
Storage -40 to +50"C
Figure 4.4 Effects of improvement in plate active materials
since the 1950s on the performance of the Varta 0.225Ah Discharge and storage at +60T are permissible for a
nickel-cadmium sealed battery: available capacity at 20°C
(a) before and (b) after improved materials were incorporated maximum of 24 h (see also Table 4.3).
(Courtesy of Varta) Use at high temperatures, however, or charging
at higher than recommended rates, or repeated dis-
charge beyond the normal cut-offs, may be harmful.
high discharge rates, therefore the discharge voltage is In the case of button cells which do not contain a
not indicative of the cell's state of charge. At rates of safety vent, charging at temperatures lower than those
discharge up to ten times the 110 rate, a cell is said recommended may cause swelling or cell rupture.
to be fully discharged at 0.9V. The voltage of a cell For low-temperature operation (0°C or below), sin-
when discharged below 0.9 V falls rapidly to zero and tered cells are recommended. At these temperatures,
it is therefore possible for some cells in a battery to the cell's internal resistance increases and this can
reverse their polarity. Provided the discharge rate is greatly affect the voltage characteristic at high dis-
at the II0 rate or less, this reversal will not harm the charge rates. The low temperature charge problems
nickel-cadmium cell, but with maximum life in view of sealed nickel-cadmium cells are caused partly by
it should be avoided. the poor charge efficiency of the negative electrode
Sealed nickel-cadmium cells and batteries exhibit at these temperatures. Also, at low temperatures, the
relatively constant discharge voltages. They can be cell's ability to recombine oxygen during overcharge

Table 4.3 Effect of high and low temperatures on storage, discharging and charging of Eveready nickel-cadmium cells and b- dieries
Low temperature High temperature

Storage (all types) At -40°C At 60°C
No detrimental effect. However, cells or No detrimental effect. However, self-discharge
batteries should be allowed to return to is more rapid starting at 32°C and
room temperature prior to charging increases as temperature is further elevated
Discharge (all types) At -20°C At 45°C
No detrimental effect, but capacity will be No detrimental effect
reduced as shown by curves
Charge CF and CH At 0°C At 45°C
types (10 h rate) Cells or batteries should not be charged Cells or batteries show charge acceptance
below 0°C at the 10h rate of approximately 50%
CF types (1-3 h rate) At 15.6"C At 45°C
Cells or batteries should not be charged Cells or batteries show charge acceptance
below 15.6"C at the 1 h rate or below 10°C of approximately 90%
at the 3 h rate
Button cells At 0°C At 45°C
Cells or batteries should not be charged Cells or batteries show charge acceptance
below 0°C at the 10h rate of approximately 60%. Also possible
detrimental effect on cycle life