Page 132 - Battery Reference Book

4/16 Nickel batteries

1.6
% 1.5
m
= 1.4
1.0 -
1.2
I I I I I I I
0 1 2 3 4 5 6 0 50 100 150 200 250 300 350
Capacity (A h) Capacity (A h)
(a) (b)
Figure 4.15 (a) Eagle Picher NZSL5.0 (5A h) nickel-zinc battery at 27°C (Courtesy of Eagle Picher) (b) Projected effect of discharge
temperature on a Yardney nickel-zinc cell of 300Ah capacity (Courtesy of Yardney)

in Figure 4.15(a). If the battery is operated in a cold occurs with state of charge. It should be noted, how-
climate performance is affected (Figure 4.15(b)) and a ever, that the cell pressure can increase with cycling;
cooling or heating system is required. this can cause a shift in the state of charge versus
This system has never really been commercially pressure curve. In a nickel-hydrogen cell the hydro-
successful. Despite all efforts the system is plagued gen gas is not isolated. It comes into direct contact
by poor cycle life. Even in recent trials on prototype with the nickel electrodes, resulting in a relatively
Yuasa electric vehicle batteries only 200 cycles were slow discharge on the NiOOH active electrode mass.
obtained. The rate of this reaction is dependent on temperature
and hydrogen pressure. The Spacenet battery cells on
average lose about 15.5% capacity during a 72 hour
4.4 Nickel-hydrogen secondary open circuit stand at 10°C. For a low earth orbit cycle
batteries regime the self-discharge is acceptable. For extended

Some of the advantages of the nickel-hydrogen com- storage, however, the battery should be trickle charged
pared to nickel-cadmium battery are: (a) longer cycle if a full charge is required. They are rapidly replac-
life; (b) higher specific energy; (c) inherent protection ing nickel-cadmium as the energy storage system of
against overcharge and overdischarge (reversal) and choice. In Table 4.11 characteristics are listed of three
(d) cell pressure can be used as an indication of state commercially available types of nickel-hydrogen cells
of charge. Some of the disadvantages are (a) relatively
high initial cost due to limited production, which could Table 4.1 1 Characteristics of three types of nickel-hydrogen
be offset by cycle life costs, and (b) self discharge cells and batteries
which is proportional to hydrogen pressure.
Nickel-hydrogen batteries have captured a large Spacenet Intelstat V Superbird
share of the space battery market in recent years. Comset Comset (similar to
For a representative Spacenet battery cell the dis- Design Design Airjforce Hughes
charge voltage plateau as a function of ampere-hours + Design)
removed at 0, 10, and 20°C is relatively independent ~
of temperature over the range tested. Individual cells
40
30
83
The effect of discharge rate on capacity at 10°C Rated capacity (Ah) 117 0.89 1.87
Weight (kg)
for a representative 48 ampere-hour Hughes cell is Capacity (Ah)
relatively independent of the discharge rate over the 20°C 42 32 92
range tested. In general, the charge voltage increases 0°C 50 35 -
with decreasing temperature. The pressure increases Discharge
with state of charge. The temperature effect on cell voltage (V) 1.25 1.25 1.24
pressure is minor over the range tested. Specific energy
During normal operation of a sealed rechargeable Whkg-' at 20°C 44.6 44.8 60.9
nickel-hydrogen battery cell, hydrogen is produced 27 cell batteries
during charge and consumed during discharge. The Battery weight (kg) 32.6 30.1 64.5
hydrogen pressure is proportional to the ampere-hours Energy Wh at 10°C 1328 1174 3448
into or out of the cell and can be used as an indica- Specific energy
tor of stage of charge. A linear variation of pressure Wh/kg-' at IO'C 40.7 39 53