Page 355 - Lindens Handbook of Batteries

14.20 PriMAry BATTerieS

Discharge. Typical discharge curves for the standard-rate Li/SO battery at 20°C are given
2
in Fig. 14.9a. The high cell voltages and the flat discharge profile are characteristic of the Li/SO
2
battery. Another unique feature is the ability of the Li/SO battery to be efficiently discharged over
2
a wide range of current or power levels, from high-rate short-term or pulse loads to low-drain continuous
discharges for periods of 5 years or longer. At least 90% of the battery’s rated capacity may be
expected on the long-term discharges. Figure 14.9b shows the discharge curves for a high-rate D-size
battery at four rates up to 3 A.
The Li/SO battery is capable of higher-rate discharges on pulse loads. For example, a squat
2
D cell designed in a high-rate construction can deliver pulse loads as high as 37.5 A, producing
17
59 watts of power. For high-rate designs, extended discharges, however, at rates above the 2 h
rate may cause overheating. The actual heat rise depends on the battery design, type of discharge,
temperature, and voltage. As discussed in Sec. 14.4, the design and use of the battery should be
controlled to avoid overheating.
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A study has shown that the high-rate pulse output of the lithium/sulfur dioxide battery
may be enhanced by a variety of design variables. Multiple tabbing (1 to 3) of both anode and
cathode, optimizing the composition of the cathode mix and reducing the aspect ration (length/
width) of the electrodes were all found to reduce polarization during high-rate, 10 s pulse
discharge. D-size cells and thin D-size cells (1.1 in diameter × 2.20 in high) with anodes and
cathodes containing 2 tabs using an optimized cathode mix were found capable of producing
99 and 97 watts, respectively, under 50 A, 10 s pulses. Ultimately, a 5/4 C-size cell without
multiple tabbing but using the optimized cathode mix was selected for reasons of volumetric
efficiency to produce a 74-cell, 110 V battery capable of providing 5500 watt, 10 s pulses for
a U.S. Navy application.
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A similar design optimization study has resulted in the production of a Li/SO D-cell with a
2
room-temperature capacity of 9.1 Ah at 250 mA and 8.8 Ah at 2 A. This compares to 7.75 Ah for the
standard design and was achieved through an optimization study in which the aspect ratios of both
anode and cathode were varied along with the use of three types of carbon in the cathode and the
use of a central cathode tab. When discharged between 2.0 and 0.0 V, these cells were found to gen-
erate less heat than the standard cells. The high-capacity cells were used to construct U.S. Military
BA-5590 batteries, which were tested to the requirements of MiL-PrF-49471. These batteries met
the specification requirements for performance and safety.
Effect of Temperature. The Li/SO battery is noted for its ability to perform over a wide
2
temperature range, from -40 to 55°C. Discharge curves for a standard-rate Li/SO battery at
2
various temperatures are shown in Fig. 14.10. Significant, again, are the flat discharge curves
over a wide temperature range, the good voltage regulation, and the high percentage of the
20°C performance available at the temperature extremes. As with all battery systems, the rela-
tive performance of the Li/SO battery is dependent on the rate of discharge. in Fig. 14.11,
2
the discharge performance of a standard-rate cell is plotted as a function of load and battery
temperature.
Internal Resistance and Discharge Voltage. The Li/SO battery has a relatively low internal
2
resistance (about one-tenth that of conventional primary batteries) and good voltage regulation
over a wide range of discharge loads and temperatures. The midprint voltage of the discharge of a
standard-rate Li/SO battery (to an end voltage of 2 V) at various discharge rates and temperatures
2
is plotted in Fig. 14.12.
Service Life. The capacity or service life of the Li/SO battery at various discharge rates is given
2
in Fig. 14.13. The data are normalized for a 1-kg or 1-L size battery and presented in terms of hours
of service at various discharge rates. The linear shape of this curve is again indicative of the capability
of the Li/SO battery to be efficiently discharged at these extreme conditions. This data can be used
2
in several ways to calculate the approximate performance of a given battery or to select a Li/SO
2
battery of suitable size for a particular application, recognizing that the specific energy of the larger-
size batteries is higher than that of the smaller ones.