Lithium/sulphur dioxide batteries

Typical voltage characteristics on medium load for a lithium type (lithium-sulphur dioxide) battery is compared with those for other types of primary battery in Figure 9.4. The outstandingly higher voltage of the lithium system is apparent. 

The lithium-sulphur dioxide battery has a high power density and is capable of delivering its energy at high current or power levels, well beyond the capability of conventional primary batteries. It also has a flat discharge characteristic. 

Figure24.7 Honeywell lithium-sulphur dioxide battery 20Ah reserve battery components (Courtesy of Honeywell)...

Nominal voltages are 1.6 V for the first step and 1.2 V for the second step. Lithium-iron disulphide batteries are usually only discharged to the end of the first step, i.e. at 1.6 V, giving a specific energy density of 640Wh/kg compared to 250Wli/Kg for the lead acid battery and 1200Wh/Kg for the lithium-sulphur dioxide battery. 

Figures 30.17 and 30.18 compare typical discharge performances of a lithium-sulphur dioxide battery at -t-20°C and —30°C, showing that very low temperatures do not have any particularly adverse effect on discharge characteristics.

Performance on constant resistance load curves for lithium-sulphur dioxide batteries are given in Figure 30.31. The effect of battery temperature between —40 and -F52°C on these curves is also shown. 

Lithium-sulphur dioxide batteries have an excellent shelf life even at 71°C. Energy loss (Wh/kg) is less than 10% during 2 years storage at 71°C. 

Lithium-sulphur dioxide cells now being supplied by leading manufacturers are claimed to retain 75% of initial capacity after 5 years storage at 21°C. Corrected for sulphur dioxide leakage, true capacity loss is estimated at 6% in 5 years, or 1% per year. Capacity loss curves Tor lithium-sulphur dioxide batteries produced by Mallory are shown in Figure 30.49. For the Mallory cell approximately 80% of the nominal capacity of the battery is available after storage for 4 years at 55°C, compared with 95% when stored at 20 C (Figure 30.49). Hermetic cells retain 65% of initial capacity after 6 months at 72°C and about 50% after 12 months at 72°Cor 6 months at 87 C. 

The capacity or service life of a lithium-sulphur dioxide cell at various discharge rates and temperatures is shown in Figure 30.55. The data are normalized for one cell and presented in terms of hours of service at various discharge rates. The linear shape of these curs es, except for the fall-off at high current levels and low temperatures, is again indicative of the capability of the lithium-sulphur dioxide battery to be efficiently discharged at these extreme conditions. These data are applicable to the standard cells and can be used in several ways to calculate the performance of a given cell or to select a cell of a suitable size for a particular application. 

So far attempts to produee a reehargeable lithium-sulphur dioxide battery have been unsueeessful. 

Data on various types of lithium-sulphur dioxide batteries in the 500-30 000 mA capacity range available from Silberkraft are given in Tables 56.5 and 56.6. 

Silberkraft have recently introduced a revised G range of lithium-sulphur dioxide batteries, which are characterized by improved low-temperature dischargeability (see Table 56.7). 

Table 56.2 Honeywell lithium-sulphur dioxide batteries...

Practical open-circuit voltages of the lithium-poly carbori-mono fluoride and lithium-sulphur dioxide systems are approximately 2.8 V and 2.9 V respectively at 20°C. The high voltage means that these batteries are not interchangeable with other electrochemical systems in existing equipment, unless a dummy cell is also included. 

Three principal types of lithium organic electrolyte battery are currently available the lithium-thionyl chloride system, the lithium-vanadium pentoxide system and the lithium-sulphur dioxide system. These batteries all have high-rate capabilities. The approximate open-circuit equilibrium cell voltages for these various cathode systems and for some other systems that have been considered are shown in Table 9.2. 

Honeywell Inc. and the Mallory Battery Company in the USA have introduced lithium batteries based on the lithium-sulphur dioxide electrochemical couple. The positive active material in these batteries, liquid sulphur dioxide, is dissolved in an electrolyte of lithium bromide, acetonitrile and propylene carbonate, and is reduced at a porous carbon electrode. 

The lithium-sulphur dioxide system is versatile and relatively inexpensive. This battery has excellent storage characteristics. Honeywell claim that the batteries should store for 12 years at 20°C. The battery can be supplied either as reserve batteries with capacities between 20 and 100 Ah or as active batteries in the 0.7—20Ah range (see Table 56.2). 

As mentioned above, the lithium-sulphur dioxide system has emerged as the leading candidate among the high energy density batteries for high-rate applications. Other lithium batteries are capable of delivering... 

The voltage discharge profile of the lithium-vanadium pentoxide battery is compared with that of lithium-thionyl chloride and lithium-sulphur dioxide systems in Figure 9.5. Lithium-vanadium pentoxide systems operate satisfactorily at temperatures as low as — 55°C with efficiencies approaching 50% (Table 9.3). 

The high-rate capability of the cells is favoured by the high conductivity of the electrolyte and the small effect of temperature on the conductivity. Heat dissipation structures are recommended for lithium-sulphur dioxide cells and batteries that operate at high power levels. Lithium-sulphur dioxide cells can operate at 460W/kg while delivering lOOW/kg in suitable high-rate configurations. 

Honeywell have described their work on the development of an alternative electrolyte for a multi-cell lithium-sulphur dioxide resen e battery. In developing a multi-cell lithium reserve battery, the lithium bromide-sulphur dioxide acetonitrile electrolyte system used in their primary batteries was found to be unstable when stored by itself at high temperature - a functional capability required for all resen e applications. In addition to consumption of the oxidant sulphur dioxide in reactions causing instability, some of the products of electrolyte degradation arc solid, which would cause nrajor problems in activation. Primary active cells after storage do not undergo such degradation reactions. 

Table 24.1 Effect of electrolytesand storage conditions on discharge performance of Honeywell lithium - sulphur dioxide reserve batteries at 560 mAh... 

Mallory supply hermetically sealed lithium-sulphur dioxide organic electrolyte cells in the capacity range 1.1-lOAh with a nominal voltage of 3.00V. Further details are given in Tables 56.2 and 56.3. Discharge curves for two of these batteries are given in Figure 30.15. 

Applications for the lithium-sulphur dioxide reserve systems include underwater mine batteries and (active batteries) memory protection, manpack communicarions, life-support equipment, sonobuoys, space probes, missiles, mines, security systems, data buoys/stations, weather sondes and electronic counter measures. The non-reserve (active) systems are used for covert sensors, memory protection and weather sondes. 

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