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Lithium-Sulfur Dioxide Battery

These cells are utilized for military applications and some industrial applications. They are also used in automated external defibrillators ("AEDs") that can restore a normal heart rhythm to victims of sudden cardiac arrest.

This EPS has a very high energy density and particularly good for low temperature and high current delivery. The construction of the Li/SO2 cell is typically cylindrical. The nominal voltage is usually specified at 3V, while the typical working voltage ranges around 2.8V. The discharge curve is extremely flat. Shelf life is good at even high temperatures and about 10 years at normal and cooler temperatures. After extended shelf storage times, the lithium anode may start to form a protective film. This film will initially cause a voltage delay when first placed into service. The duration of this delay will largely depend upon the temperature, storage time, and discharge current, ranging from fractions of a second to many seconds.

This system is now in widespread use in the military with radio packs and other communication equipment. Sulfur di is a gas at normal temperatures but, in the cells, it is dissolved in an organic solvent. The fresh cells have an internal pressure of 2 to 3 atmospheres, which decreases as the SO2 is consumed during discharging. An important property of Li/SO2 cells is that they operate efficiently at -40C. Although Li/SO2 cells have gained acceptance, they may be displaced by lithium-manganese dioxide batteries for applications where the temperature does not go below -20oC. This latter system is not pressurized.

In bobbin cells, the lithium anode forms a tube around the central carbon cylinder. The surface area of the electrode of these cells ranges from 4 to 100 sq. cm., which provides maximum capacity. However, current flows do not exceed a few hundred milliamps.

In spiral cells, the lithium and carbon electrodes are wound together. The electrode surface can therefore be as high as several hundred sq. cm. Because of this, spiral cells provide instant current flows of up to several amps, as against tens of milliamps for a bobbin battery of the same size.

Li-SO2 cells use a lithium anode and a porous carbon electrode to catalyze the reaction of the SO2 (the active cathode material). Since there is a liquid cathode, the main chemical reactions are the same as those for Li-SOCl2 cells, in particular with the formation of a protective layer at the interface of the lithium and the SO2. Li-SO2 cells internal pressure is 3 bars (300 kPa), at +20C and 14 bars (1400 kPa), at +70C, so as to maintain the SO2 in a liquid form. This is a positive safety feature of LiSO2 because in the event of a vent occurs, the electrolyte leaves the cell and shuts down any other reactions.

Chemical reaction2Li + 2 SO2 --> Li2 S2O4