Lithium sulphur cells

Fig. 4.31 Internal pressure of lithium-sulphur dioxide cells as a function of temperature. (By permission of Elsevier Sequoia D, Linden and B, McDonald, J, Power Sources, 1980,5, 35.)...

Fig. 4.33 Discharge curves for D-size lithium-sulphur dioxide cells at ambient temperature (a) 270 mA (b) 180 mA (c) 140 mA. (By permission of Elsevier Sequoia SA as Fig. 4.31.)...

The energy density of liquid cathode lithium cells can be further enhanced to over 500 Wh/kg (1000 Wh/dm3) by the use of halogen additives. BrCl, added to lithium-thionyl chloride cells, boosts the OCV to 3.9 V and prevents the formation of sulphur in the early stages of discharge. D-sized cells are manufactured, Addition of chlorine to lithium-sulphur yl chloride cells increases the energy density and improves the temperature-dependent electrical characteristics. 

If the lifetime of Li-based batteries (the term lithium ion batteries for batteries with polar Li-compounds as negative electrodes is very unfortunate) can be further enhanced, they will be also of importance for electrotraction. The classical battery type used in automobiles, viz, the lead-acid accumulator, is distinctly superior in terms of long-time stability but possesses too low an energy content per unit weight as to drive automobiles. Driving car of sensible size and performance with this alone requires a battery weight on the order of 11, (This problem is not removed by using Ni-Cd accumulators,) Much effort has been undertaken to develop a sodium-sulphur cell. In the Na-S cells ... 

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. 

The reactivity of lithium necessitates controlled-atmosphere assembly - in some cases the use of expensive materials in the cell construction to avoid corrosion, and in some cases (for example, lithium-sulphur dioxide) the provision of a sophisticated seal design. 

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. 

Figure 9.2 Comparison of energy density of lithium-sulphur and other types of cell (Courtesyof Honeywell)...

Figure9.5 Voltage discharge profile of llthlum-vanadlum pen-toxide (VzOa), lithlum-thionyl chloride (SOCIj), lithium-sulphur dioxide (SO2) lithium-molytxfenum trioxide (M0O3) cells (Courtesy of Honeywell)...

The lithium-sulphur dioxide cell has an open circuit voltage of 2.92 V at 20°C and a typical voltage under... 

Lithium-sulphur dioxide cells are available in a variety of cylindrical cell sizes from companies such as Honeywell and Duracell International, capacities available ranging from 0.45 to 21 Ah. Larger cells are under development. A number of the cells are manufactured in standard ANSI (American National Standards Institute) cell sizes in dimensions of popular conventional zinc primary cells. While these single cells may be physically interchangeable, they are not electrically interchangeable because of the high cell voltage of the lithium cell. 

This system uses a lithium anode and a gaseous cathode dissolved in an inorganic electrolyte. It has a 3.63 V open-circuit voltage and a typical voltage under rated load of 3.2-3.4V. Like the lithium-sulphur dioxide system, it has a very flat discharge profile through 90% of its life. Cell construction is similar... 

The discharge of lithium-sulphur dioxide cells is accompanied by the precipitation of lithium dithionite in the cathodes, but the precipitate appears not to lessen the rate capability of the cells noticeably. An optimal electrolyte composition can be specified that permits the cathodes to operate along a maximal conductivity path during discharge. 

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