Cell reactions lithium thionyl chloride

Lithium—Thionyl Chloride Cells. Lidiium—thionyi chloride cells have very high energy density. One of the main reasons is the nature of the ceU reaction. 

When discussing cathodes for primary cells, it is important to make a distinction between solid materials, mentioned above, and those in which the cathode electrochemical component is not in the physical electrode structure, but rather exist in a liquid or gas state. Examples include zinc air cells, lithium thionyl chloride cells, and lithium sulfur dioxide cells. In each case, the physical cathode stmcture serves as a catalytic reaction... 

The reaction involves two electrons per thionyl chloride [7719-09-7] molecule (40). Also, one of the products, SO2, is a Hquid under the internal pressure of the cell, facihtating a more complete use of the reactant. Finally, no cosolvent is required for the solution, because thionyl chloride is a Hquid having only a modest vapor pressure at room temperature. The electrolyte salt most commonly used is lithium aluminum chloride [14024-11-4] LiAlCl. Initially, the sulfur product is also soluble in the electrolyte, but as the composition changes to a higher SO2 concentration and sulfur [7704-34-9] huA.ds up, a saturation point is reached and the sulfur precipitates. 

The density of sulfur is close to that of lithium chloride. The volume of solid sulfur formed in reaction (11.9) is less than 16% of the overall volume of solid products. Sulfur dioxide formed in reaction (11.9) is rather soluble in electrolyte, so that the intrinsic pressure in the cells is enhanced negligibly. Despite this, the cases of thionyl chloride-lithium cells are made to be rather strong and the extreme corrosion activity of thionyl chloride enforces application of high-alloy steels or nickel. Sintered glass-metal pressure seals are used in thionyl chloride-lithium cells, same as in cells with some other systems. 

The main current-producing reaction is described by Equation (11.11). The product of this reaction is lithium dithionite that is insoluble in the electrolyte. Therefore, a reasonable porous cathode structure is of great importance for provision of high capacity and power characteristics of sulfur dioxide-lithium cells. The cathodes in such cells are similar to cathodes of thionyl chloride-lithium cells. The cells of the "lithium-sulfur dioxide" system are also produced using the rammed and wound coil designs. Porous polypropylene is applied as a separator. 

More recently, spin-dependent liquid-electrolyte reserve batteries employing lithium anodes have been developed. The most promising system is that in which thionyl chloride serves in the dual role of electrolyte carrier and active cathodic depolarizer (see Chap. 20). The accepted cell reaction for this system is... 

The basic cell structure that is generally used for this system consists of a lithium anode, a nonwoven glass separator and a Tellon -bonded carhon cathode which serves only as the reaction site medium. One unique feature of this chemistry is the fact that thionyl chloride (SOCy serves two functions—as the solvent of the commonly used LiAlCL in SOCI2 electrolyte solution and as the active cathode material (see Sec. 14.6). 

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