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Thionyl chloride is a corrosive liquid that reacts with lithium to produce lithium chloride, sulfur and sulfur di. A carbon electrode is used as the current collector (commonly referred to as the cathode, although SOCl2 is the liquid cathode) onto which the lithium chloride precipitates. The sulfur and sulfur dioxide are soluble in the electrolyte, at lower depths of discharge. However, at high depths of discharge, SO2 causes the cell pressure to increase. Spirally wound cells are capable of high rates, especially with catalysts added to the carbon. Voltage delay is a particular problem with this system, due to incomplete passivation of the lithium surface, which can be alleviated through the use of additives. Low rate cells are now in commercial use. High rate cells have had development problems and are not widely used, mainly because of a poor shelf life and inconsistent performance. The electrolyte reacts aggressively with water.
