Abstract: A method of preventing overpressurization of a lithium-thionyl chloride battery cell by formation of excessive SO.sub.2 during high rate discharge. The method comprises the step of providing PCl.sub.5 in the cathode. Alternatively, the PCl.sub.5 may be provided in the electrolyte or in both the cathode and electrolyte as desired. The PCl.sub.5 may be incorporated in the cathode by introduction thereof into the porous carbon structure of a preformed carbon element. Alternatively, the PCl.sub.5 may be dry mixed with the carbon and the mixture formed into the desired cathode element.