Calcium thionyl chloride cells: anode studies at low temperatures

Calcium/Ca(AlCl4)2—oxyhalide/carbon cells have been studied because of their high energy density and purported safety advantages over lithium oxyhalide cells. However, calcium anode corrosion and poor cell performance at low temperatures have impeded development of this system. At −30 °C, severe anode polarization is responsible for cell failure. Performance of pure calcium and calcium alloys in Ca(AlCl4)2—thionyl chloride electrolyte was explored. It was found that best cell performance was achieved when the components included a pure calcium anode, 1 M Ca(AlCl4)2SOCl2 electrolyte containing 7% sulfur dioxide, and a carbon cathode composed of a blend of high and low surface area carbons. At −30 °C, anode polarization is due largely to increased electrolyte viscosity and related effects. Addition of SO2 alleviates these effects to some extent. Raising the discharge temperature to −20 °C significantly improves cell performance.