A Study of the Calcium‐Thionyl Chloride Electrochemical System

Abstract

The use of calcium metal as an anode in SOC12 electrolytes was investigated. Calcium showed an open-circuit potential (OCP) of 3.22V vs. a carbon cathode in IM Ca(AICI4)2-SOCI2 electrolyte. Hermetically sealed D cells, when discharged at 1 rnA/cm 2, displayed level discharge plateaus of 2.8V. SEM photographs indicated the rapid formation of a crystalline layer on the anode; the composition of this film was established as CaCI2. Storage of calcium samples in Ca(AICI4)2-SOCI2 electrolyte resulted in corrosion of the metal. This corrosion was particularly pronounced at 55~ and it appeared to be a fundamental behavior which was not eliminated by rigid control of electrolyte purity. The following cell chemistry was suggested by chemical analysis of discharged electrolytes and cathodes 2Ca + 2SOC12-> SO9. + 2CaC12 + S Electrodeposition experiments indicated no evidence for the plating of Ca onto a nickel substrate. One of the principal incentives for investigating the Ca/SOC12 system is that calcium anodes have the prospect for higher temperature operation when compared with lithium anodes. The higher melting point of calcium (839~ compared to lithium (180~ would obviate the possibility of anode melting under high temperature stress, e.g., as a result of large short-circuit currents generated in a high power cell configuration. A comparison of the calculated theoretical energy densities of lithium and calcium/SOC12 cells is presented below assuming reaction products of SO2, S, and either LiC1 or CaC12. These values indicate that Cell potential Energy density Specific energy