A Study of the Calcium‐Thionyl Chloride Electrochemical System

Abstract

The use of calcium metal as an anode in SOCl2 electrolytes was investigated. Calcium showed an open‐circuit potential (OCP) of 3.22V vs. a carbon cathode in 1MnormalCafalse(AlCl4)2‐SOCl2 electrolyte. Hermetically sealed D cells, when discharged at 1 mA/cm2, 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 CaCl2 . Storage of calcium samples in normalCafalse(AlCl4)2‐SOCl2 electrolyte resulted in corrosion of the metal. This corrosion was particularly pronounced at 55°C 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 cathodes2normalCa+2SOCl2→SO2+2CaCl2+SElectrodeposition experiments indicated no evidence for the plating of Ca onto a nickel substrate.

Voltammetric Reduction of Sulfuryl Chloride in the Presence of Calcium Tetrachloroaluminate

“…1) may be, analogous to LiA1C14-SO2Clz solutions, attributed to the reduction of chlorine and sulfuryl chloride, respectively C12 + Ca + + + 2e --> CaC12 [1] SO2C12 + Ca + + + 2e --> CaClz + SO~ [2] Since, calcium chloride was found to be insoluble in sulfuryl chloride solutions, the deposition of calcium chloride at the glassy carbon electrode surface results in its passivation. The total charge required to passivate the electrode surface was measured by integrating the area under the cathodic reduction peaks at each scan rate and is plotted in Fig.…”

“…Thus, bQth the calciumthionyl chloride (1)(2)(3)(4) and calcium-sulfuryl chloride (5,6) cells have been investigated during the past three years. For both these cells, solutions of lithium tetrachloroaluminate or calcium tetrachloroaluminate have been used as electrolytes.…”

“…However, the cathode capacities in calcium cells using lithium tetrachloroaluminate solutions as electrolytes were found (5,6) to be smaller than the cathode capacities in corresponding lithium cells. The cathode capacities in calcium cells were even smaller if solutions of calcium tetrachloroaluminate were used as electrolytes (2,5,6). Therefore, in order to gain an insight into the cathodic process in calcium cells, we have studied the voltammetric reduction of sulfur oxychloride solvents at smooth glassy carbon electrodes in solutions containing calcium tetrachloroaluminate.…”

Cathode Performance Improvement in Calcium‐Thionyl Chloride Cells

“…Lithium ions were assumed to be intercalated in the interchain space (2). The overall reaction of lithium intercalation was represented by the following equations (3,4) 2Li + + 2e-+ M4+X2-X~ 2 ~ (Li+)2M 4+ (X2-)3 [1] Li + + e-+ (Li+)2M 4 § (X2-)3 ~ (Li+)3M3+(X2-)3 [2] The X-X dimer is reduced in the first reaction and the transition metal in the second. Three lithiums can react with a MX3.…”

“…The calcium-thionyl chloride battery system has been attracting considerable attention (1)(2)(3)(4)(5)(6) for its high opencircuit potentials (->3.2V), high theoretical energy density (1100 Wh/kg), broad operating temperature range~ and projected high degree of system safety. This increased safety is due to the high melting point of calcium metal (839 ~ vs. 180~ for lithium) which precludes the likelihood of difficulties traceable to a molten anode.…”