Voltammetric Reduction of Sulfuryl Chloride in the Presence of Calcium Tetrachloroaluminate

Abstract

Recently, it has been suggested (1-6) that the safety of the thionyl chloride and sulfuryl chloride cells can be significantly improved by replacing the low melting lithium anode (mp 180.7~ with a high melting calcium anode (mp 839~ Thus, bQth the calciumthionyl chloride (1-4) 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. This paper summarizes our results in sulfuryl chloride solutions. ExperimentalAnhydrous lithium tetrachloroaluminate (7, 8) and anhydrous calcium chloride (9) were prepared by fusion under a flowing atmosphere of hydrogen chloride gas according to the procedures previously described. The fused salts were then treated with chlorine gas in order to oxidize any organic matter. The excess of any hydrogen chloride and chlorine gases were then removed by purging with pure dry argon gas. The anhydrous salts so prepared were solidified and stored under an argon atmosphere. Aluminum chloride (iron and water free; Fluka AG) was used as received. Sulfuryl chloride (Matheson, Coleman, and Bell Company) was refluxed over lithium metal and distilled as colorless liquid. 0.4 molar Ca(A1C14)~-SO2C12 and 1.0 molar LiA1C14-SO2C12 solutions were prepared by dissolving requisite amounts of anhydrous salts in freshly distilled sulfuryl chloride. The LiA1C14-SO2C12 and Ca(A1C14)2-SO2C12 solutions were then equilibrated with a small crystal of lithium chloride and calcium chloride, respectively, in order to neutralize traces of excess aluminum chloride, if any, in the solutions. The choice of the concentration of Ca (A1CI4)2-SO2C12 solutions used in the present study was dictated by the solubility limit (,~0.5 mol/liter) of calcium tetrachloroaluminate in sulfuryl chloride (6).A three-electrode system was used for all measurements. The reference (1 X 5 cm) and counter (3.5 X 6 cm) electrodes were both made by pressing lithium or calcium onto a nickel screen. Both electrodes were mechanically abraded and thoroughly washed with carbon tetrachloride before use. The lithium electrodes * Electrochemical Society Active Member.

Electrochemical Studies of Tetrabutylammonium Electrolytes at Carbon Cathodes in Sulfuryl Chloride Cells

“…4 for neutral, acidic, and basic (Bu)4NAIC14-SO2CI~ electrolytes. In contrast to cathodic scans in LiA1CI4-SO~CI~ and Ca(A1C14).~-SO~CI~ electrolytes (4,5,11,12), which show a reduction peak, cathodic sweeps in (Bu)4NAICI4-SO2CI~ began at less positive potentials relative to lithium, and cathodic reduction currents simply increased monotonically with no apparent limiting current.…”

“…The sulfuryl chloride battery has the potential of being used in military and commercial applications based on its high energy and power densities and useful temperature range. The most commonly used electrolyte salts for lithium and calcium sulfuryl chloride primary cells have been LiA1C14 or Ca(A1C14)~ (1)(2)(3)(4)(5)(6). However, when these electrolyte salts are used, cathode performance is necessarily limited.…”

“…Chloride ions formed at the cathode during solvent reduction accumulate in carbon cathode pores and react with lithium or calcium cations in the electrolyte to form insoluble, electronically insulating LiC1 or CaCI> These products clog cathode pores and lead to large diffusion impedances which limit cell life and cathode current density. These limitations are particularly marked in calcium cells because of relatively poor morphology of deposited calcium chloride vs. the lithium chloride product phase (2)(3)(4).…”