Title

Anode passivation in calcium thionyl chloride batteries

Date of Completion

January 1989

Keywords

Engineering, Chemical|Engineering, Metallurgy|Engineering, Materials Science

Degree

Ph.D.

Abstract

Properties of the solid electrolyte interface of the calcium thionyl chloride battery have been studied with impedance spectroscopy and DC polarization. Anodes of pure Ca metal, a Ca-10% Sb alloy, and a Ca-2% Li alloy were used. Impedance spectroscopy results were modeled with an equivalent circuit model which permitted determination of parameters describing the solid electrolyte interface (resistance and capacitance values), the double layer capacitance, the charge transfer resistance, and the solution resistance. The polarization measurements permitted determination of anodic and cathodic Tafel slopes which, with the impedance data, allow calculation of the corrosion rate of the anode in the thionyl chloride electrolyte.^ Shelf life calculations, obtained from the corrosion rate measurements, permit comparison of the performance of the three anodes investigated. Based on a 0.020 inch specimen, the shelf life of the pure Ca was 3 years; that of the Ca-2% Li, 5.5 years; and that of the Ca-10% Sb, 2.9 years.^ The open circuit voltage was also monitored over the exposure period and related to the polarization resistance in semi-log polarization (V versus log i) plots. The behavior evidenced in these diagrams suggest that the solid electrolyte interface is a n-type lattice with Cl$\sp-$ vacancies and, in the alloy anodes, monovalent Li$\sp+$ cations and trivalent Sb$\sp{+3}$ cations on the Ca$\sp{++}$ sublattice. ^