All-solid-state measurements of electrical properties of passive films on lithium

An all-solid-state cell for studying the electrical properties of passive films on lithium formed in thionyl chloride was constructed in which the counterelectrode was a sheet of metallic lithium pressed against the surface of the passive film. In modeling the impedance response of the cell the poor electrical contact between the passive film and the counterelectrode was taken into account. Unlike previous studies, passive film thickness calculated from the impedance response measured was comparable to the thickness observed by scanning electron microscopy, i.e., approximately 80 mu m. In the temperature range 30 to 150 degrees C, the activation enthalpy for bulk ion conduction was 0.65 +/- 0.05 eV which is approximately 0.2 eV higher than the value measured by Haven(16) at 300 to 450 degrees C for a LiCl single crystal. The same value of activation enthalpy was found for the reference cell in which LiCl was evaporated on a platinum substrate and the counterelectrode was again a pressed lithium sheet.