Residual Capacitance Estimation in Lithium-Thionyl-Chloride Chemical Current Sources using Impedance Spectroscopy

Abstract

Purpose of this work is to elaborate operational and reliable method for ensuring non-destructive control over primary lithium-thionyl-chloride chemical current sources (LCCS) using the impedance spectroscopy. Results and conclusions presented in this work are based on a series of experimental studies. Result reliability was experimentally proven on models and samples with known characteristics. Mathematical apparatus used in processing experimental data using the Fourier transforms allows obtaining information on impedance in a wide frequency range based on results of a single experiment and prompt calculating its main parameters (impedance imaginary value at the hodograph extreme point, its frequency, high-frequency resistance and phase). Ways to reduce the passive film influence, which is appearing on the lithium electrode during storage and operation, on the impedance characteristics are shown. Based on the electrochemical impedance spectra analysis, most informative frequency ranges were determined, and correlates were found connecting the impedance characteristics with the investigated current source state. It is proposed to use the phase angle value measured at the impedance hodograph extreme point as a correlate allowing to estimate the LCCS residual capacitance. It was determined that in assessing the LCCS discharge degree in the range of 0--70 % residual capacity, results of impedance spectroscopy are being quite informative