Semiempirical Analysis of Time-Dependent Elementary Polarizations in Electrochemical Cells

Abstract

A systematic semiempirical way to analyze the variation in dc polarization with the operating time of electrochemical energy conversion devices is suggested. This includes the differentiation of the constituents of the total cell impedance, followed by the estimation of the time-dependent elementary contributions to the total polarization with the help of the theoretical analysis of an equivalent circuit. This unique method enables us to design high power energy conversion devices and, at the same time, effectively diagnose the power degradation of a cell. A comparative analysis of a fresh cell with an aged cell and the effect of temperature on polarization are exemplified. In particular, time-dependent contributions of elementary polarizations have been quantitatively suggested in each case with a strategy for the design of the materials. From this approach, power degradation after repeated battery cycling was ascribed to a rise in polarization due to the interfacial charge-transfer resistance of the cathode. Furthermore, the charge-transfer resistance of the cathode proved to be the most important factor in high rate battery discharging at ambient and low operating temperatures.