Impedance spectroscopy as a technique for monitoring aging effects in nickel hydrogen and nickel-metal hydride batteries

Impedance spectroscopy is evaluated as a method for the early detection of aging effects in electrochemical cells. AC impedance and phase measurements were made on about 85 cells in various stages of life testing. Spectral data from 3 mHz to 30 kHz were acquired on fully discharged cells. Impedance spectroscopy provided an effective means of detecting age diversity present in the test population. This could be seen in the data at very low frequencies, below 1 Hz. This is the so called Warburg region where the availability of charge carriers is diffusion controlled. Both raw impedance data and Argand diagrams, in which reactance is plotted as a function of resistance, represent useful graphical outputs