Effect of state of charge on impedance spectrum of sealed Ni-MH cells

Alternating current impedance spectroscopy was used to determine the state of charge of sealed Ni-MH cells in wide frequency range. A modified Randles ' circuit was used to fit the impedance data. The effect of state of charge on the equivalent circuit parameters,.e.g., phase angle, phi, impedance mo dulus, \Z\, equivalent series capacitance, C-s, ohmic resistance R-Omega, a nd charge transfer resistance R-r was determined. It has been found that th e impedance parameters were sensitive to state of charge at low frequencies . (C) 1999 Elsevier Science S.A. All rights reserved.