A review of state-of-charge indication of batteries by means of a.c. impedance measurements

A non-destructive estimation of the state-of-charge (SoC) of batteries faci litates optimum utilization of the battery for a given application, as well as evaluation of its state-of-health. Among various methods, a.c. impedanc e spectroscopy over a wide range of frequencies provides a variety of param eters which are functions of the SoC of a given battery. These parameters a nd their variation with SoC depend on the type of battery and on the experi mental conditions. The impedance data of sealed commercial cells are rather tedious to analyze since the results are generally the combined parameters of both the positive and the negative electrodes. Separation of the parame ters which correspond to the individual electrodes involves assumptions, th e validity of which is open to question. Nevertheless, systematic linear an d reproducible variations of measurable or computable impedance parameters with battery condition are useful indicators of the SoC in a non-destructiv e way. The present review consolidates the literature on the prediction of the SoC of batteries by means of a.c. impedance measurements. (C) 2000 Else vier Science S.A. All rights reserved.