EIS study of electrochemical battery discharge on constant load

The impedance of electrochemical battery has been measured using a classical impedance-measurement apparatus to control the battery discharging into a constant load under current perturbation. This new method can be used even when the discharge current is greater than the maximum current that could be supplied by the regulation of the impedance-measurement apparatus used. Impedance measurements were first carried out on sealed Ni-Cd cells with a capacity of 0.65 Ah using the classical modulated current method and the new proposed method. The results show that the impedance diagrams, obtained during battery discharge through a constant load R, are identical to those obtained during discharges at a constant current with value Umean/R where Umean is the mean voltage of the battery during its natural discharge. These comparative measurements validate the proposed impedance-measurement method which can be used to test all types of batteries or fuel cells. Impedance measurements are presented for sealed lead/acid cells with a capacity of 25 Ah and battery discharge currents greater than the maximum current that the regulation system could supply. These measurements show that the proposed method may be used with classical impedance-measurement set to test high-capacity and low-impedance batteries during discharge into a constant load.