Dynamic characterization of small lead-acid cells

Three sizes of small valve regulated (VRLA) commercially available lead-acid cells were investigated and characterized for their dynamic properties by ac impedance spectroscopy and other electrochemical techniques. All cells were of the limited electrolyte type and no additional electrolyte was introduced during the studies. The data indicates a very significant increase in cell impedance at lower states of charge, as expected. In charging studies close to the fully charged state, some unexpected impedance data were observed. Complex impedance plots indicate a passive film formation, probably associated with the recombination surface film. The investigations included cells in various states of charge as well as cycling history including positional orientation studies. Equivalent circuits were derived from ac impedance spectroscopy and the parameters studied as a function of the cell's state-of-charge. Furthermore, the voltage response of the cells was theoretically generated from the ac impedance spectroscopy using Fourier transform analysis and found to be similar to the measured cell responses.