Phenomena That Limit the Capacity of the Positive Lead Acid Battery Plates

Abstract

This paper is the second part of an investigation whose purpose isto establish the mechanism of the processes that proceed during dischargeand cycling of the lead dioxide plate of the lead acid battery (LAB).On the basis of this mechanism some electrical parameters that canshow the state-of-charge (SOC) and state-of-health (SOH) have tobe distinguished. In the first part of this study the shape of thecharge potential transient was examined. In this part the electrochemicalimpedance spectra of a model lead dioxide electrode was investigatedin charged and discharged states as well as the changes in impedancespectra during cycling of the electrode with high and low chargecurrents. It was established that during cycling the values of charge-transferresistance (Rct), ion diffusion resistance (Rdiff) in the reactionlayer, resistance of the grid/PAM interface (Ri), and ohmic resistanceof the electrode (R) change smoothly at first with cycling and aftera critical number of cycles have been reached, they start to increasefast. This shows that the electrode is close to the end of its life.The above parameters can be used for the determination of SOH ofthe positive LAB plate. The discharge processes take place on activecenters (ACs) in positive active material (PAM) and interface. Amodel of the structure of ACs as well as a scheme of the elementaryreactions proceeding at discharge in the ACs is proposed. Duringcycling when the number of ACs in PAM decreases and this one in theinterface increases, the capacity of the electrode decreases. Onthe basis of the changes in the impedance spectra at discharge andcharge the changes in equivalent electrical circuit are discussed.