Electrochemical evaluation of various commercial expanders for lead-acid battery application

As known, the performance of the negative plates of lead-acid batteries is strongly influenced by the presence of organic substances, usually referred to expanders. The expanders are generally added to the negative active material during manufacturing process. The effects of such additives mainly concern the performance at high rate of discharge and charge acceptance; additionally, they also exert other beneficial actions on the overall behavior of the negative plate. During discharge process ,passivation of the electrode starts due to the formation of a PbSO4 layer. While using an expander, the passivation of surface is prevented by causing effect with its organic part that leads to increasing in the current passed through the negative plate during discharge process and the cranking ability of the battery. Thus, discharge process is more effectively occurred when a good expander is used. . During charge process The effects of expanders are simply explained by adsorption of expander onto the metallic surface and decreasing the surface area. an organic expander impedes the process of PbSO4 reduction to Pb. This phenomenon brings about decreasing in charge acceptance ability. To evaluate different commercial expanders, the various electrochemical techniques may be used. As reported in the literature, the techniques based on cyclic voltammetry are of particular interested. the voltammetric curves provide reliable information about the amount of charge stored in the anodic part of the cycle, i.e., on the formation of sponge lead, while they do not give direct kinetic information about single processes, By plotting the amount of charge of the anodic peak as a function of the cycle number, a curve presenting a wide maximum. The difference between the maximum value of the amount of charge obtained in the presence of the expander and that obtained without the expander, has been related to the activity of the organic substance, while the difference between the number of cycles for which such maximum values are observed has been correlated to the stability of the expander. 209 In this study, five types of commercial expander were considered: Penox PE110 ,New Penox formula, Texex SA B and Jinkeli and then evaluated by 15-cycle potentiodynamic polarization test which was done in the range of -725 to -325 mV/SCE with scan rate of 120 mV/min. The working electrode was pure Pb. Also, the saturated calomel electrode and platinum wire served as reference and counter electrode respectively. To prepare the solution, 6 g of expander was directly added to 300 CC of 4.8 M H2SO4 solution, followed by mechanically stirring for 2 hr. The results showed that all the expanders enhance the maximum current for the passivation Pb surface, leading to capacity improvement. Among them, the best performance belongs to Jinkeli Company. On the other hand, the expanders negatively affected the PbSO4 to Pb reduction process, except for Jinkeli and New Penox formula. In addition based on the national standard tests on batteries, the battery made by Jinkeli and new Penox formula expander revealed a desirable capacity during cycling in low temperatures and a good charge acceptance. Expander type imax anodic (mA/cm2 ) (Discharge) imax catodic (mA/cm2 ) (Charge) Cycle 1st Cycle 15th Cycle 1st Cycle 15th Cycle Pb 0.20 0.19 -1.03 -1 PE110 Penox 0.81 1.05 -0.58 -0.6 Penox new formula 0.80 1.41 -0.85 -0.92 Texex-SA 1.34 1.02 -0.46 -0.55 Texex B 1.39 1.02 -0.71 -0.79 Jinkeli 1.39 1.4 -0.85 -0.93