Rate‐Determining Step Investigations of Oxidation Processes at the Positive Plate during Pulse Charge of Valve‐Regulated Lead‐Acid Batteries

In order to develop electric vehicles (EVs), electrochemical scientists and engineers have paid great attention to the study of batteries in recent years. Now, while new types of batteries are still in development, the valve-regulated lead-acid (VRLA) battery is a near-term candidate for EV applications in mass markets. The recharge time for valve-regulated lead-acid batteries has been reduced and is now less than 5, 15, and 240 min for 50, 80, and 100% charge. However, many other problems arise from pulse charging such as reduced cycle life of the battery, corrosion of the positive-electrode grid, loss of electrolyte, and thermal management. The kinetic processes of both PbSO{sub 4} oxidation and the oxygen evolution reactions were studied under pulse charging conditions. Three kinds of diffusion processes appeared in the positive active mass. The time intervals required to relax the respective concentration polarizations were about 0.1, 300, and more than 10,000 s. At the beginning of the pulse charge, the passivation layer formed between the grid and active mass at the positive plates exhibited a poor electronic conductivity and impeded the diffusion of O atoms. Thus, the electrode polarization increased and oxygen evolution accelerated. Following the initial pulse, the diffusion of Omore » atoms became rapid while the concentration of ions such as HSO{sub 4}{sup {minus}} and SO{sub 4}{sup 2{minus}} at the reaction surface increased gradually so that their diffusion became dominant in the solution near the reaction surface. For longer times, the charge rate was controlled by the diffusion of these ions in the micropores of the active mass. The electrode polarization, oxygen evolution, and loss of water can be inhibited by using a pulse discharge or/and prolonging the off-time of pulse charge.« less