Processes in positive lead/acid battery plates during soaking prior to formation

Abstract

Before switching on the current for formation of the active mass of lead/acid batteries, cured plates stay for a certain period of time in H 2SO 4 solution at open circuit. This period is called ‘soaking’ or ‘pickling’. The cured paste consists of PbO (α+β) and basic lead sulfate (3BS or 4BS). they are unstable in H 2SO 4 solution and, hence, the chemical reactions of sulfation proceed. This work reports a study of these chemical processes for 3BS pastes through chemical and X-ray phase analysis and scanning electron microscopic observations. Sulfation has been studied during soaking in H 2SO 4 solutions of three concentrations (sp. gr. 1.05, 1.15 and 1.25) for 8 h. Soaking was performed in batteries assembled with cured plates. It is established that soaking in H 2SO 4 of sp. gr. 1.05 results in the formation of 3Bs, 1BS and, after 4 h, small amounts of PbSO 4. In more concentrated H 2SO 4 solutions (sp. gr. 1.15 and 1.25), PbSO 4 predominates. Capacity, cold-cranking and cycle-life tests have been performed with batteries soaked in the three H 2SO 4 concentrations for different periods of time. It is established that, depending on the acid concentration and the duration of soaking, the battery capacity may be incrased by 10%, and the time of high-rate discharge at −18 °C may be prolonged by about 1 min. Battery life may also be improved. These results indicate that soaking should be introduced as a separate technological procedure under constant control in order to ensure good and stable battery performance characteristics.