PROCESSES IN POSITIVE LEAD-ACID-BATTERY PLATES DURING SOAKING PRIOR TO FORMATION

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 H2SO4 solution at open circuit. This period is called 'soaking' or 'pickling'. The cured paste consists of PbO (alpha + beta) and basic lead sulfates (3BS or 4BS). They are unstable in H2SO4 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 H2SO4 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 H2SO4 of sp. gr. 1.05 results in the formation of 3BS, 1BS and, after 4 h, small amounts of PbSO4. In more concentrated H,SO, solutions (sp. gr. 1.15 and 1.25), PbSO4 predominates. Capacity, cold-cranking and cycle-life tests have been performed with batteries soaked in the three H2SO4 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 increased by 10%, and the time of high-rate discharge at -18 degrees 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.