Processes taking place in the paste of lead-acid battery plates during soaking prior to formation and their influence on battery performance

The soaking procedure is a step in the technological process of production of lead-acid battery plates. Cured plates are left to stay in the formation solution on open circuit (i.e. soaked) for 1-4 h and after that the formation process starts. During soaking, the cured paste undergoes partial sulfation. The changes in chemical and phase composition as well as the structure of the paste and the crystal morphology of plates prepared with 3BS pastes and soaked in 1.06 or 1.25 s.g. H2SO4 solution are investigated in the present work. It has been established that during soaking the lead oxides and basic lead sulfates in the paste are hydrated first and then sulfated forming 1BS and PbSO4. The content of these phases decreases in the inner parts of the plates. This results in the formation of a heterogeneous structure and composition of the paste. The sulfation of the corrosion layer has also been investigated. Batteries with plates prepared with 3BS paste and PbSnCa grids have considerably longer cycle life, if soaked and formed in 1.06 s.g. H2SO4 solution as compared to those soaked and formed in 1.25 s.g. H2SO4 solution.