Processes during battery storage

During storage of partially wet-charged and dry-charged lead-acid batteries, some processes occur which lead to self-discharge and passivation of the plates. The self-discharge reactions at the two types of plates have been identified. The capacity loss during storage is reversed on battery charge. Passivation phenomena depend on the structure of the plates.

Processes in separators. In the case of partially wet-charged batteries, PbSO₄ crystals form in the separators during storage. When the battery is subjected to charge and overcharge these crystals transform into Pb and PbO₂ and cause short circuits between the plates leading to battery failure.

Processes at positive plates. Passivation of the positive plates manifests itself by an abrupt drop in discharge potential with no substantial change in discharge time. This is due to the formation of a nonstoichiometric oxide PbO_n (n<1.5) by a reaction between the grid and the PbO₂ of the corrosion layer. This oxide has high electric resistance. During battery charge it is oxidized to PbO₂ by the O atoms and O radicals formed by the high anodic polarization. They penetrate through the corrosion layer and oxidize the PbO_n layer to PbO₂. The plate is depassivated with an abrupt rise of its discharge potential.

Processes at negative plates. Passivation of the negative plates leads to shortening of the discharge time with no substantial change in discharge potential. Negative plate passivation is a result of formation of a PbO (or PbSO₄) film at the interface between the skeleton and energetic structures of the lead active mass. These films interrupt the electric contact between skeleton and energetic structure thus decreasing plate capacity. During battery charge the PbO (or PbSO₄) film is reduced to lead and the electronic contact between the two structures is restored. The negative plates depassivate and the capacity increases.

References

1. V. Iliev, D. Pavlov, Self-discharge and passivation phenomena in lead-acid batteries during storage, J. Electrochem. Soc., 129 (1982), 453
2. S. Ruevski, V. Iliev, D. Pavlov, Methods for decreasing lead acid battery mentenance. Chemie and Industry (in Bulgarian), 3 (1982) 124
3. D. Pavlov, “Power sources for Electric Vehicles”(B.D.McNicol, D.A.J. Rand eds) Chapter 5.1. Lead-Acid Batteries, pp. 386-408, Elsevier, Amsterdam, 1984

Keywords: battery storage, wet-charged lead-acid battery, dry-charged lead-acid battery, self-discharge of lead-acid battery, passivation of lead-acid battery plates