III.1. Structure of positive (PbO2) active mass

The structure of PAM obtained during formation of the plates consists of two structural levels and is presented on Fig. 1.

Microstructural level. The smallest building element of PAM structure is the PbO2 particle. A certain number of PbO2 particles interconnect into agglomerates. At this microstructural level the electrochemical reaction of discharge proceeds. This level determines the active surface area of PAM.

Macrostructural level. A huge number of agglomerates, and in some cases individual particles, interconnect to form aggregates (branches) or porous mass. Micropores are formed between the agglomerates building up the aggregate. Aggregates (branches) interconnect to form: (i) skeleton, which is connected to the grid through an interface or (ii) porous mass. Macropores are formed between the aggregates along which H2SO4 and H2O flows move between the plate interior and the bulk of electrolyte (main transport system of PAM). The type of formed PAM macrostructure depends on the size of crystals in the cured paste (3BS, 4BS, PbO, PbSO4). When the cured paste contains large particles (>10 μm) the macrostructure has skeleton appearance. If the cured paste contains small particles (<2 μm) a porous mass is formed.


  1. D. Pavlov, E. Bashtavelova, A model of the structure of the positive lead-acid battery active mass, J. Electrochem. Soc., 131, (1984) 1468
  2. D. Pavlov, E. Bashtavelova, Structural properties of the PbO2 active mass determining its capacity and the "breathing" of the positive plate during cycling, J. Electrochem. Soc., 133 (1986) 241
  3. D. Pavlov, E. Bashtavelova, V. Iliev, Structure of the lead-acid battery active masses, Advances in Lead-Acid Batteries, Proceedings of the International Symposium, Vol.84-14, p. 16, Electrochem. Soc. Inc., Pennington, USA, 1984

PhD Theses

E. Bashtavelova, Structure of the lead dioxide active mass and its influence on the operation parameters of the positive lead acid battery plates.

Keywords: structure of PAM, PAM microstructure, PbO2 particle, agglomerates of PbO2 particles, PAM macrostructure, agglomerates interconnected in aggregates in PAM, PAM skeleton, PAM porous mass, macropores of PAM