SUPPRESSION OF PREMATURE CAPACITY LOSS BY METHODS BASED ON THE GEL-CRYSTAL CONCEPT OF THE PBO2 ELECTRODE

Based on experimental data, the concept has been developed recently that positive active mass (PAM) agglomerates comprise not only crystal zones but also hydrated gel zones. The latter are built of linear hydrated polymer chains that interconnect the crystal zones and have both electron and proton conductivity. The reasons for the premature capacity loss (PCL) of batteries has been looked for in: (i) decrease in the electroconductivity of the gel zones due to the lack or insufficient content of dopants (tin, antimony, etc.) that improve the contacts between the polymer chains and interconnect them into an integral system with high electron and proton conductivity; (ii) decrease in the PAM density on pulsation of the plate upon cycling, leading to a decrease in concentration of polymer chains in the gel that interconnect the agglomerates to form the skeleton of the PAM; (iii) decrease in degree of hydration of the corrosion layer, which is important for both its flexibility and its ability to take on the mechanical stresses that are created as a result of oxidation of the grid metal. Based on the gel-crystal concept of the PAM, technological methods have been suggested for suppressing the phenomena that cause PCL (er.g., use of 4PbO PbSO4 (4BS) pastes, high-temperature curing, addition of dopants such as tin and antimony to the grid alloys, etc.). The role of the corrosion layer in suppressing PCL has been disclosed and especially the significance of the stoichiometric coefficient n of PbOn (1<n<2) in the layer, as well as the factors that give rise to an increase in the value of this parameter. The stoichiometric coefficient exerts an influence on both the electroconductivity of the corrosion layer and the rate of its interaction with H2SO4. Appropriate selection of grid-alloy additives (antimony, tin, etc.) give rise to increases in the rate of oxidation of PbO to PbOn in the corrosion layer, the value of the stoichiometric coefficient n, and the degree of hydration of the corrosion layer. Al these effects will result in the suppression of the phenomena of PCL. Based on the gel-crystal concept, some design methods have also been suggested to alleviate PCL. Thus, solving the problems related to PCL is only possible when design and technological methods are applied in combination.