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 th at positive active mass (PAM) agglomerates comprise not only crystal z ones but also hydrated gel zones. The latter are built of linear hydra ted polymer chains that interconnect the crystal zones and have both e lectron and proton conductivity. The reasons for the premature capacit y loss (PCL) of batteries has been looked for in: (i) decrease in the electroconductivity of the gel zones due to the lack or insufficient c ontent of dopants (tin, antimony, etc.) that improve the contacts betw een the polymer chains and interconnect them into an integral system w ith high electron and proton conductivity; (ii) decrease in the PAM de nsity on pulsation of the plate upon cycling, leading to a decrease in concentration of polymer chains in the gel that interconnect the aggl omerates to form the skeleton of the PAM; (iii) decrease in degree of hydration of the corrosion layer, which is important for both its flex ibility and its ability to take on the mechanical stresses that are cr eated as a result of oxidation of the grid metal. Based on the gel-cry stal concept of the PAM, technological methods have been suggested for suppressing the phenomena that cause PCL (er.g., use of 4PbO PbSO4 (4 BS) pastes, high-temperature curing, addition of dopants such as tin a nd 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 in teraction with H2SO4. Appropriate selection of grid-alloy additives (a ntimony, tin, etc.) give rise to increases in the rate of oxidation of PbO to PbOn in the corrosion layer, the value of the stoichiometric c oefficient n, and the degree of hydration of the corrosion layer. Al t hese effects will result in the suppression of the phenomena of PCL. B ased on the gel-crystal concept, some design methods have also been su ggested to alleviate PCL. Thus, solving the problems related to PCL is only possible when design and technological methods are applied in co mbination.