EFFECT OF CORROSION LAYER ON PHENOMENA THAT CAUSE PREMATURE CAPACITY LOSS IN LEAD-ACID-BATTERIES

An analysis is given of the results presented in a number of studies o f the phenomena that cause premature capacity loss (PCL). The work is reviewed in relation to the gel-crystal concept of the structure of th e corrosion layer (CL) and the active mass. Using a specially designed plate with lead and lead-antimony sub-grids, it has been found that t he phenomena leading to PCL proceed in the CL and at its interface wit h the positive active mass (PAM). The gel-crystal structure of this in terface is discussed. The effects of PAM density, tin and antimony con tent in the grid alloy, and PbSO4 content in the corrosion layer, on p late capacity have been investigated using specially designed tubular powder electrodes. It is established that a CL with appropriate proper ties can be formed during the curing procedure if the process is condu cted at high temperatures. The outer, porous, corrosion sublayer and i ts interface with the PAM both consist of crystal and gel zones. The e lectric conductivity of gel zones is lower than that of crystal zones and depends on the concentration of polymer chains in the gel, and on the contact between them. On cycling, the concentration of polymer cha ins is decreased. This gives rise to decrease in the electric conducti vity of the CL/PAM interface (the most critical element in the plate) and, consequently, to decline in plane capacity. Antimony and tin ions interconnect the polymer chains into an integral network that maintai ns a high concentration of polymer chains and, hence, a high electric conductivity of the CL/PAM interface. In this way, the phenomena that promote PCL are suppressed. The same effect is also achieved by increa sing the density of the PAM and/or restricting mechanically the pulsat ions of the positive-plate volume during charge/discharge cycling.