Corrosion of positive plate in lead-acid battery

Corrosion of positive plate in lead-acid battery

What is the corrosion of the positive plate in the lead-acid battery?

It can be seen from the charge-discharge reaction process of lead-acid batteries, when the positive plate is in the charging reaction, Pb and O have a process of combining and separating.

When discharging, O is first separated from the bound state, and then combined with H+ to generate H2O; when charging, O in the water obtains energy from the external circuit, separates from H+, recombines with Pb, and generates PbO2, which is an oxidation process. This kind of reaction does not exist on the negative electrode, and there is only the separation and reunion of Pb and SO42- on the negative electrode.

It can be seen that during the charging process, the Pb on the positive electrode is re-oxidized. In the actual battery structure, the charging current enters the active material through the grid in the middle of the active material on the electrode plate, and the grid is also in contact with the electrolyte. In the charged state, when Pb is oxidized, the positive grid is inevitably locally oxidized. Every time it is charged, the grid is oxidized once. If the active material has been reacted in quantity, the oxidation reaction generated by the charging current at this time is all used to decompose water and oxidize and corrode the positive grid.

It can be known from the electrochemical reaction principle that even under the condition of not charging, the positive plate in the lead-acid battery is constantly being corroded, but the rate is low. During charging, corrosion accelerates. During overcharging, the positive grid is oxidized and the inside of the grid is corroded through the alloy crystal lattice, and at the same time it deforms, causing the grid to increase linearly in size, or even break, which is an important cause of battery damage. In addition, when there are corrosive impurities (such as organic acids, etc.) in the electrolyte, the corrosion of the positive grid is significantly accelerated. Decomposing the discarded battery, it can be seen that the positive grids are corroded to different degrees. Since oxidative corrosion caused by overcharge does not exist on the negative electrode, there is often no obvious corrosion on the negative electrode grid.

Obviously, taking protective measures for the positive grid and adding some corrosion inhibitors to reduce overcharge is a measure to improve the battery life.