Characteristics of positive grid corrosion and deformation:
(1).The electrolyte is cloudy and the plates are rotten.
(2).Due to the corrosion of the grid, the active material of the positive plate loses its due strength and coagulation, resulting in shedding. This shedding is often in the form of lumps.
(3).Due to the corrosion of the positive grid, the active material falls off, which not only destroys the pore structure of the active material, but also gradually reduces the amount of the active material. This will inevitably lead to a decrease in the capacity of the battery and a shortened cycle life.
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Corrosion mechanism of positive grid:
(1).Oxygen deposition on the surface of lead dioxide corrosion: When the anode is charged, the positive electrode releases oxygen, which enters the lattice of lead dioxide in the form of “super stoichiometric atoms” and diffuses to the metal surface through the oxide layer. Metal oxidation. Oxidation of metal is the basic process that determines the corrosion rate of the positive electrode of lead. The temperature rises and the polarization increases, causing the oxygen diffusion rate to increase and the corrosion rate to accelerate.
(2).Catalytic corrosion: Lead dioxide is a catalyst in the reaction of oxygen evolution at the positive electrode. When oxygen is precipitated, it appears in the form of intermediate product free radicals. For example: .OH, ˙O˙, .H2SO4, etc. These intermediate products are compounded on the surface of lead dioxide, causing the lead dioxide film to loosen, thereby dissolving the metal under the film and causing corrosion.
(3).Lead–lead dioxide solid-phase reaction corrosion: There is a contact potential difference between the lead in the grid alloy and the active material lead dioxide. This potential difference is the reason for the migration of electrons from lead to lead dioxide, so corrosion occurs.
(4).There are two kinds of crystals in lead dioxide, namely α-Pb02 and β-Pb02, the layer that is in direct contact with the grid is mostly α-Pb02 and the outer layer is mostly β-Pb02, while the basic product of anodic corrosion is α-Pb02 .
(5).The corrosion of the positive plate during anodic polarization is basically carried out along the grain boundaries. Since there is an outer layer of another solid solution on the outer layer of each small grain of the alloy, an interlayer with a different composition from the grain itself is formed between the grains—the intergranular interlayer, and alloy corrosion occurs in the interlayer.