What is a battery grid?

 What is a battery grid?

The component that supports the active material in the lead-acid battery plate is usually a grid-like structure, called a grid. The grid has three functions in the battery, one is that the grid supports the active material and is the carrier of the active material; the other is that the grid is the conductor of the active material, and the electricity stored by the active material flows out and inflow through the grid. The main function of the body is to use lead-based alloys as the grid material. In addition, there are also studies using non-conductor materials or non-lead-based materials to make plates by plating lead on the surface.

Grids, such as lead-plated plastic grids, lead-plated copper grids, etc., are used for negative grids; third, the corrosion products of the grids should protect the grids, reduce corrosion, and reduce the interface resistance combined with active substances. In the past, the interfacial resistance between the grid and the active material was not obvious due to the use of lead-silver alloys, but with the large-scale use of lead-calcium alloys, this problem has become more prominent, and sometimes even seriously affects the performance of batteries. Therefore, reducing corrosion and reducing interface resistance should be considered as one of the functions of battery grids.

The grid is a grid-like structure, and the cast grid is composed of a frame, ribs (horizontal ribs, vertical ribs, diagonal ribs, reinforcing ribs, auxiliary ribs), pole ears, and plate corners (some do not need); The grid is composed of upper and lower borders, mesh ribs, and pole ears. The punching grid has upper and lower borders and left and right borders, and the holes are formed by punching by die. The voids in the middle of the grid are filled with active substances.

The environment in which the grid is used is very harsh. First, the plates work in 5%~41% sulfuric acid. The active material of the plate is a porous material, and part of the grid will be exposed to the acid solution, so the grid material must withstand the corrosion of sulfuric acid, and cannot be dissolved in the sulfuric acid solution, and a small amount of corrosion products will not form toxic side effects to the battery; during the charging process of the battery, the positive electrode is in an oxidized state and the negative electrode is in a reduced state, so the grid material must have the properties of resistance to oxidation and reduction. To meet this requirement, it is very difficult to select the grid material.

At present, the grid materials are mainly non-lead-based materials such as lead-based alloys or plastic lead plating. Commonly used lead-based alloys include lead brocade (Pb-Sb), lead-calcium (Pb-Ca), lead-tin (Pb-Sn) and other alloys, which are used for positive and negative grids;

Non-lead-based alloy materials include plastic lead plating, copper lead plating, etc., which are mainly used for negative grids.

Lead-based alloy grid in use, although it is a material with certain corrosion resistance and redox resistance, as the battery is used for a long time and the charge and discharge are repeated, the grid will still change, and the positive grid will gradually be oxidized to produce corrosion products. Generally, the corrosion products are mainly lead compounds and a small amount of alloy compounds, which have no or slight side effects on the battery. When the lead-based alloy positive grid is oxidized and corroded to the point that it cannot support the active material, or can not quickly export and guide the electricity, the life of the battery will be terminated. Therefore, it is said that the battery life is calculated according to the corrosion rate of the positive grid of the battery. In most cases, the negative grid is in a reduced state, and the grid will not corrode, which is the main reason why the lead-plated grid can be used for a long time.

In the production process, according to the requirements of the mold size of the casting machine, the small grids are often connected together to form a large piece, which is called a large piece of technology, which facilitates production, improves efficiency and reduces losses. After the large pieces are formed and dried, the small pieces are separated, and the frame is polished to form a plate product. In order to facilitate production, large grids should be designed with process tabs, also known as false ears. After the prosthetic ear is divided, it is returned to the casting workshop for reuse. With the development of battery formation technology, the battery formation is assembled with green plates, and the plates are directly separated after the green plates come out, and the structure of the large grids in the process does not need to have the auxiliary function of plate formation. The structure of the grid is shown in Figure 1.

What is a battery grid?
Figure 1 – Structure of the grid
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