The grid design should consider: the corrosion resistance of the grid (referring to the positive grid), the amount of paste applied to the grid, the manufacturability of the grid, the strength of the grid, the size of the grid structure, etc.
Grid design is mostly described as taking the corrosion life of the grid as the basis for the grid design. The grid material is mainly lead (Pb), and the final product of corrosion is lead dioxide (PbO2). Its chemical reaction formula is
Pb→P b4++4e (1-1)
1 mol of lead (207.19 g) requires 4F = 107.21 A·h for the entire reaction, and the electrochemical equivalent of the corrosion reaction (1-1) is
or 517.4A·h/kg (1-2)
It can be seen from formula (1-2) that if the electric energy acts on the grid for corrosion, the grid will be corroded soon. Why does the grid last so long? This is mainly due to a dense oxide layer on the surface of the grid in contact with the active material, as shown in Figure 1. It is generally believed that the composition is PbOx (x is 1 ~ 2), (between PbO and PbO2), and the reaction at the interface is a solid-state reaction and proceeds at a very slow rate. This protective layer prevents further corrosion of the grid. At the interface between the grid and the active material, since the volume of PbOx is much larger than that of Pb, with the continuous increase of PbO and reaching a certain thickness, the volume expansion will form cracks. Below the crack, corrosion begins. Corrosion proceeds at a relatively constant rate, all the time slowly.
The reason for the end of battery life is due to the corrosion of the grid, the thicker the ribs of the grid, the longer the life. The design according to the corrosion life of the ribs is theoretically reasonable, but the operability is relatively poor, there is no more accurate corrosion model for calculation, and it is far from the actual situation. Grid corrosion is carried out under the cover of active material and corrosion layer, and the environment is quite complicated. It is far from the corrosion of the same grid alloy under static conditions and in a stable acid solution, and there is no comparability. In the actual use of the battery, a very complex electrochemical system is formed due to the effects of various factors such as charging conditions, self-discharge conditions, ambient temperature, poor and rich liquid conditions, and the influence of impurities. This system together determines the corrosion of the grid, not just the corrosion of a single factor. The manufacturing method of the grid also affects its corrosion, and the calendered grid (such as drawn mesh) is much more resistant to corrosion than the gravity cast grid. The pores and slag inclusions of the gravity casting grid will affect the corrosion resistance of the grid; factors such as the process conditions during the casting of the grid will cause differences in the crystal structure of the crystallization in the grid. The alloy composition is not balanced, the corrosion resistance is different, the Ca content increases, the corrosion resistance decreases, etc. Therefore, it is difficult to calculate the grid design with corrosion resistance design. But no matter what method is used for design, grid corrosion is one of the important factors to be considered.
The grid is the carrier of the active substance, and it can also be said to be the container for the active substance. The active material determines the size of the battery capacity. After the size of the plate is determined, the width, height and thickness of the grid are determined.
Vactive = Vplate-Vgrid (1-3)
in the formula
Vactive – the volume of the active substance;
Vplate – the volume of the plate;
Vgrid – The volume of the grid.
It can be seen from formula (1-3) that reducing the volume of the grid can increase the volume of the active material. The only way to reduce the grid is to reduce the volume of the ribs, structurally, to reduce the number of horizontal bars, vertical bars (or diagonal bars), or to reduce the cross-sectional area of the ribs. Conversely, as the size of the grid increases, the active material decreases.
The craftsmanship of grid production is very important to production, not only to manufacture qualified grids, but also to consider production efficiency, energy saving and consumption reduction. The general gravity casting machine is divided into industrial plate casting machine and ordinary plate casting machine according to the size of the mold. The effective size of the mold of the ordinary plate casting machine is 320mm × 180mm. For the small grid, it is necessary to design a large craft grid composed of multiple small pieces, and design the craft hanging ears. After the raw or cooked electrode plates are prepared, they are divided into small electrode plates. When the process grid is cast, it is necessary to ensure that the size, structure and weight of each small piece are the same, and the quality meets the requirements of the inspection specification. In the production process after the grid, the design structure of the process grid, the position of the process mounting ears, etc. have an important impact on the convenience and operability of production.
The grid has a certain strength is necessary in production. The grid strength of lead-antimony alloy composition is relatively high, and there is basically no strength problem in production. For lead-calcium alloy grids, low strength is a factor that affects production, as well as quality. Calcium increases strength in lead-calcium grids, but when calcium is added in a large amount, the performance of the battery will decrease rapidly. So calcium cannot exceed the amount given by the process. When casting the plate, when the cast grid is demolded and falls to the connecting plate of the machine, sometimes it will be deformed, so the speed of casting the plate should not be too fast. When the uncut grid enters the cutting edge, the sliding and contact with the positioning plate below will also deform the grid. When the temperature is high in summer, the grid cooling is slower and deformation is more likely to occur. After age hardening of the grid, the strength of the grid does not change when the plate is coated.
enough, the painted green board is also easy to deform, resulting in waste. Therefore, under the alloy conditions required by the process, the purpose of increasing the strength should be achieved through a reasonable grid arrangement structure, process hanging ears, and auxiliary parts.
The basic requirements of the battery are the initial capacity, life, weight, specific energy, and type of use of the battery. The structure of the grid can be roughly determined according to these factors (the width and height and the position of the tabs are determined by the battery tank body), and the general situation of the grid can be further calculated.
It is more practical to use empirical design after the grid design is determined in a large direction. That is, according to the specific requirements of the battery type, grid alloy battery, grid thickness and structure, the design structure is estimated, and the grid design is carried out, and manufacture the battery according to the process. The battery has undergone laboratory life test and practical life test, and the state of the grid is dissected to provide a basis for the battery grid of the same type and the same conditions.
The alloy of the grid remains unchanged, the production method remains unchanged, and the battery has similar uses. On the basis of the above experience, a new grid can be properly adjusted and designed, and then accumulated through experiments. This accumulation has formed unique design ideas and methods, which are also practical and effective methods.
The grid produced under this design idea has a stable alloy, and the effect achieved is in line with expectations. The alloys of some manufacturers are unstable, and one batch is one sample. This situation will have a serious impact on the consistency of the battery.