The first reason: caused by the battery itself
Why do you say that? In the previous issue, we learned the working principle of lead-acid batteries. The process of charging and discharging lead-acid batteries is the process of electrochemical reaction. When charging, lead sulfate forms lead oxide, and lead oxide is reduced to lead sulfate during discharge. Lead sulphate is a substance that is very easy to crystallize. When the concentration of lead sulphate in the electrolytic solution in the battery is too high or the static idle time is too long, it will "carry" into a group and form small crystals. These small crystals will attract the surrounding area. The lead sulfate, like a snowball, forms a large inert crystal. When the lead sulfate is crystallized, it can not be reduced to lead oxide, but also precipitates on the electrode plate, causing the working area of the electrode plate to decrease. This phenomenon is called vulcanization. At this time, the battery capacity will gradually decrease until it is unusable. When the lead sulfate is piled up in a large amount, lead particles are attracted to form lead branches, and the lead bridge between the positive and negative plates causes a short circuit of the battery. If there is a gap in the surface of the plate or the sealed molded case, the lead sulfate crystals will accumulate in these gaps and cause expansion tension, which eventually causes the plate to break off or the outer casing to rupture, resulting in irreparable physical damage of the battery. Therefore, the main mechanism leading to failure and damage of lead-acid batteries is that the battery itself cannot avoid vulcanization.
The second reason: the reason for battery production
Various battery manufacturers have adopted various methods for the particularity of lead-acid batteries for electric bicycles. The most typical method is as follows:
1 Increase the number of plates. The original design of the single-frame 5-piece 6-piece system was changed to 6-piece 7-piece system, 7-piece 8-piece system, and even 8-piece 9-piece system. Increase the battery capacity by reducing the thickness of the plates and the spacers and increasing the number of plates.
2 increase the specific gravity of the battery sulfuric acid. The original sulfuric acid specific gravity of the floating battery is generally between 1.21 and 1.28, and the sulfuric acid specific gravity of the battery of the electric bicycle is generally around 1.36 to 1.38, which can provide a larger current and increase the initial capacity of the battery.
3 increase the amount and proportion of lead oxide active material active material. Increasing lead oxide increases the electrochemical reaction species involved in the discharge, which increases the discharge time and increases the battery capacity. Through these measures, the initial capacity of the battery satisfies the capacity requirements of the electric bicycle, and in particular, the characteristics of the large current discharge of the battery are improved. However, as the number of plates increases, the capacity of sulfuric acid decreases, and the battery heat causes a large amount of water loss. At the same time, the probability of micro-short circuit and lead-bridge bridging of the battery increases. Increasing the specific gravity of the sulfuric acid increases the initial capacity of the battery, but the vulcanization phenomenon is more serious. One of the most basic principles of sealed batteries is that after the oxygen is separated from the positive electrode plate, the oxygen is directly sent to the negative electrode plate and absorbed by the negative electrode plate to be reduced to water. The parameter of the technical index of the battery is called “sealing reaction efficiency”. This phenomenon is called “oxygen”. cycle". In this way, the battery has little water loss, achieving "maintenance-free", that is, no water is added. For this reason, it is required that the capacity of the negative electrode plate is made larger than that of the positive electrode plate, which is also called a negative electrode transition. Increasing the active material of the positive electrode plate inevitably reduces the transition of the negative electrode, the oxygen cycle becomes worse, the water loss increases, and the vulcanization is caused. Although these measures increase the initial capacity of the battery, they cause water loss and vulcanization, and water loss and vulcanization will contribute to each other, and the end result is to sacrifice the life of the battery.
4 There is also the problem of the virtual group loading of the welding. The place where the solder joint is easy to occur is the plate. Each cell has 15 plates, which are 15 solder joints. One battery has 6 cells, and there are 90 solder joints. One battery consists of 3 12V batteries, and there are 270 solder joints. . If there is a virtual solder joint in the solder joint, the capacity of the single cell decreases, and the cell forms a backward battery, causing the entire battery to lag behind, and the battery will form a serious