(1) Introduction to the structure of the soft pack battery cell module
The soft pack battery module is generally composed of battery core, aluminum row, copper row, inner bracket, outer frame, aluminum plate, thermal pad, sampling harness and other main components. Figure 9-13 is a more typical structure of a soft pack battery cell module. The following describes the common process flow of the module shown in Figure 9-14.
(2) Introduction to the process flow of the soft pack battery cell module
Compared with cylindrical and square battery cell modules, the following aspects need to be considered in order to make a soft pack battery cell module.
Compared with cylindrical and square batteries, soft-pack batteries are prone to liquid leakage. If liquid leakage occurs, the entire module will be scrapped, and it may even cause short-circuit burning. Why are soft-packed batteries prone to leakage? This is mainly determined by the packaging process of the cell. From the schematic diagram of the aluminum-plastic film structure (Figure 9-15), it can be seen that the aluminum-plastic film is very thin, generally not exceeding 2004um, and the innermost hot melt adhesive layer is even thinner Up. The leakage of soft-packed cells in the module: one is caused by poor cell packaging; the other is caused by unreasonably reserved cell expansion space during module design.
①The leakage problem caused by the battery cell during the manufacturing process.
From the schematic diagram of the packaging area of the soft-packed cell (Figure 9-16), the soft-packed cell has a top sealing area and a secondary top sealing area (referred to as the second sealing area). Generally, these two areas are the hardest hit areas with poor packaging. Most of the leakage will also be concentrated in these two areas.
a. From the principle of cell packaging, the difficulty of top sealing is that the tabs are drawn from the side of the package, and there are sealing tapes on the tabs that need to be fused. The tabs require more heat than other areas, so that they can be effectively fused. The sealant on the lug part, and the lug also conducts heat to other places, which may result in insufficient packaging capabilities and lead to poor packaging. Over-encapsulation may cause the hot melt adhesive layer to separate from the aluminum layer, reducing the strength of the package. In actual production, factors such as equipment abnormalities, head loss, and packaging overflow can also lead to poor top seals, resulting in cell leakage.
b. Reasons for poor packaging caused by secondary packaging: During packaging, vacuum is first performed to suck out the electrolyte that is not absorbed by the excess cells, but the electrolyte at the corners of the cells is not easy to be sucked clean. If there is electrolyte in the zone, it will generally cause poor packaging. If the drawn out electrolyte contaminates and corrodes the seal head, and it is not treated in time, it will also cause poor packaging.
② Liquid leakage caused by unreasonable module design.
If the module structure design is unreasonable, the cell will expand during use, and the cell expansion needs space. If the cell does not have enough reserved space during expansion, the cell will be squeezed. When the pressure is greater than the weak part of the package, the battery cell will burst and seal and cause the battery cell to leak. When designing a module, the module personnel generally need to communicate with the cell designer to clarify the reserved space of the cell to avoid the cell squeezing and leakage due to insufficient space.
There are currently two main welding methods for soft-pack battery modules: one is tab top sealing welding; the other is tab top welding. This method is more complicated and requires fixture bending. These two methods have their own advantages, the key is how to design to meet the needs of the product.
- Heat dissipation.
Because of the outer packaging material, heat dissipation of soft-pack batteries is a problem. Temperature has a great influence on the battery life. At present, it is generally used to add a thin aluminum plate between the batteries, and the heat of the battery core is conducted through the thin aluminum plate, and then the heat of the thin aluminum plate is conducted away by other means, so as to maintain the temperature of the battery core. The uniformity of the battery prolongs the life of the battery. Through the above analysis, the cylindrical battery cell, the square battery cell and the soft-pack battery cell module have their own advantages and disadvantages. Table 9-3 compares them briefly.