(1) Introduction to the structure of the square battery cell module
The square battery module is generally composed of battery core, end plate, side plate, bottom plate, aluminum sheet (usually called Busbar), wiring harness isolation plate, upper cover, end plate insulation cover and other main components. Figure 9-11 is a more typical square battery cell module structure. The following describes the common process flow of the module shown in Figure 9-12.
(2) Introduction to the technological process of the square battery cell module
Through the previous introduction to the cylindrical battery cell module, the difference between these two modules is still relatively large, and the difference in the shape of the battery cell leads to the difference in the structure and process flow of the module. The following focuses on the differences between the square battery cell module and the cylindrical battery cell module, and the analysis is mainly from the following aspects.
- The insulation of the module.
Early square cell modules generally used plastic frames to fix the cells, which is similar to the current cylindrical cell modules, and the insulation of the modules is relatively good. However, if the square cell is fixed with a plastic frame, three problems may occur: one is that the cell cannot be effectively fixed due to the poorly matched size of the cell and the plastic frame; the other is that the cell size is not well controlled and the module is not fixed. Good assembly: Third, the weak structural strength of the plastic frame may cause the plastic frame to break due to the expansion of the battery core. With the development of technology, a metal outer frame is currently used to fix the battery cell, which can effectively avoid the disadvantages of fixing the battery core with a plastic frame.
Since the metal outer frame is used to fix the battery core, if the insulation protection is not done well, the insulation will fail. Generally, insulation tests are required before and after welding. If the insulation is found to be poor during the test before soldering, it can be solved by general rework processing; if the insulation is found to be poor during the test after soldering, it is generally not easy to handle, and the module may be scrapped in serious cases. When insulation is done, insulation pads or insulation plates are generally added to the inner side of the end plates and side plates. Insulation treatment is also required between the cells, which is usually isolated by applying glue or spraying glue.
- Module size control.
If the critical dimension deviation of the module is too large, the module cannot be installed, and the module will be scrapped directly. To control the critical size of the module, you need to consider the following three aspects
①Battery size matching: when matching the battery, the thickness of the battery should be strictly checked, and the problem of poor size of the incoming material should be solved from the source. If it is a fully automatic production line, failure to solve this problem will directly cause the production line to stop production.
② Tooling fixture design: If the fixture design is unreasonable, it will lead to low assembly efficiency, and may also lead to inaccurate control of key dimensions. In order to solve the problems caused by the fixture, the following three aspects need to be considered when designing the fixture: First, the benchmark problem, the positioning benchmark of the fixture and the module must be consistent to avoid the accumulation of tolerances due to different benchmarks; the second is For accuracy issues, the accuracy of the fixture needs to be higher than that of the product to avoid new deviations: the third is the durability issue. The movable or friction parts of the fixture need to be durable and wear-resistant, to avoid the size of the fixture from being loose or worn.
③Detection method: In the work, problems such as inaccurate measurement and low efficiency will be encountered due to improper use of detection tools. In order to avoid problems caused by improper testing tools, it is recommended that you use customized testing tools, which can make testing simple and easy to operate, efficient, and highly acceptable to customers.
Square modules generally use two kinds of glue: one is structural glue, so that the cells are fixed without slippage; the other is thermal conductive glue, which transfers the heat generated by the cells.
Module welding is generally defined as a key process in module production. First, if the poorly welded products flow out, it may cause safety hazards, and secondly, the poorly welded products may cause the module to be scrapped. In actual production, the side seam welding generally uses CMT and laser welding processes, and the connection piece and the battery pole pole welding generally uses laser penetration welding. Because of the difference in the structure of the cell pole, it can be divided into penetration welding, seam welding, butt welding and so on.