Generally, two types of glue are used in module production: one is thermally conductive glue based on thermal conductivity; the other is structural glue that prevents mutual slippage between batteries. In actual production, two-component A and B glues are generally used at present. The following mainly introduces the glue making process with two-component glue
(1) Glue principle and method
In the industry, Glue A is generally the main performance glue, and glue B is to help glue A to cure. Simply put, glue AB does not mix, and the curing time of the glue is very long. Therefore, equipment is required to mix A and B glue together. Then apply it to the specified workpiece. The principle of the gluing equipment is: store and stir the A and B glues, and then pass through the pumps respectively. The two pumps are glued at the set speed until the glue mixing head is mixed, and the glue application head drives the glue application through the worktable.
According to different product design requirements, there are four types of glue dispensing methods: glue dispensing, glue coating, glue spraying and glue filling. Glue is generally used in the welding of wire harness and connecting piece, mainly used to fix the wire harness and prevent welding oxidation; glue is to apply glue according to a certain walking track, which is a relatively common glue between batteries. Method; glue spraying is a form of spraying glue on the surface of the cell under high pressure through a nozzle; glue filling is mainly to pour the weighed glue into the bottom of the electric box to fill and solidify the cell, which is commonly known in the industry as moldless This method will be used in the group plan.
(2) Thermal conductive adhesive parameters and matters needing attention
As the name suggests, thermal conductive adhesives are defined with thermal conductivity as the main performance. In addition to thermal conductivity requirements, curing time, bonding strength, flame retardant grade, aging resistance and other properties must also be considered. For example, a product needs to be coated with thermal conductive glue on the aluminum plate. The thinner the coating of the glue, the better, because the thermal conductivity of general metals is better than that of glue. Another reason for applying less glue is to reduce the quality of the module and appropriately increase the energy density of the module. However, if the coating of the glue is too thin, such as the thickness of the coating <0.5mm, it will reduce the adhesion between the glue and the aluminum plate, so the thickness must be within a reasonable range. According to experience, it is generally appropriate to control the thickness to 0.7~1.2mm.
The aging performance of the glue is also a very critical parameter. As the requirements of customers are getting higher and higher, the mileage and age of the products are getting higher and higher, and the performance requirements of the products are more stringent. If the life of a product is 8 years, if the glue ages after 5 years, the bonding force will decrease sharply, causing the thermal conductive glue to fall off from the aluminum plate, and the aluminum plate and the glue are filled with air, and the heat transfer from the previous contact becomes air. Heat transfer makes the effect and effect of heat conduction worse, which greatly shortens the life of modules and packs, and may even cause the risk of thermal runaway.
The curing time of the glue (also known as the surface drying time) has a great influence on the production. For example, the surface drying time of one glue is 10 minutes, and the surface drying time of the other glue is 30 minutes. If the glue needs to dry on the surface, it can flow normally. Pull, I believe readers have already seen the impact of the two glues on production. If the selected glue is cured by an exothermic reaction, generally the glue is cured from the inside to the outside, and sometimes the inside hardens and the outside sticks to the hands. Heating can make the glue start to solidify at the same time from the inside and outside, which can shorten the curing time and improve the production efficiency
(3) Structural adhesive parameters and matters needing attention
Structural adhesives are based on bonding strength as the main indicator, while curing time, service life, flame retardant grade, and aging resistance must also be considered. The structural glue is mainly used to bond the cells, partitions and end plates together. Depending on the product, the type of glue may be different.