introduction to the basics of thermal glue -Lithium - Ion Battery Equipment

Power lithium ion battery pack process series -introduction to the basics of thermal glue -Lithium - Ion Battery Equipment

There are more and more shortcomings exposed by simple mechanical assembly methods, and cannot meet the requirements of continuous improvement of power lithium batteries. The adhesive assembly or assembly is made up for the lack of mechanical assembly. The types of adhesives used in power lithium batteries include structural adhesives, heat conductive adhesives, solder joint protection glue and sealing, and so on. Adhesives are used to improve the performance and safety of power lithium batteries and use them in multiple aspects. The purpose of glue is generally divided into 4 categories: fixed, heat transfer, flame retardant, shockproof, and the specific use forms of glue such as pads, irrigation, filling, etc.

Start with the basic characteristics of thermal conductivity today.

In the heat design, the problem of balance between battery filter power and heat and heat dissipation ability is often considered. The performance of lithium -ion batteries is extremely sensitive to temperature, obtaining appropriate working temperature, which is of great significance for giving full play to battery performance and maintaining reasonable battery life. Reasonable choice of heat transfer media must not only consider its heat transfer ability, but also take into account the process of production, maintain operating, and excellent cost -effectiveness. Speaking from the principle.(Lithium - Ion Battery Equipment)

Why does the thermal conductivity conduct heat

Thermal conductivity is composed of resin matrix [EP (epoxy resin), silicon and PU (polyurethane), etc.] and heat -conducting fillers. The types, dosage, geometric shapes, particle size, mixed filling and modification of thermal conductivity have effects on the thermal conductivity of thermal conductivity. The thermal conductivity of thermal conductivity: The internal thermal carrier of the solid is electronics and sound (in the dielectric, the heat conduction is achieved by the vibration of the lattice. The energy of the lattice vibration is quantum. Quantum is called Shengzi). There is a large amount of free electron inside the metal. It can pass heat through the collision between electrons; inorganic non -metallic crystals by arranging neatly arranged grain heat vibration heat conduction, usually described by the concept of sounds. The extremely fine crystal, so the non -crystal thermal conductivity can also be analyzed with the concept of sound, but its thermal conductivity is much lower than that of the crystal; most polymers are saturated systems and no free electrons exist. It is an important way to improve its thermal conductivity. The heat conduction fillers are scattered in the resin matrix, and each other contacts each other to form a thermal conductivity, so that the heat can be transmitted quickly along the thermal conductivity network, thereby achieving the purpose of improving the thermal conductivity of the adhesive.

What are the forms of thermal conductivity?

In order to suitable for various environments and requirements, there are proper countermeasures for possible thermal conductivity problems. There are many types of subdivisions of thermal conductivity. This is not limited to the application scenarios in the power lithium battery system.

1) Phase change thermal insufficiency materials use the characteristics of the substrate to change in the working temperature, so that the material is more fitted with the contact surface, and at the same time, it also obtains ultra -low thermal resistance. Module gaps pass heat to the outside of the module.

2) Heat conductive conductive pad

High -heat conduction capacity and low -resistant thermal conductivity are generally used inside the electrical appliances. Its thermal conduction capacity and the flexibility of the material itself, which well fit the heat dissipation and installation requirements of the power device.

3) The bonding between the thermal conductive tape on the heat of the heating device and the radiator can achieve thermal conductivity, insulation and fixed function at the same time, reduce the volume of the equipment, and is a choice to reduce the cost of the equipment.

4) The good thermal conductivity and high -level resistance of thermal conductivity and elastic rubber are in line with the current demand for thermal conductivity in the electronics industry. It is the best product to replace silicon fat thermal cream plus cloud -mother tablets. The installation of this type of product is convenient, which is conducive to automated production and product maintenance. It is a new material with processability and practicality.

5) Flexible thermal pads have a thicker heating pad. It is produced specifically for the use of gaps to transmit heat in the design method. Sealing and other uses, this is very suitable for the application of the battery module. 6) Thermal -conducting filling can also be used as a thermal conductivity. It not only has the effect of thermal conductivity, but also a bonding and sealing and sealing material. By filling the contact surface or tank -shaped body, the heat of the heating parts is transmitted. The cylindrical battery module is a typical application.

7) Thermal conductivity insulation and sealing glue Thermal insulation and sealing glue is suitable for irrigation of electronic components with high heat dissipation requirements. After the glue is cured, the thermal conductivity is good, the insulation is excellent, the electrical properties are excellent, the adhesive is good, and the surface is shiny. However, if the amount of glue is too large, the energy density of the battery pack will be pulled down.

What are the factors that affect the performance of thermal glue

The thermal conductivity of the filling adhesive depends on the resin matrix, thermal conductivity and the interface formed by the two, and the types, dosage, particle size, geometric shapes, mixed filling and surface modification of thermal fillers will be Performance affects.

1) Types and dosage of heat -conducting filler

The types and dosage of the filler will affect the thermal guidance rate of adhesives. When the fillers are small, the fillers are completely wrapped by the substrate resin, and the vast majority of filler particles cannot be directly contacted; at this time, the adhesive matrix becomes the heat flow disorder between the filler particles, which inhibits the transmission of the sound of the filler. Therefore What kind of fillers cannot significantly increase the thermal guidance of adhesives. As the amount of fillers is added, the filler gradually forms a stable thermal conductivity in the substrate. At this time, the thermal conductivity increases rapidly, and the filling of high thermal guidance fillers will be more conducive to improving the thermal conductivity of the adhesive. However, too much thermal guidance rate of fillers is not conducive to the improvement of system thermal guidance. Studies have shown that when the ratio of the heat guidance of the filler and the substrate resin exceeds 100, the heat guidance rate of the composite material is not significant.

The data displayed in the previous research instance is used to illustrate the relationship between the amount of filler and heat transfer. After adding high heat -conducting fillers to the adhesive, the thermal conductivity of the composite material has been significantly increased with the amount of filler. Studies show that when W (artificial diamond SD) = 20%(related to the quality of epoxy resin EP), the thermal conductivity is 0.335W (/mk); when W (SD) = 50%, the thermal conductivity rate For 1.07W (/mk), it is 3.5 times higher than the pure resin; when W (SD) <20%, the thermal conductivity of the system is slowly increased; when W (SD)> 20%, the thermal conductivity of the system Quickly rise. This is because when W (SD)> 20%, the particles begin to contact each other and gradually form a thermal conductivity; when W (SD) = 50%, a large amount of contact between particles is improve.

2) The particle size and geometric shape of the thermal filler

When the amount of fillers is the same, nanoparticles are more conducive to increasing the thermal guidance of the adhesive than micron particles. The quantum effect of nanoparticles increases the number of crystal boundaries, which increases the increase in heat capacity and the common price keys into metal bonds, and heat conduction from molecular (or lattice) vibration to free electronic heat transmission, so the thermometer of nanoparticles is relatively relative Higher; at the same time, the particle size and number of nanoparticles are small and large, resulting in a larger surface area, and it is easy to form an effective thermal conductivity in the substrate, so it is conducive to increasing the thermal conductivity of the adhesive. For micron particles, large -particle -size heat conductive fillers with the same amount of fillers are smaller than the surface area, and it is not easy to be wrapped by adhesives.

It is conducive to the increase in thermal guidance of adhesives. A specific case, research shows that when the amount of filler is the same, the thermal conductivity containing the 30nm Al2O3 system is relatively the highest, including the heat guidance rate of the AL2O3 system of 20 & mu3, and the thermal conductivity of the AL2O3 system containing 2 & mu3 system Relatively lowest. This is because when the amount of fillers is the same, the size of the nanoparticles is larger than the micron particles, and the large probability of forming the heating network is higher than the micron particles; for the AL2O3 filling system of 20, 2 & mu; M. The diameter has a large comparison surface area, and there are more interfaces that are in contact with the matrix, which is easier to be wrapped by the substrate and cannot form an effective thermal conductivity.

When the amount of fillers is the same, the possibility of the same fillers of different geometric shapes in the substrate is different. The heating filler with a large diameter ratio is more likely to form the thermal conductivity, which is more conducive to improving the thermal conductivity of the substrate. Above, research shows that when & phi; (nano -level silver line) = 26%(related to the volume of epoxy resin EP adhesives) reaches the inflow threshold, the heat guidance rate increases from 5.66W (/mk) to 10.76W (/mk) (/mk) to 10.76W ( /mk); when & phi; (nano -level silver rod) = 28%, & phi; (nano -level silver block) = 38%reaches the inflow threshold; the larger the long diameter than the infiltration threshold, the smaller. Compared with silver rods and silver blocks, the long -diameter silver wire is added due to its orientation to form the probability of forming thermal network chain in the resin system. When the filler is less, it can reach a higher thermal conductivity.

3) Mixed fill in thermal filler

Compared with the filling system of a single -particle size, mixed filling of different particle size and the same type of filler is more conducive to improving the thermal guidance of the adhesive. The mixed filling of the same type of fillers is easier to obtain a high thermal guidance than a single spherical filler filling. When different types of fillers are properly paired, mixed filling is also better than a single type of filler filling. This is because the above mixed filling is more likely to form a tight accumulation structure, and the high -length diameter is easy to use between the spherical particles during mixed filling, thereby reducing the thermal resistance of the contact, thereby making the system relatively higher and relatively higher Thermal guidance rate. Studies have shown that when w (aln) = 80%(related to the quality of silicone rubber), the particle size is 15, 5 & mu; Aln's total dosage unchanged, two particle size pieces

When the granularity ratio is 1: 1, the thermal guidance rate of the system is 1.85W (/mk). The size of the size of the size is higher than that of a single particle size. This is because when the size of the size is doped, the particles of the small particle size are easier to fill in the gap of the large particle size particles (increase the density increase) to make the particles of the particles. The contact between the intercourse is more closely, and the arrangement density of the filling inside the substrate increases (reducing the thermal resistance of contact), which in turn adds the thermal conductivity of the system.

4) Surface modification of thermal filler

There are polar differences between the interface of inorganic particles and resin matrix, resulting in poor compatibility between the two, so the fillers are easily aggregated into groups in the resin matrix (not easy to disperse). In addition, the larger surface tension of inorganic particles makes it difficult for the surface to be wet by the resin matrix. There are gaps and defects on the phase interface, which increases the interface thermal resistance. Therefore, the surface of the inorganic filler particles can be modified, which can improve its decentralization, reduce interface defects, enhance the intensity of interface adhesion, suppress the scattered scattering of sounds at the interface, and increase the freedom of the transmission of sound, which will help improve the heat of the system. Guidance.



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