New energy vehicles are a mainstream trend to solve energy, environment, urban transportation, and other issues, and also a major direction for the future development of the automobile industry. However, how far China's new energy vehicles can go depends on how far the power battery can go. As the core of new energy vehicles, power batteries are the key to improving cruising range and vehicle performance.
At present, the most powerful batteries are lithium-ion batteries. However, in the case of charging and collision, lithium-ion batteries can easily cause a chain exothermic reaction and cause thermal runaway, resulting in serious accidents such as smoke, fire, and even explosion. And the performance of the power lithium battery pack, including energy density, service life, discharge rate, etc., is greatly affected by temperature, and many heat-generating components require strict thermal management, such as batteries, heat sinks, electronic controls, motors, entertainment systems, thermal pad, etc. The heat needs to be dissipated in time to avoid damage to electronic components and the risk of fire from overheating the battery. Therefore, power battery thermal management technology is one of the core technologies of new energy vehicles.
- What effect does the filler have on the cracking resistance of the potting adhesive?
- What effect does the filler have on the thermal conductivity and mechanical properties of potting adhesives?
- How the flame retardant dosage affects the performance of potting adhesives?
- How do coupling agents affect the performance of potting adhesives?
Why can thermal conductive encapsulants better dissipate heat?
The thermal conductive materials currently used in the vehicle thermal management system include thermally conductive silicones sheets, thermally conductive insulating materials, thermally conductive potting glue, and thermally conductive gap filling material.
Among them, the thermal conductive potting compound is a kind of silicone thermally conductive material that is widely used in new energy electric vehicles. It can form a soft, elastic silicone elastomer with adhesion on the surface through addition curing reaction at room temperature, and thermally conductive silicone rubber elastomer with excellent electrical insulating properties. In the traditional automotive field, thermally conductive silicone encapsulant has been widely used in electronic power modules, high-frequency transformers, connectors, sensors, etc. It not only provides good thermal conductivity but also has the functions of insulation, filling, protection, etc.
The thermal conductivity potting compound can be used as a heat dissipation material to transfer heat because it has a higher thermal conductivity than air. The thermal conductivity of air at 20°C is 0.0267W/(m. K), and the excellent thermal conductivity of potting compound can be optimized by formula. The thermal conductivity of the electrical device can be transferred out at a faster rate.
This is like in hot summer, jumping directly into the water and soaking is obviously faster than the fan blowing, because the water completely surrounds the human body, and the heat can be transferred through heat sink from the body faster than air with a very small thermal conductivity -- while encapsulant is the process of filling the air space around an electronic device with a liquid polymer system (usually two components). (Dark blue part of the picture below)
Grey and black represent two different surfaces, light blue represents air and dark blue represents thermal interface material. When the surfaces of two objects are in contact with each other, it is impossible to completely and closely contact each other, because the surfaces of the objects will have roughness, and there will always be some air gaps mixed in them, and the thermal conductivity of air is very small, so it will cause higher contact thermal resistance. The use of soft and plastic thermal interfaces material in prefabricated thermal pads can fill this air gap as much as possible, reduce the contact thermal resistance, and improve the heat dissipation performance.
Factors Affecting Thermally Conductive Potting Compounds
Taking into account the actual working conditions of the motor, the potting compound used must have high thermal conductivity, good fluidity, crack resistance, and strong adhesion. This causes the problem of the high energy consumption ratio of automobiles.
The potting materials suitable for electronic components and power battery modules in electric vehicles can be divided into epoxy resin potting; silicone rubber potting (silicone potting); polyurethane potting. Let's take epoxy resin potting glue as an example to see what factors affect the performance of potting glue.
What effect does the filler have on the cracking resistance of the potting adhesive?
The epoxy resin will shrink to a certain extent during the curing process. Suppose the pure epoxy resin is used for motor potting when the stress generated by the curing shrinkage of the potting glue is greater than the bonding force between the potting glue and the casing. In that case, it will When the stress generated by the curing shrinkage of the potting glue is less than the bonding force between the potting glue and the casing and the strength of the potting glue is poor, the cracking of the potting glue will be caused. Therefore, in order to avoid these phenomena, it is necessary to reduce the curing shrinkage of the potting glue and increase the strength of the potting glue, and adding a certain amount of filler to the potting glue can effectively reduce the curing shrinkage of the potting glue.
However, the amount of filler added should not be too much or too little. If the amount of filler is too small, the curing shrinkage of the potting glue is high. Although adding too much can continue to reduce the curing shrinkage of the potting glue, with the increase of the filler, the viscosity of the potting glue will also increase significantly.
What effect does the filler have on the thermal conductivity and mechanical properties of potting adhesives?
Generally, the most used filler for thermal conductivity is Al2O3; and the high thermal conductivity is mostly metal nitride, such as SiN, AlN is more commonly used. The thermal conductivity of thermally conductive materials is not only related to the thermally conductive filler itself, but also closely related to the particle size distribution, morphology, interfacial contact, and the degree of bonding within the molecule. Generally speaking, the thermal conductivity of fibrous or foil-like thermal conductive fillers is better. In addition, the thermal conductivity of potting adhesives formulated with fillers of different particle size compounding is also better. This is because a single particle size of filler particles can not well form a continuous thermal conductivity channel inside the potting adhesive, there is a gap between particles and particles, and between different particle sizes of filler particles, a small particle size filler can well compensate for the gap generated between large particles of filler, forming a complete thermal conductivity channel to achieve a better heat transfer effect.
How the flame retardant dosage affects the performance of potting adhesives?
The addition of flame retardants can improve the flame retardant properties of potting adhesives, currently, the use of aluminum hydroxide and magnesium hydroxide is the main focus. However, when using a single aluminum hydroxide or magnesium hydroxide as a flame retardant, the flame retardant effect is not as good as when using a combination of flame retardants. Furthermore, the use of compounded flame retardants results in a lower viscosity of the potting compound.
The reason why the flame retardant effect is better when used in combination is probably that the decomposition temperature of aluminum hydroxide is about 250°C and the heat absorption is 1965 J/g, and the decomposition temperature of magnesium hydroxide is above 300°C. They both have good flame retardant performance and their flame retardant mechanism is mainly dehydration and heat absorption. When the temperature reaches the decomposition temperature of aluminum hydroxide, first of all, aluminum hydroxide will absorb a lot of heat to play a flame retardant effect, when the temperature rises further, magnesium hydroxide to remove water will also play a certain flame retardant effect, so the use of the two 1:1 compound can reduce the amount of flame retardant filler, which also ensures that the automotive motor in the operation of abnormal conditions when the colloid does not fuel.
How coupling agents affect the performance of potting adhesives
Appropriate viscosity can increase the fluidity of the potting compound, improve the defoaming ability, improve the anti-settling ability of the filler in the potting compound, and, as a result, ensure the stability of the product. The addition of a coupling agent can effectively solve the above problems. According to research, in the process of mixing resin and filler, the viscosity of the resin will decrease with the increase of the silane coupling agent in a certain range until it becomes stable.
In addition, the surface treatment of the thermally conductive filler can also improve the thermal conductivity of the filler. By using its compatibility with the base glue and increasing the filling amount, the thermal conductivity of the encapsulant can be greatly improved. For example, RTV thermal conductive silicone rubber is filled with corundum powder surface-treated with silane coupling agents KH-550, A-151, hexamethyldisilazane, dimethyldimethoxysilane, and the thermal conductivity of the material can be adjusted from 1.16w/(m. K) to 2.10w/(m. K), and the thermal conductivity is nearly doubled.
XJY Silicones - First choice raw material supplier of silicone thermally conductive materials
XJY Silicones, one of China's leading Silicone MQ resin and VMQ thermally conductive silicones manufacturers, has 30+ years of R&D and manufacturing experience and 15+ related patents and technical assistance in the silicone industry, also can customize the cost-effective thermally conductive silicone products according to the requirements of your electronic applications.