The Application of Silicone Foam in New Energy Vehicle Power Batteries

Silicone foam material (also known as silicone foam/foamed silicone) is a porous, low-density, and compressible polymer elastomer made from raw materials such as silicone rubber raw gum, fillers, vulcanization accelerators, and foaming agents. After uniform mixing, it is produced through a special process under high pressure and high temperature. Possessing the high elasticity of silicone rubber and the sound insulation and shock absorption properties of foam materials, it finds extensive applications in daily life, often serving as vibration damping pads, sealing gaskets, sound-absorbing materials, insulating layer materials, and thermal insulation materials in the airline industry. According to the cell structure, organic silicone foams are classified into closed-cell, open-cell, and mixed types.

The closed-cell foamed organic silicone foam material exhibits excellent shock absorption, buffering, sound insulation, heat insulation, and flame retardant and explosion-proof characteristics. In the automotive field, it is mainly used for heat-insulating foam pipes in vehicle air conditioners, vehicle shock absorption, and foamed silicone sealing washers for new energy vehicle batteries. Currently, many automotive interior materials, such as floors, ceilings, steering wheels, and car seats, are polyurethane foam materials. On one hand, the technology of polyurethane foam materials is relatively mature, and their performance meets the usage standards; on the other hand, the price of polyurethane foam materials is relatively low. However, polyurethane foam materials have poor weather resistance, are flammable, and release a large amount of toxic gases harmful to the human body during combustion. Therefore, with the promotion of organic silicone foam materials and the improvement of people's understanding of them, it is expected that organic silicone foam materials will replace traditional polyurethane foam materials in the future.

Heat-insulating silicone is a kind of silicone prepared from raw materials such as alkali-free ultra-fine glass wool, room temperature vulcanized silicone rubber, fumed silica, iron oxide, and hydroxyl silicone oil.

The silicone heat-insulating buffer frame product has the functions of buffering and heat insulation and can be applied to the thermal protection field of lithium batteries in new energy vehicles.

Characteristics of silicone foam:

Density of silicone foam.

The density of the silicone foam matrix is 1.17 g/cm³. However, through foaming treatment, the density of the currently prepared organic silicone foam materials in mature processes can be as low as 0.16 - 0.20 g/cm³, which can be used for components such as car seats and headrests; while the conventional silicone rubber foam materials (with a density of 0.45 g/cm³) are widely used for gap filling in sealing and shock absorption parts.

Flame retardant performance of silicone foam.

According to scientific experimental research data, silicone foam with added flame retardants has excellent flame retardant performance, and the flame retardant grade can reach UL94-V0. When applied to electric vehicles, it can effectively reduce problems caused by combustion.

Electrical insulation performance of silicone foam.

With the increase in the amount of physical fillers, the volume resistivity and surface resistivity of silicone rubber tend to decrease, and the dielectric constant and dielectric loss factor generally tend to increase. It can be seen that adding physical fillers damages the electrical insulation performance of silicone rubber to a certain extent.

Application of silicone foam in the electric vehicle industry:

The battery cell is the power source of pure electric vehicles. The potential safety hazards of battery cells seriously endanger the safety of the entire vehicle. When the battery cell is working, it will generate a certain amount of heat. Under different temperatures, it can produce a certain thermal expansion and contraction effect, resulting in the expansion of the battery cell. Long-term capacitive grid friction between battery cells is likely to cause battery cell damage and lead to battery failure, and in severe cases, even out of control. In addition, the output voltage of the battery pack reaches above 200V, and it is required that the battery case must be sealed and waterproof to prevent water ingress and short circuits. The waterproof grade of the battery case is required to reach IP67.

Silicone foam has high compression-recovery characteristics, preventing deformation caused by the thermal expansion and contraction of battery cells during the charging and discharging process. It has excellent durability, low compressibility, shock absorption, and flame retardancy (UL 94 V0 grade). At the same time, silicone also has good waterproof performance and the following properties, so it is widely used in the buffer heat insulation and frame sealing of new energy battery cells.

Under different temperatures, the performance of silicone foam is stable, and the performance of product sealing rings is stable.

Excellent waterproof sealing, ensuring no water ingress when the product is used outdoors.

Low long-term compression loss, having a certain ability to resist compression deformation.

Excellent flame retardant performance, effectively preventing risks caused by the thermal effect during battery operation.

The thickness and hardness can be designed according to different standards. The sealing ring must match the housing well and have low stress, effectively preventing the sealing ring from bending and bulging.

The working principle of using thermally conductive silicone sheets in new energy vehicle lithium batteries: Since the temperature difference within the battery pack is not controlled within 5°C, a thermally conductive silicone sheet needs to be attached to both the top and bottom of the battery pack. The thermally conductive silicone sheet then directs the temperature to the outer aluminum shell, controlling the temperature difference of the entire battery module within 5°C, meeting the design requirements of the battery pack, thus prolonging the service life of the battery pack and making the performance more stable during driving.

Between batteries and between batteries and pipes, filling thermally conductive silicone sheets with good electrical insulation and thermal conductivity can play the following roles:

Changing the contact form between the battery and the heat dissipation pipe from line contact to surface contact;

Helping to increase the temperature between single batteries;

Helping to increase the overall heat capacity of the battery pack, thereby reducing the overall average temperature.