A proper understanding of silicone in the electric vehicle industry can help you reduce procurement errors, improve product quality and enhance your brand reputation. We offer silicone applications in the electric vehicle industry, the technical parameters and the certifications you need, which can help you purchase the appropriate silicone.
Why Does the Electric Vehicle Industry Need Silicone?
Unlike traditional fuel vehicles, due to the high-voltage system (400V – 800V) and large-capacity battery packs of electric vehicles, new requirements have been imposed on their materials. However, traditional materials have certain limitations. Silicone can meet the new demands.
You can refer to the following table, and you will find that silicone has significant advantages in these aspects:
| Aspect | Limitations of Traditional Materials | Advantages of Silicone |
| Thermal Management | Power devices feature high heat flux; ordinary plastics deliver poor thermal conductivity. | Thermally conductive silicone (1-6 W/m·K) enables efficient heat transfer. |
| High-Voltage Insulation | Prone to breakdown above 6kV. | Dielectric strength reaches 15-20 kV/mm with ample safety margin. |
| Thermal Runaway Safety | Conventional rubber releases toxic fumes when burned. | Ceramic silicone forms an insulating ceramic layer under fire, preventing short circuit propagation. |
| Wide Temperature Range Operation | Most materials fail under temperature variation of -40℃-150℃. | Silicone maintains flexibility stably from -50℃ to 200℃. |
| Long-Term Aging Resistance | Vulnerable to cracking caused by ozone and UV rays. | With a Si-O main chain structure, silicone offers excellent resistance to ozone, UV radiation and weathering. |
5 Applications of Silicone in Electric Vehicles
Battery Pack System
Thermal Management
Thermal management refers to thermal interface materials (TIM), which include products such as thermal pads, thermal gels, thermal structural adhesives and potting compounds.
You can utilize these silicone materials to efficiently conduct the heat generated by the battery cells and modules to the cooling plate or the casing, quickly dissipating the accumulated heat and stabilizing the operating temperature of the devices. This provides thermal protection for EV batteries and power components.
Sealing and Protection
In such applications, you may frequently use silicone foam sealing strips, O-rings and molded seals.
These silicone sealing products can effectively prevent moisture and dust from entering the interior of the battery pack, eliminating short-circuit and moisture damage risks, and ensuring the structural safety of the battery pack. This helps extend the overall lifespan of your vehicle and enhance the brand reputation.
Flame Retardant and Thermal Runaway Protection
In this regard, the main product forms of silicone products are ceramifiable silicone and flame-retardant silicone gaskets, which are mainly used for buffering and isolation between battery cells.
When your customers’ electric vehicle encounters a high-temperature fire, the ceramifiable silicone will solidify to form a dense ceramic protective layer, effectively preventing the spread of the fire. This avoids chain short circuits, not only strengthening the safety barrier for the battery pack, but also providing protection for the personal safety of your customers.
Structural Bonding
Thermal conductive structural adhesive is commonly used for structural bonding and is a type of organic silicone material. It can firmly attach the battery module to the device housing.
Thermal conductive structural adhesive has several advantages when you use it. It possesses excellent thermal conductivity and load-bearing capabilities simultaneously. It can quickly dissipate the heat of the module, withstand long-term structural loads, and also achieve multiple functions such as bonding, heat dissipation, and reinforcement.
High-voltage Connectors and Wiring Harnesses
Electrical Insulation and Sealing
When insulation and sealing are required for the high-voltage connector and wiring harness sections, you may frequently use O-rings, custom seals, and insulating sleeves.
You can use these silicone components in your electric vehicle products. They can effectively prevent high-voltage leakage and are also resistant to corrosion and wear caused by electrolyte.
At the same time, they ensure the overall IP protection level of the machine, preventing water vapor and dust from entering. This guarantees the safety and long-term stability of the electrical operation of your consumer’s vehicle.
High Voltage Cable Jacket
The high voltage cable jacket is usually made of extruded grade silicone rubber. Due to its excellent heat resistance and aging resistance, it is widely used for the protection of high-voltage wiring in electric vehicles.
This silicone material is also very soft, so you can bend it to lay the wires, making it more suitable for your complex installation environment and ensuring the safety of the lines for a long time.
Power Electronic Devices
This section includes inverter, on-board charger (OBC), and direct current-to-direct current (DC-DC), all of which are core components for power conversion. Silicone is typically used as a thermal interface and shock-absorbing filler material in the gap.
You can apply it to IGBT/SiC modules. Silicone can not only transfer the heat of the module to the heat sink, but also buffer vibration and shock. It effectively maintains the operation of the core power components and ensures the quality of your products.
Charging Port
The charging interface part needs to be both sealed and resistant to weather conditions. Therefore, various silicone sealing rings and silicone sealing pads are selected.
Because the silicone sealing rings and silicone sealing pads can prevent rain and dust from entering the interior of your consumer’s electric vehicle equipment and isolate the erosion from the external environment.
When they use the electric vehicle in a -30°C low-temperature environment, since the silicone sealing rings and sealing pads maintain good elasticity and sealing performance, the car can still run stably.
Motor and Electronic Control Vibration Damping
In order to provide your consumers with a good driving experience, it is necessary to do a good job in NVH control. You can choose silicone shock absorber pads and shock absorber sleeves.
By using these silicone components, the high-frequency vibrations of the entire vehicle can be absorbed, reducing the running noise at the source. When your electric vehicle can maintain stable shock absorption and noise reduction performance for a long time, it will reduce the jolting sensation during the driving process for consumers.
How to Choose the Right Silicone for Electric Vehicles?
If you choose the wrong silicone material for an electric vehicle, it may lead to premature sealing failure and poor heat dissipation efficiency, thereby posing potential safety hazards for your consumers during use.
Thermal Management Requirements
Choose the silicone material based on the thermal management requirements. You can make an analysis according to different situations. For example, the general EV power electronic thermal conductivity may only need 1.0–2.0 W/(m·K); while for high-density battery packs and SiC high-temperature modules, we recommend 3.0–6.0 W/(m·K) silicone.
If you also want to consider structural bonding, a thermal conductive structural adhesive with a modulus greater than 7 MPa might be more suitable.
The following table provides the relevant parameters and testing standards of silicone for your reference:
| Parameter | Typical Range | Test Standard |
| Thermal Conductivity | 0.2 – 6.0 W/(m·K) | ASTM D5470 / ISO 22007-2 |
| Thermal Impedance | ＜ 0.5 – 1.5 K·cm²/W | ASTM D5470 |
| Breakdown Voltage | ＞ 6 kV (1mm thickness) | ASTM D149 |
Flame Retardancy Requirements
Based on different demand levels, we have summarized the following selection options and parameter tables for you:
If you only need basic flame retardancy components, silicone parts are sufficient for UL 94 V-1 or V-2 certification. However, if you are using them in EV battery packs or high-voltage components, prioritize UL 94 V-0 and confirm the test thickness. For thermal runaway protection, it is more reliable to directly choose ceramicized silicone.
| Parameter | Typical Requirement | Test Standard |
| Flame Retardant Rating | UL 94 V-0 (Preferred) / V-1 | UL 94 |
| Oxygen Index | > 28% | ASTM D2863 |
| Smoke Density | < 200 | ASTM E662 |
| Heat Release Rate | < 100 kW/m² | ISO 5660 |
Electrical Insulation
| Parameter | Typical Range | Test Standard |
| Dielectric Strength | 15 – 28 kV/mm | ASTM D149 |
| Volume Resistivity | 10¹⁴–10¹⁶ Ω·cm | ASTM D257 |
| Dielectric Constant (1 MHz) | 2.8 – 3.5 | ASTM D150 |
| Arc Resistance | 120 – 240 s | ASTM D495 |
From the above table, you can see that there are multiple reference coefficients for electrical insulation. The main reference standard is dielectric strength.
When the voltage system of your electric vehicle is 400V, the dielectric strength must be greater than 15 kV/mm; while when the voltage system is 800V, a dielectric strength greater than 20 kV/mm is more reliable.
Mechanical and Sealing Performance
The sealing components with different functions have different focuses on the mechanical properties of the silicone.
For example, for static seals like battery cover caps, the emphasis is on the compressive set, while for dynamic seals like connectors, the focus is on the tensile strength. If you need a shock absorption and buffering effect, we recommend using foamed silicone. The elasticity of its recovery is the priority to be examined.
| Parameter | Typical Range | Test Standard |
| Hardness (Shore A) | 20–80 | ASTM D2240 |
| Tensile Strength | 5–12 MPa | ASTM D412 |
| Elongation at Break | 300–800% | ASTM D412 |
| Compression Set | < 20-30% (150°C/22h) | ASTM D395 B |
| Tear Strength | 15–40 kN/m | ASTM D6240 |
Environmental Durability
The aging failure of silicone parts usually occurs due to thermal aging and ultraviolet aging. Therefore, if the silicone parts inside a conventional EV do not come into contact with sunlight, only their temperature resistance and ozone resistance need to be focused on.
However, when your silicone parts are used for charging interfaces, they will be exposed to sunlight for a long time, so in addition to their temperature resistance and ozone resistance, attention should also be paid to their resistance to ultraviolet rays.
| Parameter | Typical Range / Requirement | Test Standard |
| Continuous Operating Temperature | -50°C – 200°C | IEC 60068 |
| Thermal Aging (200°C/72h) | Tensile strength retention ≥ 80% | ASTM D573 |
| Ozone Resistance | No cracks (50pphm/40°C/72h) | ASTM D1149 |
| UV Aging Resistance | Property retention ≥ 90% (1000h) | ASTM G154 |
FAQ
What is Ceramifiable Silicone? Why Is It Used in Electric Vehicles?
In case the car catches fire during driving, the ceramifiable silicone will form a hard ceramic layer under high temperatures (400 – 800°C), which can prevent the fire from spreading and enhance safety.
How Many Years Can Silicone Last in Electric Vehicles?
The expected lifespan of silicone in normal operating conditions of electric vehicles is typically 10 to 15 years. However, if the working environment temperature and humidity are very high, it may shorten the lifespan.
How to Choose Between LSR, HCR and RTV Silicone for Electric Vehicle Applications?
LSR is suitable for making precise connector seals and O-rings; HCR is extrusion molding and is more suitable for manufacturing sealing gaskets, cable sheaths, and shock absorbers. RTV is more used for thermal conductive gels, potting protection, and on-site molding seals.
Why Do Silicone Seals for EV Charging Ports Fail Easily?
Because frequent insertion and removal of the charging port will accelerate wear and tear. When your customer’s electric vehicle is charging outdoors, it will be exposed to ultraviolet rays for a long time, which will accelerate the aging of the silicone.
What Is the Current Status of Silicone Parts Recycling in Electric Vehicles?
Because silicone is a thermosetting material, it cannot be simply melted and recycled like TPE. However, it is possible to incinerate silicone to recover thermal energy, and some chemical processes can also break down silicone into silicone oil and filler materials.
If you are looking for recycled silicone materials in a closed-loop system, it might be some time before they become available.
Final Thoughts
Legensilico is a professional silicone manufacturer in China. We can provide you with high-quality silicone products such as gaskets and sealing rings. If you are interested in our silicone products and want to place an order, please feel free to contact us at any time.
