Phenyl raw rubber (especially phenyl silicone rubber) can effectively solve the flame-retardant sealing problem of new energy vehicle battery packs during thermal runaway due to its excellent high-temperature resistance, flame-retardant properties, and sealing characteristics. This is mainly achieved by forming a stable char layer, inhibiting flame spread, and maintaining seal integrity.

I. Flame-retardant Mechanism of Phenyl Silicone Rubber
* Char Layer Formation Ability
Phenyl silicone rubber can form a high-performance char layer at high temperatures, effectively inhibiting the flame growth rate. Experimental studies show that with the increase of phenyl content, the char products (such as coke) formed by phenyl silicone rubber at high temperatures can significantly reduce the O₂ concentration on the material surface, playing a barrier role. This char layer can effectively wrap the battery cell during thermal runaway, preventing the spread of flames and high-temperature gases to adjacent cells.

Relationship between Phenyl Content and Flame Retardant Properties
*Medium-Phenyl Silicone Rubber (Phenyl content 15~25%): It has characteristics such as ablation resistance and flame resistance. Once ignited, it is self-extinguishing, making it particularly suitable for battery pack sealing applications.

* High-phenyl silicone rubber (phenyl content above 30%): While its main advantage lies in radiation resistance, its flame retardant properties are also significantly superior to ordinary silicone rubber.

Experimental data shows that composite materials with 94 parts of phenyl vinyl silicone rubber added can improve their flame retardant rating from unrated to V0 (UL94 standard), while materials without the addition show no significant flame retardant effect.

II. Sealing Protection During Thermal Runaway
Wide Temperature Range Stability: Phenyl silicone rubber maintains stable performance over a wide temperature range of -100℃ to 350℃, with short-term operating temperatures reaching -110℃ to 400℃. This means that in the early stages of battery thermal runaway (the rapid temperature rise phase), phenyl silicone rubber sealing materials can still maintain structural integrity, preventing electrolyte leakage and the ingress of external air.

Resistance to Thermo-Oxidative Aging: During thermal runaway, the internal temperature of the battery pack rises sharply, causing ordinary sealing materials to age and fail rapidly. Phenyl silicone rubber exhibits excellent resistance to thermo-oxidative aging. Experiments show that the tensile strength change rate of the composite material without phenyl silicone rubber after 48 hours of thermo-oxidative aging is 32.2%, while the change rate of the composite material with 94 parts of phenyl vinyl silicone rubber is reduced to 5.6%. This means that phenyl silicone rubber sealing materials can maintain their function for a longer period during thermal runaway.

Low-Temperature Performance Advantages
In a -75℃ low-temperature tensile test, the tensile strength change rate of the composite material without phenyl vinyl silicone rubber is 118%, while the change rate of the composite material with 94 parts of phenyl vinyl silicone rubber is reduced to 38.6%16. This characteristic ensures that the battery pack sealing system can still operate effectively in cold regions or low-temperature environments, preventing the risk of thermal runaway due to seal failure.

III. Synergistic Effects with Other Safety Technologies
Phenyl silicone rubber sealing materials form a synergistic protection system with other battery pack safety technologies:
* When used in conjunction with aerogel insulation pads, it further blocks heat conduction paths.
* Combined with intelligent thermal response additives (such as mCF₃-BA), it achieves comprehensive protection from the electrochemical to the physical levels.
* As an important component of battery pack structural safety, it meets the requirements of the new national standard GB 38031-2025 for bottom impact, thermal runaway, and high-voltage electrical safety.

IV. Future Development Trends
With the continuous improvement of safety standards for new energy vehicles, the application of phenyl silicone rubber in the field of battery pack safety will become more widespread:
* Research and development of silicone rubber with higher phenyl content further improves flame retardant performance.
* Development of multifunctional composite materials integrates flame retardancy, thermal conductivity, and sealing functions.
* Optimization of intelligent manufacturing processes improves the reliability and consistency of sealing structures.

In summary, phenyl raw rubber, through its unique material properties, provides comprehensive sealing protection for new energy vehicle battery packs, from thermal runaway prevention to thermal diffusion suppression, and is one of the key materials for improving battery system safety. With breakthroughs in domestic technology, this type of material will play an increasingly important role in ensuring the safety of new energy vehicles.