Innovative Applications of Flame-Retardant Materials in Lithium-Ion Battery Packs

The rapid expansion of electric vehicles and energy storage systems has heightened the need for advanced flame-retardant materials in lithium-ion battery packs. These materials play a critical role in preventing thermal runaway, ensuring passenger safety, and extending battery lifespan. Below are three notable applications of flame-retardant technologies in modern battery systems.

Composite Polymer Materials for Battery Cell Separators

Battery separators are essential components that isolate positive and negative electrodes while allowing ion flow. Traditional polyolefin separators often lack sufficient thermal stability, making them vulnerable to melting or shrinkage during thermal events. To address this, engineers have developed flame-retardant PC/ABS composites, which blend polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) to achieve a balance of mechanical strength, thermal resistance, and flame retardancy.

These composites can achieve UL 94 V-0 flame-retardant ratings, meaning they self-extinguish within 10 seconds after flame exposure. Their high tensile and impact strengths enable them to withstand physical stresses, while their chemical inertness prevents reactions with electrolytes. For instance, in cylindrical battery modules, flame-retardant PC/ABS separators are used as insulating pads to prevent electrolyte leakage and corrosion of battery caps. Their moldability also allows for complex designs, making them adaptable to various battery architectures.

Advanced Coatings for Thermal Runaway Mitigation

Thermal runaway in lithium-ion batteries can lead to catastrophic failures, including fires or explosions. To counter this, researchers have developed flame-retardant coatings that form a protective barrier when exposed to heat. One such innovation involves applying a 1.0 mm-thick coating to battery cells, which delays ignition by over six minutes compared to uncoated cells.

These coatings work through two mechanisms: phase-change heat absorption and carbonized layer formation. When exposed to high temperatures, the coating absorbs heat and transforms into a carbonized layer that blocks oxygen and heat transfer. This technology has been tested on 50 Ah ternary lithium batteries, demonstrating its ability to prevent flames and explosions during thermal abuse conditions. Such coatings are particularly valuable in electric vehicle battery packs, where they can provide critical escape time for passengers in the event of a crash or overheating.

Gel Polymer Electrolytes with Intrinsic Flame Retardancy

Conventional liquid electrolytes in lithium-ion batteries are flammable and prone to leakage, posing safety risks. To improve safety, researchers have developed gel polymer electrolytes (GPEs) with inherent flame-retardant properties. For example, a perfluorinated gel polymer electrolyte (PFGPE) was synthesized by cross-linking perfluorobutyl acrylate (PFBA) monomers with pentaerythritol tetraacrylate (PETEA) crosslinkers.

The PFGPE exhibits exceptional thermal stability and flame retardancy due to two mechanisms: free radical scavenging and carbonized layer formation. During combustion, PFBA decomposes to release fluorine radicals that interrupt the chain reaction of flames. Additionally, the polymer matrix and carbonate-based electrolyte form a phosphorus- and fluorine-rich carbonized layer that further inhibits heat and oxygen transfer. In tests, PFGPE-based batteries demonstrated no flames or explosions when subjected to thermal abuse, unlike traditional liquid electrolyte batteries. This technology also improves battery performance, with PFGPE achieving higher ionic conductivity and Li+ migration numbers at elevated temperatures compared to liquid electrolytes.

Conclusion

The integration of flame-retardant materials in lithium-ion battery packs represents a critical advancement in battery safety technology. From composite polymer separators to advanced coatings and gel polymer electrolytes, these innovations address the thermal vulnerabilities of traditional battery designs. As the demand for high-energy-density batteries grows, continued research into flame-retardant materials will be essential to ensuring the safety and reliability of next-generation energy storage systems.