Development of Flame Retarded Battery Casings Using Glass Fiber‐Reinforced Epoxy Resin

ABSTRACT

This study investigates the development of glass fiber‐reinforced epoxy resin composites with enhanced fire performance for application in electric vehicle battery casings. A low‐viscosity epoxy system incorporating phosphorus‐, inorganic‐, and nitrogen‐based (PIN) flame retardants was designed, with particular focus on achieving synergistic effects between ammonium polyphosphate (APP), titanium dioxide (TiO ₂ ) and talcum. A multi‐stage evaluation strategy was applied, including preliminary screening (TGA, LOI, UL‐94, DSC, DMA), followed by detailed characterization of rheological behavior, fire performance under simulated real‐fire conditions (cone calorimetry, glow wire flammability index), and mechanical, electrical, and microstructural properties of the resulting composites. The combination of APP and TiO ₂ exhibited a pronounced synergistic effect, enabling UL‐94 V‐0 classification in reinforced composites at 4 mm thickness. Cone calorimetry revealed a 53% reduction in peak heat release rate, attributed to enhanced char formation and stabilization of the protective layer. Importantly, the incorporation of solid flame retardants with appropriate morphology did not compromise the glass transition temperature (T _g  > 135°C) and resulted in only minor reductions in flexural properties (< 10%), while electrical resistivity remained unchanged. The results demonstrate that the appropriate selection and combination of solid flame retardants enables the decoupling of fire performance from thermomechanical degradation, providing a viable pathway for the development of multifunctional composite materials for fire‐safe battery enclosure applications.