Characteristics of phosphorus-nitrogen based flame-retardant monomers for UV-curable coatings on battery PET pouches

In this study, photocurable monomers containing phosphorus-nitrogen groups were employed alongside UV curing technology to develop flame-retardant (FR) coatings pouch-type battery cells made from polyethylene terephthalate (PET). Three different monomers were synthesized: a phosphorus-containing urethane acrylate monomer (DUPPO), a phosphorus-nitrogen-containing urethane acrylate monomer (DA-Pi-U), and a phosphazene-containing phenyl methacrylate crosslinker (CP-PMA). These monomers, recognized for their flame-retardant properties, were utilized in binary and ternary coating formulations that were effectively cured via a UV-curing process. The molecular architectures of the synthesized monomers were verified through 1H and 31P nuclear magnetic resonance spectroscopy. The rheological curing behavior of the coating solutions was assessed using an oscillatory rheometer. In addition, the reactivity of the FR coating system was examined via Fourier transform infrared spectroscopy. The thermal and flame-retardant characteristics of the FR coatings were confirmed through thermogravimetric analysis, Raman spectroscopy, limiting oxygen index measurements, and scanning electron microscopy. The ternary FR coating system with CP-PMA exhibited superior thermal stability, flame retardancy, crosslinking density, and mechanical robustness, making it suitable for PET pouches. Furthermore, optimal coating conditions for the slot coating process were determined using a viscocapillary model, enhancing practical applicability in industrial settings.