Coaxial electrospun PEG-4000@PVDF composite membranes with intumescent flame retardants: Toward multifunctional fabrics for thermal management and ultra-safe lithium-ion battery separators

• Multifunctional core-shell fiber films were prepared by one-step coaxial electrospinning technique. • Efficient halogen-free synergistic intumescent flame retardant system. • Films exhibit superior phase-change enthalpy, shape stability and flame retardant properties. • Core-shell dual functionality enables simultaneous thermal regulation and flame retardancy for fabrics and lithium-ion battery separators. Phase change materials (PCMs) like PEG-4000 offer high heat storage density and can isothermally store or release energy. However, there are fatal safety problems, such as leakage and flammability during transition, which greatly limit the practical application. To address these issues, coaxial electrospinning was employed to fabricate multifunctional core–shell structured fibers, encapsulating PEG-4000 within a polyvinylidene fluoride (PVDF) shell integrated with halogen-free intumescent flame retardants (IFR). The resulting PEG-4000@PVDF-IFR (PPI) composite fibers exhibit superior thermal stability, shape stability, and flame retardancy. Among them, PPI-3 exhibits a synergistic flame-retardant effect, with a high storage density of 92.26 J g −1 and a V-0 rating in modified UL-94 tests. Compared to PEG-4000, PPI-3 reduces the total heat release (THR) by 51.59 % and increases the char residue from 1.51 % to 15.15 %, significantly enhancing the flame retardancy. The PPI coaxial fiber membrane, featuring a well-designed core–shell structure, combines high porosity, large specific surface area, and superior flexibility, simultaneously enhancing traditional textile comfort and thermal regulation while effectively mitigating thermal runaway risks in lithium-ion batteries. In conclusion, PPI shows considerable potential for application in thermal management applications.