Ultrathin Polydopamine/BaTiO ₃ Modified PTFE Separator with Synergistic Hydrophilic and Electric Field Regulation toward Stable Zinc Deposition

The high-performance separator with excellent ion transport and zinc deposition regulation capabilities is crucial for enhancing the stability and cycle life of aqueous zinc-ion batteries (AZIBs). In this study, a polydopamine (PDA) and barium titanate (BaTiO3, BTO) modified polytetrafluoroethylene (PTFE) (PDA/BTO-PTFE) separator was fabricated. Specifically, PDA was in situ polymerized into a PTFE nanofiber membrane, and then spontaneously polarized BTO nanoparticles, uniformly dispersed via poly(acrylic acid) (PAA), were incorporated into the PDA treated PTFE membrane by vacuum-assisted filtration. The hydrophilic PDA layer significantly enhances the wettability and electrolyte uptake of the separator and accelerates ion transport. The polarization effect of BTO nanoparticles generates local electric fields, thereby regulating Zn2+ migration pathways and guiding uniform zinc deposition. Meanwhile, the PTFE substrate provides a robust porous framework with an excellent mechanical strength (33.2 MPa), effectively suppressing zinc dendrite penetration. More importantly, the synergistic integration of PTFE, PDA, and BTO constructs a highly efficient three-dimensional Zn2+ transport network (TZn2+ = 0.75), endowing the separator with outstanding electrolyte affinity, ion transport kinetics, and cycling stability. The ZIBs assembled with the PDA/BTO-PTFE separator exhibit excellent cycling stability and interfacial regulation, achieving stable cycling for 2000 h at 1 mA cm–2 and 1000 h at 2 mA cm–2 in symmetric cells. Furthermore, both zinc plating-stripping stability and full-cell capacity retention significantly outperform those of batteries using conventional glass fiber separators. These results highlight the great potential of the PDA/BTO-PTFE composite separator for advanced aqueous zinc-ion battery applications, while also expanding the application scope of PTFE nanofiber membranes.