Polyacrylonitrile/Polyimide Hybrid Nanofiber Separator for Energy-Dense Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have gained significant attention for large-scale energy storage due to their high safety, environmental friendliness, and cost-effectiveness. However, the lack of high-performance separators remains a major obstacle to their commercialization. In this study, a composite nanofiber membrane composed of polyacrylonitrile (PAN) and polyimide (PI) is fabricated via electrospinning. The PAN/PI composite nanofiber membrane (63 μm-thick) exhibits an average fiber diameter of 431.2 nm, a porosity of 83.9%, an elastic modulus of 24.65 MPa, and a high Zn²⁺ transference number of 0.68. It significantly enhances the cycling stability of zinc-based batteries. Zinc symmetric cells (Zn||Zn) maintain a long cycle life of 2750 h at a current density of 1 mA cm^-2 and a capacity of 1 mAh cm^-2. Zinc-copper asymmetric cells (Zn||Cu) retain an average Coulombic efficiency of 99.3% after 701 cycles. When paired with a Zn_<i>x</i>V₂O₅ (ZVO) cathode, the Zn||ZVO full cell delivers an initial specific capacity of 204.7 mAh g^-1 at 5 A g^-1 and retain 86.9% of their capacity after 1000 cycles. Furthermore, at a discharge current of 0.5 A g^-1, the full cell achieves an energy density of 25.95 Wh L^-1, approximately six times higher than that of conventional glass fiber separator systems.