Nanoparticles-Dotted 3D Porous Nanofiber Skeleton Separator for Advanced Supercapacitors

As one of the key components of supercapacitors (SCs), separators can directly affect the energy density, output power, and safety stability of SCs. However, it is still a challenge to prepare separators that simultaneously combine large pore size, ultrathin thickness, and excellent mechanical properties. Herein, a 5 μm ultrathin separator with a three-dimensional (3D) porous nanofiber skeleton dotted by fumed Al₂O₃ nanoparticles has been developed using biaxial stretching. The unique structure of the 3D porous nanofiber skeleton ensures a mechanical strength up to 40 MPa, while the fumed Al₂O₃ nanoparticles dotted on the 3D skeleton and the incorporation of the annealing process achieve a large average pore size of 130.8 nm, thus harmoniously resolving the contradiction between strength and large average pore size for ultrathin composite separators. The ultrathin thickness greatly shortens the ion transmission channel and effectively reduces ion transmission resistance. Moreover, the fumed Al₂O₃ nanoparticles exposed on the surface of the 3D porous nanofiber skeleton enhance the wettability of the electrolyte as well as the thermal stability of the separator, achieving a low bulk resistance of 0.3 Ω and zero shrinkage at 130 °C. Due to the unique structure, UAPFS7 offers a better overall performance compared to commercial separators. These findings indicate that the developed separators exhibit excellent comprehensive performance and have the potential to promote the large-scale application of next-generation energy storage devices.