Nanoparticles-Dotted\n3D Porous Nanofiber Skeleton\nSeparator for Advanced Supercapacitors

As one of the key components of supercapacitors (SCs),\nseparators\ncan directly affect the energy density, output power, and safety stability\nof SCs. However, it is still a challenge to prepare separators that\nsimultaneously combine large pore size, ultrathin thickness, and excellent\nmechanical properties. Herein, a 5 μm ultrathin separator with\na three-dimensional (3D) porous nanofiber skeleton dotted by fumed\nAl<sub>2</sub>O<sub>3</sub> nanoparticles has been developed using\nbiaxial stretching. The unique structure of the 3D porous nanofiber\nskeleton ensures a mechanical strength up to 40 MPa, while the fumed\nAl<sub>2</sub>O<sub>3</sub> nanoparticles dotted on the 3D skeleton\nand the incorporation of the annealing process achieve a large average\npore size of 130.8 nm, thus harmoniously resolving the contradiction\nbetween strength and large average pore size for ultrathin composite\nseparators. The ultrathin thickness greatly shortens the ion transmission\nchannel and effectively reduces ion transmission resistance. Moreover,\nthe fumed Al<sub>2</sub>O<sub>3</sub> nanoparticles exposed on the\nsurface of the 3D porous nanofiber skeleton enhance the wettability\nof the electrolyte as well as the thermal stability of the separator,\nachieving a low bulk resistance of 0.3 Ω and zero shrinkage\nat 130 °C. Due to the unique structure, UAPFS7 offers a better\noverall performance compared to commercial separators. These findings\nindicate that the developed separators exhibit excellent comprehensive\nperformance and have the potential to promote the large-scale application\nof next-generation energy storage devices.