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

Abstract

Aqueous zinc-ion batteries (AZIBs), characterized by their safety, environmental sustainability, and cost-effectiveness, exhibit significant potential for large-scale energy storage applications. Nevertheless, the lack of an ideal separator has significantly impeded their practical commercialization. In this work, hybrid nanofiber membranes composed of polyacrylonitrile (PAN) and soluble polyimide (PI) are fabricated through the electrospinning technique. The PAN/PI nanofiber membrane, with a mass ratio of 2:1, demonstrates an average fiber diameter of 431.2 nm, a porosity of 83.9%, and an elastic modulus of 24.65 MPa. The 91-µm-thick PAN/PI nanofiber membrane noticeably enhances the transference number of Zn cations within the aqueous electrolyte, as well as the cycling stability of Zn anodes. When subjected to a charge/discharge current of 2 mA cm⁻² and a capacity of 1 mAh cm⁻², the Zn||Zn cells exhibit cycling capabilities for a duration of 1550 hours, while the Zn||Cu cells achieve 701 cycles, displaying an impressive average Coulombic efficiency of 99.3%. When paired with a ZnxV2O5 (ZVO) cathode, the Zn||ZVO full cells employing the PAN/PI separator exhibit a specific capacity of 204.7 mAh g⁻¹ at a cycling current of 5 A g⁻¹, which retains 86.9% after 1000 charge/discharge cycles. Furthermore, the full cell demonstrates an energy density of 21.74 Wh L⁻¹ at a discharge current of 0.5 A g⁻¹,which is approximately five times greater than that of cells employing a glass fiber separator.

Keywords: aqueous zinc-ion batteries, separator, polyacrylonitrile, polyimide, electrospinning.