A general metal acetate-assisted alcohol thermal strategy to fabricate flexible carbon nanofiber films for supercapacitors†

Flexible carbon nanofiber films (CNFs) have drawn tremendous attention recently due to their fascinating properties. However, CNFs prepared by conventional methods are fragile and easily broken. Therefore, a general approach for synthesizing flexible CNFs is urgently needed. Herein, we report a metal acetate-assisted alcohol thermal (MAA) method for the preparation of flexible CNFs. The MAA is a general and scalable method which can overcome the shortcomings of the pre-oxidation method, and more than 15 different flexible CNFs are successfully prepared. In this method, a polyacrylonitrile (PAN) film is first prepared through an electrostatic spinning process, and then a cyclized polyacrylonitrile (CPAN) film with a high-temperature-resistant trapezoidal structure is formed after MAA treatment. The unique structure of the CPAN will help in maintaining its flexibility to produce a flexible CNF during carbonization at an elevated temperature. To explore their potential in flexible devices, a supercapacitor made of flexible CNF-Zn (the specific surface area is 540 m² g⁻¹; the I_D/I_G ratio is 0.94) is investigated, and it shows an energy density of 11.5 W h kg⁻¹ at 500 W kg⁻¹ and has a capacitance retention rate of 97.2% even after 10 000 charge–discharge cycles. Our findings demonstrate that the MAA method could not only prepare flexible CNFs for energy storage devices, but also has potential application prospects in other fields.