Facile fabrication of foldable electrospun polyacrylonitrile-based carbon nanofibers for flexible lithium-ion batteries

To enable electrospun polyacrylonitrile-based C nanofibers (CNFs) to be employed as anode materials in flexible Li-ion batteries, it is essential to overcome their frangibility and enhance their flexibility. Here, we report a simple method for fabricating free-standing, pure, and foldable CNFs (FCNFs) that involves a novel Zn(Ac)2-assisted electrospinning–peroxidation–carbonization process. Zn(Ac)2 was demonstrated to enhance the uniformity of the peroxidation process by relieving the stress concentration and thereby reducing the fracture of the resulting FCNFs. It also created a porous structure that improved the mechanical strength and flexibility of the FCNFs. Both flexible FCNFs and strong FCNFs, called FCNF-3/4 and FCNF-1/2, respectively, which were fabricated by adjusting the stirring temperature of the spinning solution, exhibited novel multi-folding capacity and excellent elastic-recovery properties and outperformed most state-of-the-art electrospun polyacrylonitrile-based CNFs. In addition, a systematic FCNF flexibility mechanism in which the fabric texture, fiber structure, and microstructure are considered was proposed. When used as a self-supported anode for half-cells, FCNF-3/4 exhibited a discharge capacity of 630 mA h g−1 over 100 cycles with good stability and a high coulombic efficiency, while FCNF-1/2 yielded a better rate performance than FCNF-3/4. Furthermore, a metal-conductor-free foldable full cell consisting of a commercial flexible LiCoO2/CNT cathode and a FCNF-3/4 anode was assembled and was able to light an LED even when it was folded twice. More importantly, the FCNFs proved to be applicable as foldable conductive substrates that are used to load high-capacity active materials (e.g., Si and ZnxCo3−xO4), indicating their high potential to be applied in flexible energy storage devices.