Epitaxial Nanofiber Separator Enabling Folding-Resistant Coaxial Fiber-Supercapacitor Module

Mechanically strengthened fiber-supercapacitors (FSCs) are urgently needed in wearable electronics to adapt frequent severe deformations. However, current bendable FSCs using gel electrolyte as separator are easily shortcircuited under harsh folding due to the limited stretchability of gel polymer. Herein, a folding-resistant coaxial FSC, for the first time, was fabricated through in-situ electrospinning polyacrylonitrile (PAN) nanofibers as separator on fiber electrode, thus effectively avoiding the short-circuit risk under highly localized stretching, compressing and folding. Moreover, such "epitaxial growth "ultrathin (similar to 1 mu m) PAN separator possesses high porosity, favorable strength and seamless contact with fiber electrode, enabling fast ion transport and decreased internal resistance of FSCs. Coupled with robust polyaniline/carbon nanotube (PANI/CNT) composite as model electrodes, our fabricated coaxial symmetric FSC exhibits outstanding structural folding-resistance without electrochemical failure. Amazingly, such in-situ encapsulated separator technique makes it easier to assemble multilayer PANI/CNT electrode in series or parallel. As-assembled coaxial integrated series or parallel device keeps almost same volume as single device, but delivers higher output voltage or capacitance; and simultaneously remains excellent foldable property, showing great practical potential.