Wet-spun PVDF nanofiber separator for direct fabrication of coaxial fiber-shaped supercapacitors

Abstract Coaxial graphene fiber-based supercapacitors have many enticing advantages in terms of large electrode/electrolyte contact interface area, short ion-transport path and high stability, but the polymer electrolyte separators upon which these supercapacitors are based typically lead to high resistance and the risk of short circuit upon severe deformations. To address these challenges, we have developed an efficient and controllable wet-spinning strategy for making poly(vinylidene fluoride) (PVDF) nanofiber separator with modulated thickness to directly fabricate high-performance coaxial fiber-shaped supercapacitors. The porous PVDF nanofiber separator tightly sandwiched in between graphene fiber electrodes featured an interconnected, thin and highly wrinkled network architecture, thereby enabling sufficient chemical reduction of electrode without concomitant destruction of the separator structure, good contact interface, and rapid infiltration and transport of electrolyte ions to the electrode without risk of short circuit. The coaxial fiber supercapacitor made using the wet-spun PVDF nanofiber separator delivered a remarkable specific capacitance of 346.5 mF cm−2 and energy density of 30.8 µWh cm−2, while maintaining high structural toughness and long cycling life (94% retention after 10,000 cycles). This coaxial architectural design with PVDF nanofiber as separator represents a promising strategy to fabricate high-performance fiber supercapacitors for flexible energy storage.