Coaxial core-sheath shaped supercapacitor based on polypyrrole functionalized graphene/carbon nanotubes hollow fibers with ultrahigh length specific capacitance and energy density for wearable electronics

Coaxial fiber-shaped supercapacitors (FSCs) have received considerable attention due to the huge application potential in smart electronics, but their fabrications still remain challenging. Herein, using two polypyrrole functionalized graphene/carbon nanotubes hollow fibers (PPy/GCHF) with different diameters as electrodes, a coaxial FSC with a distinct core-sheath architecture is prepared. The outer scabbard electrode, PPy-750/GCHF 1.0 –8, in three-electrode, depicts a great linear capacitance of 791.9 mF cm −1 at 1 mA cm −1 with a capacity retention up to 93.2 % after 5000 charge–discharge cycles, which obviously exceeds most of the constructed fiber-shaped counterparts. Thanks to this skillful design, the PPy-750/GCHF 0.3 –8//PPy-750/GCHF 1.0 –8 FSC with efficiently shortened ion migration pathway and maximized contact area between gel electrolyte and electrodes shows an excellent linear capacitance of 561.9 mF cm −1 at 0.5 mA cm −1 with a great energy density of 49.9 μWh cm −1 , standing for one of the highest levels in FSCs. In addition, the core-sheath shaped device also affords superior mechanical flexibility and capacitive stability with capacitance retentions of 100–88.7 % from 0 to 120° bending and 84.2 % after 5000 charge–discharge cycles. The good energy storage behaviors and ingenious structure endow PPy-750/GCHF 0.3 –8//PPy-750/GCHF 1.0 –8 to have promising application prospects in wearable electronics.