Covalently Assembled Black Phosphorus/Conductive C3N4 Hybrid Material for Flexible Supercapacitors Exhibiting a Superlong 30,000 Cycle Durability

Black phosphorus (BP) has been demonstrated as a promising electrode material for supercapacitors. Currently, the main limitation of its practical application is the low electrical conductivity and poor structure stability. Hence, BP-based supercapacitors usually severely suffer from low capacitance and poor cycling stability. Herein, a chemically bridged BP/conductive g-C3N4 (BP/c-C3N4) hybrid is developed via a facile ball-milling method. Covalent P–C bonds are generated through the ball-milling process, effectively preventing the structural distortion of BP induced by ion transport and diffusion. In addition, the overall electrical conductivity is significantly enhanced owing to the sufficient coupling between BP and highly conductive c-C3N4. Moreover, the imbalanced charge distribution around the C atom can induce the generation of a local electric field, facilitating the charge transfer behavior of the electrode material. As a result, the BP/c-C3N4-20:1 flexible supercapacitor (FSC) exhibits an outstanding volumetric capacitance of 42.1 F/cm3 at 0.005 V/s, a high energy density of 5.85 mW h/cm3, and a maximum power density of 15.4 W/cm3. More importantly, the device delivers excellent cycling stability with no capacitive loss after 30,000 cycles.