Highly flexible, freestanding supercapacitor electrodes based on hollow hierarchical porous carbon nanofibers bridged by carbon nanotubes

Supercapacitors are considered to be the next generation of wearable energy storage devices because of reliable safety, high power density, and long cycle life, but the flexibility and energy density limit their practical applications. Herein, the flexible hollow hierarchical porous carbon nanofibers bridged by carbon nanotubes (HPCNFs@CNTs) are designed and constructed, followed by polyaniline (PANI) decorating to fabricate PANI@HPCNFs@CNTs. The synergistic effect of the hollow structure, hierarchical pores, in-situ nitrogen doping, and the bridging structure endows the HPCNFs@CNTs with a high specific capacitance of 461.0F g(-1) (207.4 mF cm(-2)) while maintaining glorious flexibility under various deformation states. Besides, PANI@HPCNFs@CNTs possesses a high specific capacitance of 629.1F g(-1) (405.2 mF cm(-2)) and remarkable cycle stability with 88.5 % capacitance retention after 5000 charging-discharging cycles. The device assembled by PANI@HPCNFs@CNTs renders an ultra-high energy density of 23.3 Wh kg(-1) at a power density of 202.7 W kg (-1). Furthermore, the device provides remarkable cycle stability and high-rate capability with a capacity retention of 91.3 % after 5000 cycles at 5 A g(-1) and 76.7 % at 10 A g(-1), respectively, demonstrating a tremendous potential to construct highperformance flexible energy storage devices.