High-performance wearable supercapacitors based on PANI/N-CNT@CNT fiber with a designed hierarchical core-sheath structure

At present, the energy storage performances of fiber supercapacitors are significantly limited by the insufficient charge transfer and defective loading of active materials. Here, to modify the rate capability and cycling stability of flexible fiber supercapacitors, a composite fiber with a hierarchical core-sheath structure is designed by first growing N-CNTs on a highly aligned CNT fiber and then depositing PANI on the N-CNTs. The primary core, highly aligned CNT fiber, ensures free-standing flexibility and the rapid transfer of electrons. The porous primary sheath and secondary core, N-CNTs, can form a framework so as to improve the loading mass and uniformity of the secondary sheath, PANI with high specific capacitance, and enhance the interaction between PANI and the N-CNTs. Moreover, the porous N-CNT structure can simultaneously greatly facilitate the transfer of electrons and ions. The synergistic effects of the CNT fiber, N-CNTs and PANI endow this hierarchical core-sheath structured PANI/N-CNT@CNT fiber with high specific capacitance, excellent rate capability and cycling stability. The specific capacitance reaches 323.8 F g−1 at a current density of 1 A g−1 and 221.3 F g−1 can be retained at a high current density of 50 A g−1. The assembled supercapacitor can maintain 92.1% of the original capacitance after 10 000 charge–discharge cycles at 20 A g−1. Beyond excellent energy storage properties, it also exhibits excellent wearability and flexibility. The capacitance can be maintained at 95.5% after repeated bending processes for up to 10 000 cycles. This work provides a new strategy to develop fiber electrodes for high-performance wearable devices.