Directly‐Grown Hierarchical Carbon Nanotube@Polypyrrole Core–Shell Hybrid for High‐Performance Flexible Supercapacitors

A hierarchical carbon nanotube–polypyrrole (CNT–PPy) core–shell composite was fabricated by growing CNTs directly on carbon cloth (CC) as a skeleton followed by electropolymerization of PPy with controlled polymerization time. Direct fabrication of electroactive (CNT–PPy) materials on the flexible CC electrode could reduce the interfacial resistance between the electrode and electrolyte and improve the ion diffusion. The supercapacitor electrode based on optimized PPy/CNT‐CC exhibits excellent electrochemical performance, with the highest gravimetric capacitance being roughly 1038 F g −1 per active mass of PPy and up to 486.1 F g −1 per active mass of the PPy/CNT composite. Notably, excellent flexibility and cycle stability up to 10 000 cycles with only 18 % capacitance loss was achieved. At the same time, the fabricated asymmetric supercapacitor (PPy/CNT‐CC∥CNT‐CC) shows the maximum power density of 10 962 W kg −1 at an energy density of 3.9 Wh kg −1 under the operating potential of 1.4 V. The overall high cycle stability and high performance of the fabricated PPy/CNT‐CC flexible electrode is due to the novel binder‐free direct growth process.