Importance of polypyrrole in constructing 3D hierarchical carbon nanotube@MnO2 perfect core–shell nanostructures for high-performance flexible supercapacitors

Abstract

This study reports the preparation of 3D hierarchical carbon nanotube (CNT) @MnO₂ core–shell nanostructures under the assistance of polypyrrole (PPy). The as-prepared CNT@PPy@MnO₂ core–shell structures show a perfect coating of MnO₂ on each CNT and, more importantly, a robust bush-like pseudocapacitive shell to effectively increase the specific surface area and enhance the ion accessibility. As expected, a high specific capacity of 490–530 F g⁻¹ has been achieved from CNT@PPy@MnO₂ single electrodes. And about 98.5% of the capacity is retained after 1000 charge/discharge cycles at a current density of 5 A g⁻¹. Furthermore, the assembled asymmetric CNT@PPy@MnO₂//AC capacitors show the maximum energy density of 38.42 W h kg⁻¹ (2.24 mW h cm⁻³) at a power density of 100 W kg⁻¹ (5.83 mW cm⁻³), and they maintain 59.52% of the initial value at 10 000 W kg⁻¹ (0.583 W cm⁻³). In addition, the assembled devices show high cycling stabilities (89.7% after 2000 cycles for asymmetric and 87.2% for symmetric), and a high bending stability (64.74% after 200 bending tests). This ability to obtain high energy densities at high power rates while maintaining high cycling stability demonstrates that this well-designed structure could be a promising electrode material for high-performance supercapacitors.