Flexible supercapacitors based on carbon nanotube-MnO2 nanocomposite film electrode

Abstract Rapid development of wearable electronics has created tremendous demand for miniature energy storage devices with many different architectures. Ideally, very large area high-performance electrode materials are continuously produced at high speed, which are later constructed into flexible supercapacitors of different shapes and sizes. Here we report the synthesis of very large area MnO2 nanosheets on a 10 µm thin carbon nanotube film using a facile hydrothermal reaction. The strong and flexible CNT-MnO2 nanosheet composite film demonstrates excellent faradaic pseudocapacitance when used as electrodes for flexible supercapacitors that can be reconfigured from planar supercapacitor to stretchable threadlike supercapacitors. A narrow strip of the CNT-MnO2 electrode can also be scrolled and twisted together with a negative electrode fabricated by synthesizing FeSe2 nanonuts on a carbon fibre to construct a novel coaxial yarn asymmetric supercapacitor. This architecture has shown a very high energy density up to 27.14 Wh kg−1 at a power density of 571.3 W kg−1 and a good capacity retention after 8000 galvanostatic charge-discharge cycles, together with excellent flexibility and long lifespan.