Cooperative effect of hierarchical carbon nanotube arrays as facilitated transport channels for high-performance wire-based supercapacitors

It is demonstrated that hierarchical nanostructures can greatly enhance the performances of a wire-based supercapacitor (WS), meanwhile can also increase the WS's volume and further hamper the improvement of the WS's capacitance per unit volume. Here a type of three dimensional hierarchical MnO2@carbon nanotube array (CNTA) composites has been designed on stainless steel wires (SSWs) and the cooperative effects of various parameters (such as MnO2 masses, CNTA lengths and wire lengths) on the electrochemical performances of the wire electrodes are systematically investigated. Results show that the specific capacitance of the electrodes can be optimized by MnO2 masses and array lengths, while independent to wire lengths. Moreover, the optimized MnO2@CNTA/SSW electrodes can exhibit high capacitance (9.1 mF cm−1 at 5 mV s−1), good rate-capability (64.46% at 3 A cm−3), and high cycle retention (84.8% after 1000 cycles). Furthermore, the assembled all-solid state flat symmetrical WSs show desirable capacitive behaviors (∼0.78 mW h cm−3) and good flexibility.