Ultrathin manganese dioxide nanosheets grown on partially unzipped nitrogen-doped carbon nanotubes for high-performance asymmetric supercapacitors

•PU-NCNTs were porous and defect-rich.•PU-NCNTs were used as a negative electrode material for supercapacitors.•PU-NCNTs were selected as the substrate for growing ultrathin MnO2 nanosheets.•ASCs were fabricated to enhance the electrochemical performance.

In this work, N-doped carbon nanotubes (NCNTS) have been easily unzipped using a chemical oxidation method to obtain porous and multi-defective partially unzipped N-doped carbon nanotubes (PU-NCNTs), which are promising as negative electrode materials for supercapacitors and are also suitable substrate materials for the efficient loading of ultrathin manganese dioxide (MnO2) nanosheets. Herein, the PU-NCNT/MnO2 composite was synthesized through a simple microwave irradiation method. Moreover, we have fabricated an asymmetric supercapacitor (ASC) using PU-NCNT/MnO2 composite as cathode, PU-NCNTs as anode and neutral aqueous Na2SO4 as electrolyte. Because of the synergistic effects of the PU-NCNTs electrode and the high capacitance as well as good rate performance of PU-NCNT/MnO2 composite, the asymmetric cell exhibited good electrochemical performance. The optimized ASC can be worked stably in the voltage window of 0-1.8 V and exhibited a maximum energy density of 14.76 Wh kg−1 at the current density of 1 A g−1. Additionally, the PU-NCNT/MnO2//PU-NCNT ASC exhibited long cycling stability with 80.5% specific capacitance retained after 1000 cycles at a current density of 1 A g−1. These encouraging results show that PU-NCNT/MnO2 could be promising materials for commercial use of supercapacitors.

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