Facile Synthesis of MnO₂/CNTs Composite for Supercapacitor Electrodes with Long Cycle Stability

The MnO2/carbon nanotubes (CNTs) composites were prepared through a modified one-pot reaction process, in which CNTs were coated by cross-linked MnO2 flakes uniformly. The composition, morphology, and microstructure of the products were characterized using TG, XRD, XPS, Raman, FESEM, TEM, and STEM. It reveals that the MnO2 layer stands on the sidewalls of the inner nanotubes uniformly about 50 nm thick, and the loading of MnO2 on the CNTs reaches 84%. Furthermore, the supercapacitive performances were investigated by cyclic voltammogram (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS). The experimental results indicate that the composite exhibits not only high specific capacitance of 201 F g–1 and rate capability (the specific capacitance at 20 A g–1 is 70% of that at 1 A g–1), but also excellent cycle stability (no obvious capacitance decay after 10 000 cycles at 1 A g–1). An asymmetric electrochemical capacitor was assembled by using the obtained MnO2/CNTs composite as positive electrode and activated carbon (AC) as negative electrode. The as-assembled AC//MnO2/CNTs capacitor can cycle reversibly in a voltage of 0–1.5 V and give a high energy density of 13.3 Wh kg–1 at a power density of 600 W kg–1.