Mesostructured Carbon Nanotube-on-MnO₂ Nanosheet Composite for High-Performance Supercapacitors

Carbon nanomaterials have been widely used to enhance the performance of MnO₂-based supercapacitors. However, it still remains a challenge to directly fabricate high combining strength, mesostructured and high-performance MnO₂/carbon nanotube (CNT)-nanostructured composite electrodes with a little weight percentage of carbon materials. Here, we report a novel mesostructured composite of the CNT-on-MnO₂ nanosheet with a high MnO₂ percentage, which consists of vertically aligned MnO₂ nanosheets with nanopores and in situ formed oriented CNTs on MnO₂ nanosheets (tube-on-sheet). The optimized CNTs/MnO₂ possesses favorable features, namely, vertically aligned nanosheets to shorted ion diffusion path, a hierarchical porous structure for increased specific surface areas and active sites, and in situ formed CNTs for enhanced conductivity and robust structural stability. It is found that the unique tube-on-sheet CNTs/MnO₂ nanocomposites with the high MnO₂ percentage (>90 wt %) exhibit a high specific capacity of 1131 F g^-1 based on total electrodes and 1229 F g^-1 based on MnO₂ at a current density of 1 A g^-1, high rate capability, and ultrastable cycling life (94.4%@10 000 cycles). This electrode design strategy in this paper demonstrates a new way for high-performance electrodes for supercapacitors with high active material percentage.