MnO2 Nanoflake-Shelled Carbon Nanotube Particles for High-Performance Supercapacitors

We introduce MnO2 nanoflake/carbon nanotube (CNT) core–shell particles for high-performance supercapacitors. The CNT particles prepared by drying the CNT-dispersed aerosol produce a tightly intertwined CNT assembly by internal capillary force, and the subsequent growth of MnO2 on the CNT surface produces a high surface area MnO2 nanoflake shell. We control the amount of MnO2 decoration on the CNT particles and obtain a specific capacitance of 370 F/g at current density of 0.5 A/g upon their supercapacitor electrode application. This capacitance is 14 times higher than that of bare CNT particles and 3 times higher than that of bare MnO2 particles. An asymmetric capacitor based on the MnO2/CNT particle is assembled. The capacitor reveals a remarkably high power density of 225 W/kg. This performance is attributed to the contribution of the high pseudocapacitance of a compact MnO2 nanoflake and the high electrical conductivity of CNT particles with compact packing.