Millimeter‐Long Vertically Aligned Carbon‐Nanotube‐ Supported Co3O4 Composite Electrode for High‐Performance Asymmetric Supercapacitor

Cobalt oxide (Co3O4) nanoparticles uniformly anchored on vertically aligned carbon nanotube arrays (VACNTs) are synthesized by means of an effective supercritical carbon dioxide (scCO(2)) assisted impregnation followed by a thermal annealing process. Benefiting from their desirable 3D nanostructure, the Co3O4/VACNTs (CVN) composites manifest a high specific capacitance of 833Fg(-1) at a current density of 1Ag(-1) and a good rate capacity with capacitance retention of 89% even after 20-fold increase in current density. Coupled with a Fe3O4/VACNTs (FVN) anode (350Fg(-1) at 1Ag(-1)) prepared by the same method, the assembled CVN//FVN asymmetric supercapacitor (ASC) delivers a high energy density of 36Whkg(-1) (1.65mWhcm(-3)) at a power density of 0.93kWkg(-1) (0.05Wcm(-3)), and a maximum power density of 13.6kWkg(-1) (0.62Wcm(-3)) at an energy density of 10.6Whkg(-1) (0.51mWhcm(-3)). Moreover, even after 5000 charge-discharge cycles at a current density of 5Ag(-1), the ASC still retains 87% of its initial specific capacitance. The extraordinary electrochemical performance of the ASC device demonstrates the promise of our VACNTs-based pseudocapacitive electrode for future energy storage systems.