Millimeter‐Long Vertically Aligned Carbon‐Nanotube‐Supported Co3O4 Composite Electrode for High‐Performance Asymmetric Supercapacitor
Yaolong Yin; Yong Xu; Yu Zhou; Ya Yan; Ke Zhan; Junhe Yang; Jianqiang Li; Bin Zhao
Index: 10.1002/celc.201800138
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Abstract
Cobalt oxide (Co3O4) nanoparticles uniformly anchored on vertically aligned carbon nanotube arrays (VACNTs) are synthesized by means of an effective supercritical carbon dioxide (scCO2) 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 833 F g−1 at a current density of 1 A g−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 (350 F g−1 at 1 A g−1) prepared by the same method, the assembled CVN//FVN asymmetric supercapacitor (ASC) delivers a high energy density of 36 Wh kg−1 (1.65 mWh cm−3) at a power density of 0.93 kW kg−1 (0.05 W cm−3), and a maximum power density of 13.6 kW kg−1 (0.62 W cm−3) at an energy density of 10.6 Wh kg−1 (0.51 mWh cm−3). Moreover, even after 5000 charge‐discharge cycles at a current density of 5 A g−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.