Development of aqueous asymmetric supercapacitors (ASCs) is often limited by low specific capacitance of negative electrodes. Herein, a composite electrode with tiny vanadium pentoxide (V2O5) nanoparticles homogeneously decorated in vertically-aligned carbon nanotube arrays (VACNTs) is prepared by super-critical CO2 impregnation and subsequent annealing, and used as binder-free negative electrode for aqueous ASCs. Owing to its unique three-dimensional (3D) hierarchical nanostructure, the V2O5/VACNTs (VN) electrodes exhibit an ideal specific capacitance of 284 F g(-1) in the potential range of -1.1 to 0 V vs SCE at 2 A g(-1) and outstanding cycling stability in the Na2SO4 aqueous solution. An aqueous ASC device possessing wide potential range of 1.7 V was constructed with pure VACNTs and VN-350 as the positive and negative electrodes, respectively. The ASC delivers a high energy density of 32.3 Wh kg(-1) at a power density of 118 W kg(-1) and satisfactory cycling life with capacitance retention of 76% after 5000 cycles. (C) 2020 Elsevier Inc. All rights reserved.