V2O5 nanosheet arrays/Co3O4 nanoneedle arrays composite for supercapacitor with enhanced energy density

In this work, two-dimensional V 2 O 5 nanosheet arrays/one-dimensional Co 3 O 4 nanoneedle arrays (2D VNSAs/1D CNNAs) composite is successfully prepared on nickel foam substrate. A variety of structural characterization techniques (SEM, XRD, EDS, TEM, and XPS) show that the as-prepared composite is V 2 O 5 monocrystal with a layered structure grafting by Co 3 O 4 polycrystal with a 1D needle-like structure. The VNSAs/CNNAs composite is used as supercapacitor electrode material. In a three-electrodes system, it shows high specific capacitance (C s ) values (1023 F g −1 @5 mV s −1 from CV curve and 826 F g −1 @0.5 A/g from GCD curve), a high coulombic efficiency (98.6 %@10 A/g), a good cyclic stability (92.7 % after 6000 cycles), a low charge transfer resistance (2.7 Ω), and a fast ionic diffusion rate (2.01 × 10 −8 cm 2 s −1 ). In a two-electrodes system, the assembled VNSAs/CNNAs//VNSAs/CNNAs symmetric supercapacitor has C s values of 445 F g −1 @5 mV s −1 and 363 F g −1 @0.5 A/g. Its cycle stability and rate capability could reach up to 92.3 % and 90.7 % after 6000 cycels, respectively. It also shows a high energy density (E d ) of 127.3 Wh kg −1 @400 W kg −1 and can retain 72.2 Wh kg −1 @8000 W kg −1 . The excellent electrochemical properties indicate that VNSAs/CNNAs composite can greatly increase the E d of supercapacitors.