Three-dimensional hierarchical interwoven nitrogen-doped carbon nanotubes/Co_xNi_1-x-layered double hydroxides ultrathin nanosheets for high-performance supercapacitors

Three-dimensional (3D) interwoven nitrogen-doped carbon nanotubes (N-CNTs)/Co_xNi_1-x-layered double hydroxides (Co_xNi_1-x-LDHs) ultrathin nanosheets on Ni foam have been rationally designed via the combination of chemical vapor deposition and electrochemical deposition approaches. The Co_xNi_1-x-LDHs nanosheets are uniformly distributed on the N-CNTs, which can not only serve as the stable frame to improve the specific surface area, but also can enhance the conductivity. The Ni foam/N-CNTs/Co_0.5Ni_0.5-LDHs nanosheets electrode displays a remarkable maximum capacitance (2170 F g^-1 at 1 A g^-1 and 1.62 F cm^-2 at 1 mA cm^-2), excellent rate capability (80.9% specific capacitance retention at 20 A g^-1 and 75.8% areal capacitance retention at 30 mA cm^-2) and good cycling stability. First-principles calculations further reveal that the Co doping can effectively reduce the band gap of Ni(OH)₂ and increase the conductivity. This work demonstrates a facile synthesis strategy of 3D hierarchical Ni foam/N-CNTs/Co_xNi_1-x-LDHs nanosheets electrode with remarkable electrochemical properties, which can be used in energy storage and conversion.