Hierarchical NiCo₂O₄Nanosheets@halloysite Nanotubes with Ultrahigh Capacitance and Long Cycle Stability As Electrochemical Pseudocapacitor Materials

One-dimensional hierarchical nanostructure of NiCo 2 O 4 nanosheets@halloysite nanotubes was successfully prepared through a facile coprecipitation method followed by a thermal annealing treatment. The microstructure and chemical composition of NiCo 2 O 4 nanosheets@halloysite nanotubes are investigated by SEM, TEM, HRTEM, XRD, and XPS. The specific capacitance of the unique NiCo 2 O 4 nanosheets@halloysite nanotubes is 1728 F g –1 at the end of 8600 cycles when the charge–discharge current density is 10 A g –1, leading to only 5.26% capacity loss. Broadly, the as-obtained NiCo 2 O 4 nanosheets@halloysite nanotubes reveal ultrahigh capacitance and remarkable cycling stability in virtue of the ultrathin and hierarchical nanosheets and intense cation/anion exchange performance of halloysite.