Asymmetric supercapacitors based on a NiCo2O4/three dimensional graphene composite and three dimensional graphene with high energy density

Abstract

A NiCo₂O₄ nanoparticle/three dimensional porous graphene (NiCo₂O₄/3D-G) composite was synthesized through a facile hydrothermal method combined with subsequent annealing treatment. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy analyses indicate that the NiCo₂O₄ nanoparticles were tightly anchored on the graphene sheets in the NiCo₂O₄/3D-G composite. When used as a supercapacitor electrode material, the obtained NiCo₂O₄/3D-G displayed a high specific capacitance of 2300 F g⁻¹ at 1.0 A g⁻¹ in 2.0 M KOH electrolyte. The asymmetric supercapacitor utilizing NiCo₂O₄/3D-G and 3D-G as positive and negative electrodes, respectively, delivered a high energy density of 73.8 W h kg⁻¹ with a power density of 800 W kg⁻¹ and long cycle stability (94.3% capacitance retention after 5000 cycles). The excellent supercapacitive performance of the NiCo₂O₄/3D-G can be ascribed to the synergistic effect of the porous and conductive three-dimensional cross-linking 3D-G and the high pseudocapacitive performance of the NiCo₂O₄ nanoparticles.