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

Sun, Shumin, Wang, Shen, Li, Shaodan, Li, Yannan, Zhang, Yonghui, Chen, Junli, Zhang, Zhihong, Fang, Shaoming, Wang, Peiyuan
Journal of materials chemistry A 2016 v.4 no.47 pp. 18646-18653
X-ray diffraction, X-ray photoelectron spectroscopy, annealing, capacitance, crosslinking, electrodes, electrolytes, energy density, graphene, hot water treatment, nanoparticles, potassium hydroxide, synergism, transmission electron microscopy
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.