ZIF-67 derived amorphous CoNi2S4 nanocages with nanosheet arrays on the shell for a high-performance asymmetric supercapacitor

In this paper, unique amorphous bimetallic sulfides of CoNi 2 S 4 with nanocage structure were synthesized. The ZIF-67 with typical rhombic dodecahedron structure was first synthesized, and then the bimetallic product was achieved by the ingenious combination of Ni 2+ -induced template scarification of the synthesized ZIF-67 and the sulfuration reaction. The characterization assays showed that the CoNi 2 S 4 nanocages perfectly inherited the rhombic dodecahedral morphology of the ZIF-67, but with many vertical aligned nanosheets on the shell. The CoNi 2 S 4 nanocages were utilized as an electrode material for capacitance test. The results revealed that the synthesized CoNi 2 S 4 nanocages have low charge-transfer resistance, and high specific capacitance of 1890   F   g −1 at a current density of 4   A   g −1 . The specific capacitance remains 89.9% and 71.6%, respectively after 1000 and 5000 cycling charge-discharge measurements. This excellent performance can be ascribed to the amorphous nature, unique hollow nanocage structure and bimetallic composition of the product. Furthermore, an asymmetric supercapacitor was assembled using CoNi 2 S 4 nanocages as positive electrode materials and Yolk-Shell carbon spheres (YS-CS) as negative electrode materials, and the resulting CoNi 2 S 4 //YS-CS device exhibits a high energy density of 35   Wh   kg −1 at a power density of 640   W   kg −1 .