A series of mixed metal sulfides of NixCu1−xCo2S4 were synthesized by a facile two-step hydrothermal method and they were investigated as electrode materials for supercapacitor. A substitutional solid solution can be easily formed due to the same atom occupation and similar crystal radius of Ni and Cu in the metal sulfides. The electrochemical performances of the mixed metal sulfides are strongly influenced by the chemical compositions, though they have the same crystal structure. Among all the as-prepared materials, Ni0.67Cu0.33Co2S4 shows the best electrochemical performances with the highest specific capacitance of 1340.48 F g−1 at 1 A g−1, outstanding rate capability and excellent cycling stability. The improved performances can be attributed to the high crystallinity, modified microstructure, increased electrochemical sites and improved electroconductivity caused by lattice distortion as well as the synergistic effect in the Cu-substituted NiCo2S4. Furthermore, the assembled two-electrode hybrid device Ni0.67Cu0.33Co2S4//activated carbon can deliver a high energy density of 40 Wh kg−1 at the power density of 412.5 W kg−1, showing a great potential for energy storage.
