| Summary: | Transition metal sulfides have excellent electrochemical performance and show great potential for improving the energy density of asymmetric supercapacitors. This study demonstrates a two-step synthesis technique and highlights the enhanced energy storage efficiency of ZnS-NiS<sub>2</sub> composite materials for asymmetric supercapacitors. The composite materials of ZnS nanosheets and NiS<sub>2</sub> nanocrystals are characterized by a rough surface and spherical shape. The sample with the optimal ratio (ZnS-NiS<sub>2</sub>-1:7) exhibits a maximum specific capacitance of 1467.9 F g<sup>−1</sup> (550.5 C g<sup>−1</sup>) at 1 A g<sup>−1</sup>. The specific capacitance of the ZnS-NiS<sub>2</sub>-1:7 sample is 26.1% higher compared to the pure NiS<sub>2</sub> sample. Furthermore, the assembled ZnS-NiS<sub>2</sub>-1:7//AC device shows a high specific capacitance of 127.8 F g<sup>−1</sup> (217.3 C g<sup>−1</sup>) at 1 A g<sup>−1</sup> and an energy density of 51.3 Wh kg<sup>−1</sup> at a power density of 820.8 W kg<sup>−1</sup>. The ZnS-NiS<sub>2</sub>-1:7 sample has exceptional energy storage capability on its own, but it can also be composited with graphene to further increase the specific capacitance (1681.0 F g<sup>−1</sup> at 1 A g<sup>−1</sup>), suggesting promising prospects for the ZnS-NiS<sub>2</sub>-based composite material in the future.
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