Two-Step Synthesis of ZnS-NiS2 Composite with Rough Nanosphere Morphology for High-Performance Asymmetric Supercapacitors

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-NiS2 composite materials for asymmetric supercapacitors. The composite materials of ZnS nanosheets and NiS2 nanocrystals are characterized by a rough surface and spherical shape. The sample with the optimal ratio (ZnS-NiS2-1:7) exhibits a maximum specific capacitance of 1467.9 F g−1 (550.5 C g−1) at 1 A g−1. The specific capacitance of the ZnS-NiS2-1:7 sample is 26.1% higher compared to the pure NiS2 sample. Furthermore, the assembled ZnS-NiS2-1:7//AC device shows a high specific capacitance of 127.8 F g−1 (217.3 C g−1) at 1 A g−1 and an energy density of 51.3 Wh kg−1 at a power density of 820.8 W kg−1. The ZnS-NiS2-1:7 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−1 at 1 A g−1), suggesting promising prospects for the ZnS-NiS2-based composite material in the future.