NiCo ₂ S ₄ nanosheets decorated on nitrogen-doped hollow carbon nanospheres as advanced electrodes for high-performance asymmetric supercapacitors

Abstract

Abstract Taking advantage of both Faradaic and carbonaceous materials is an efficient way to synthesize composite electrodes with enhanced performance for supercapacitors. In this study, NiCo 2 S 4 nanoflakes were grown on the surface of nitrogen-doped hollow carbon nanospheres (NHCSs), forming a NiCo 2 S 4 /NHCS composite with a core–shell structure. This three-dimensionally confined growth of NiCo 2 S 4 can effectively inhibit its aggregation and facilitate mass transport and charge transfer. Accordingly, the NiCo 2 S 4 /NHCS composite exhibited high cycling stability with only 9.2% capacitance fading after 10 000 cycles, outstanding specific capacitance of 902 F g −1 at 1 A g −1 , and it retained 90.6% of the capacitance at 20 A g −1 . Moreover, an asymmetric supercapacitor composed of NiCo 2 S 4 /NHCS and activated carbon electrodes delivered remarkable energy density (31.25 Wh kg −1 at 750 W kg −1 ), excellent power density (15003 W kg −1 at 21.88 Wh kg −1 ), and satisfactory cycling stability (13.4% capacitance fading after 5000 cycles). The outstanding overall performance is attributed to the synergistic effect of the NiCo 2 S 4 shell and NHSC core, which endows the composite with a stable structure, high electrical conductivity, abundant active reaction sites, and short ion-transport pathways. The synthesized NiCo 2 S 4 /NHCS composite is a competitive candidate for the electrodes of high-performance supercapacitors.