Heterostructured NiCo2S4@SnS2 Hybrid for All-Solid-State Supercapacitor Applications: Delocalized Charges on Co–S Heterojunction Improved Electrochemical Kinetics

Heterostructured materials with multiple metal sulfides can improve the performance of supercapacitors by offering enhanced redox-active sites and surface reaction kinetics by facilitating additional ion and electron pathways. Herein, NiCo2S4 (NCS) anchored on SnS2 (TS) nanosheets (i.e., NCS@TS) was prepared using a hydrothermal in situ sulfidation method. Compared to the pristine NCS, the NCS@TS showed 140% capacity enhancement with a specific capacity of 329.22 mA·h/g, a capacity retention of 76.87%, and excellent Coulombic efficiency of 99.77% after 10000 charge/discharge cycles. Density functional theory (DFT) calculations revealed the formation of Co–S covalent bonds due to the interaction of Co (NiCo2S4) and S (SnS2) atoms. The variations in the work functions resulted in an apparent charge transfer from NiCo2S4 to SnS2. Bader charge analysis demonstrated the enhanced charge density on the Co atoms that generated additional redox-active sites in the NCS@TS heterostructure and ultimately enhanced the electrochemical performance. An all-solid-state asymmetric supercapacitor device (NCS@TS//hrGO) was fabricated, which delivered high energy and power densities (106.24 W·h/kg at 1600.27 W/kg and 55.60 W·h/kg at 8006.40 W/kg) with outstanding cyclic stability, proving to be a promising candidate for potential high-performance supercapacitor applications.