Free-standing NiCo2S4@VS2 nanoneedle array composite electrode for high performance asymmetric supercapacitor application

Two-dimensional (2D) VS2 nanosheets along the NiCo2S4 needle arrays were prepared via an in situ sulfurization-assisted hydrothermal process. The unique nanostructure and phase were characterized by using field effect scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction. The electrochemical properties were recorded by cyclic voltammetry, charge/discharge curves, and electrochemical impedance spectroscopy. The binder-free NiCo2S4@VS2 electrode has contributed to a high specific capacity of 1023. 4 C g−1 with remarkable stability where 96% of its capacity retained after 2000 cycles at the current density of 0.45 A g−1 due to the synergetic effects. Promoting for practical applications, an asymmetric supercapacitor (ASC) composed of NiCo2S4@VS2 as the positive electrode and activated carbon (AC) as the negative electrode with polypropylene as the separator was fabricated. The assembled ASC contributed to a maximum energy density of 31.2 Wh kg−1 at the power density of 775 W kg−1 with good stabilities under different current densities. Thereby, this rational design provides a new strategy for synthesizing electrode materials for high-performance supercapacitors.