Self-assembled synthesis of waxberry-like open hollow NiCo2S4 with enhanced capacitance for high-performance hybrid asymmetric supercapacitors

Abstract Rational designing microstructure of electrode materials has been regarded as an effective solution for boosting the electrochemical activity. To improve the electrochemical performance of NiCo2S4 for asymmetric supercapacitors (ASCs), a three-dimensional waxberry-like open hollow NiCo2S4 is designed and fabricated via self-assembly by a facile two-step hydrothermal path. The waxberry-like open hollow architecture with rough surface and mesoporous structure can provide abundant edge/surface active sites as well as efficiently shorten the diffusion paths for electrons and ions, thus accelerating the faradaic reactions. By taking advantage of the unique structure and cooperative contributions of nickel and cobalt ions, the waxberry-like open hollow NiCo2S4 delivers a high specific capacitance of 1688 F g−1 (specific capacity of 844 C g−1) at a current density of 1 A g−1 and a capacitance retention of 84.6% after increasing the current density from 1 A g−1 to 20 A g−1. Quantitative analysis of capacitive contribution indicates the fast kinetics of charge storage. Furthermore, the hybrid ASC device assembled with NiCo2S4 and active rice husk carbon as the positive and negative electrodes displays a high energy density of 41.1 Wh kg−1 at power density of 400 W kg−1 under large operating voltage of 1.6 V. These results make the waxberry-like open hollow NiCo2S4 a promising electrode material for high-performance ASCs.