Construction of CoNi2S4 hollow cube structures for excellent performance asymmetric supercapacitors

Although the synthesis of transition metal oxide hollow structures has been relatively perfect, it is extremely challenging to prepare mixed transition metal sulfides with excellent structures and high specific capacitance as electrode materials for supercapacitors. Here, we report a simple ion-exchange method and hydrothermal treatment to synthesize a novel hollow structure of ternary metal sulfide, which is nickel-cobalt sulfide hollow cubes. First, a uniform ZIF-67 (Zeolitic Imidazolate Framework-67) cube is synthesized as a precursor, and then a CoNi2S4 hollow polyhedron is successfully realized through the chemical transformation without annealing. As the electrode materials of supercapacitors, the specific capacitance of the hollow cube CoNi2S4 is 2448 F g−1 at the current density of 1.0 A g−1. In addition, an asymmetric supercapacitor (ASC) device based on CoNi2S4 hollow cubes was also assembled. The asymmetric supercapacitor shows long-term cycling performance with a high energy density of 62.19 Wh kg−1 at the power density of 775 W kg−1. The simple synthesis process, low production cost and excellent electrochemical performance indicate that it has broad application prospects in high-performance electrochemical capacitors.