Facial design and synthesis of CoS_x/Ni-Co LDH nanocages with rhombic dodecahedral structure for high-performance asymmetric supercapacitors

In this paper, two-component nanocages containing CoS_x and nickel-cobalt layered double hydroxides (Ni-Co LDH) were facilely synthesized via a multistep transformation approach. The zeolitic imidazolate framework-67 (ZIF-67) nanocrystals were firstly synthesized, and then after partial sulfuration, the CoS_x/Ni-Co LDH nanocages were achieved by adding nickel ions for etching and precipitation. The prepared CoS_x/Ni-Co LDH nanocages consisted of the hollow rhombic dodecahedral morphology with many nanosheets arrays on the shell. When used as electrode materials for electrochemical capacitors, this CoS_x/Ni-Co LDH nanocages deliver a specific capacitance of 1562 F g⁻¹ at a current density of 1 A g⁻¹. In addition, an asymmetric supercapacitor assembled with CoS_x/Ni-Co LDH as cathode and active carbon (AC) as anode shows a high energy density of 35.8 Wh kg⁻¹ at a power density of 800 W kg⁻¹ and has an excellent cycling performance with the retention rate of 94.56% after 10,000 cycles, suggesting their potential application in high-performance electrochemical capacitors. These exceptional electrochemical properties can be attributed to the unique structure and synergistic effects between the metal sulfide and the bimetallic hydroxide, which also indicate the potential application of CoS_x/Ni-Co LDH nanocages in high-performance supercapacitors.