ZIF-67 derived high stability CoNi2S4/carbon/MXene composites as an enhanced electrode for asymmetric supercapacitor

Supercapacitors have received widespread attention from scientific researchers due to the advantages of high power density, fast charging/discharging rate and long cycle life. Among them, the development of high performance and high safety electrode materials are important research topics in the field of supercapacitors. Herein, zeolitic imidazolate framework (ZIF) derivatives is a good candidate material for supercapacitors electrode because of its controllable pore rate, constant cavity and larger specific area. However, the reunion phenomenon and the damaged structure during the reaction seriously affected its electrochemical properties, especially its stability. To solve this problem, the few-layer MXene was added into ZIF-67 to inhibit the reunion of single materials and the carbonization process was operated to improve its conductivity and structure stability. In addition, the CoNi2S4/carbon/MXene (CNS/C/MXene) obtained by the solvent thermal method successfully inherited the hollow cages structure and rough surface from the precursor, expressing a better electrochemical performance. In three-electrode system, the CNS/C/MXene electrode can exhibit the specific capacitance of 1221.6 F g-1 (169.7 mAh g-1) at 1 A g-1 and still maintain a high capacitance of 966.4 F g-1 (134.2 mAh g-1) at 20 A g- 1 (79.1 % of the former). After assembling it with activated carbon into asymmetric supercapacitor, the device can provide a high energy density of 19.82 Wh kg-1 at a power density of 469.31 W kg-1 and maintain about 71.17 % of the initial capacitance after 30,000 cycles under a current density of 20 A g-1, representing excellent cycle stability and rate capability.