MXene-wrapped ZnCo2S4 core-shell nanospheres via electrostatic self-assembly as positive electrode materials for asymmetric supercapacitors

Constructing electrode materials with large capacity and good conductivity is an effective approach to improve the capacitor performance of asymmetric supercapacitors (ASCs). In this paper, ZnCo2S4 core-shell nanospheres are constructed by two-step hydrothermal method. In order to improve the chemical activity of ZnCo2S4, ZnCo2S4 is activated using cetyltrimethylammonium bromide (CTAB). Then, MXene nanosheets are fixed on the surface of ZnCo2S4 by electrostatic self-assembly method to improve the specific surface area of ZnCo2S4 and MXene-wrapped ZnCo2S4 composite is prepared in this work. Owing to the synergy effect between MXene nanosheets and ZnCo2S4 core-shell nanospheres, the as-prepared composite displays fast ion transfer rate and charge/discharge process. The capacity of the MXene-wrapped ZnCo2S4 composite can reach 1072 F.g(-1), which is far larger than that of ZnCo2S4 (407 F.g(-1)) at 1 A.g(-1). An ASC device is assembled, which delivers 1.7 V potential window and superior cyclic stability (95.41% capacitance retention). Furthermore, energy density of this device is up to 30.46 Wh.kg(-1) at a power density of 850 W.kg(-1). The above results demonstrate that MXene-wrapped ZnCo2S4 composite has great application prospects in electrochemical energy storage field.