Sandwich-like high-performance Ti3C2Tx MXene/NiCo2O4 nanosphere composites for asymmetric supercapacitor application

NiCo2O4 is a promising electrode material for supercapacitors due to its low cost, high theoretical specific capacitance and good cycling stability. However, NiCo2O4 has the disadvantages of poor electronic and ionic conductivities and easy agglomeration. Moreover, the irreversible structural damage caused by the NiCo2O4 volume expansions during charging and discharging limits its use in supercapacitors. Herein, we fabricated sandwich Ti3C2Tx MXene/NiCo2O4 composites via an electrostatic self-assembly method. The problem of easy agglomeration of the NiCo2O4 nanospheres was solved by intercalating Ti3C2Tx MXene layers with the NiCo2O4 nanospheres. Furthermore, the Ti3C2Tx MXene layer was also utilized as a protective layer to limit serious volume expansion and protect the structure of NiCo2O4 nanospheres from destruction. The results showed that the prepared Ti3C2Tx MXene/NiCo2O4 composite exhibited a high specific capacitance of 1025 F g−1 at a current density of 1 A g−1 and had an initial capacity of 81 % when the current density was increased to 10 A g−1. The Ti3C2Tx MXene/NiCo2O4 composite cathode and activated carbon anode were assembled in an asymmetric supercapacitor, which showed an energy density of 36.67 Wh kg−1 at 800 W kg−1 and a capacity retention of 88.2 % after 5000 cycles.