High-performance positive electrode material of MXene/FeNi₂S₄ nanocomposite for flexible supercapacitor with large potential window

Developing heterostructured nanomaterials with abundant active sites and excellent electronic conductivity is essential to enhance the electrochemical activity of supercapacitors. Herein, MXene/FeNi₂S₄ composites, as a high-performance electrode material for the flexible supercapacitor, were fabricated using a simple probe sonication method. The formation of a 3D architecture can create abundant electrochemical active sites, promoting the charge transfer as well as the redox reactions. Accordingly, a supercapacitor electrode based on MXene/FeNi₂S₄ exhibited excellent electrochemical performances, with a high specific capacitance of 673 F/g at 1 A/g. When MXene/FeNi₂S₄ was used as the electrode material of an asymmetric supercapacitor, the device showed an outstanding specific capacitance of 141 F/g at 1 A/g in a large potential window of 1.8 V. Up to 90 % of this high specific capacitance was retained after 2000 charge–discharge cycles. Furthermore, the device displayed high values of both energy density (63.37 Wh/kg) and power density (900.98 W/kg). The device also exhibited stable electrochemical performances under high flex at the bending angle of 135°. The exceptional electrochemical performances of MXene/FeNi₂S₄ highlight its great potential as an excellent electrode material for the next generation of flexible energy storage devices.