High-performance flexible solid-state asymmetric supercapacitor with NiCo2S4 as a cathode and a MXene-reduced graphene oxide sponge as an anode

Ti3C2 MXenes have revealed immense potential in energy storage systems. Herein, we report the development of a flexible solid-state asymmetric supercapacitor (ASC) device by assembling spherical NiCo2S4 as a cathode, a MXene-reduced graphene oxide sponge (rGOsp) nanocomposite as an anode, and polyvinyl alcohol (PVA) hydrogel comprising a mixture of 3 M KOH and 0.1 M K4[Fe(CN)6] as an electrolyte cum separating membrane. This device (NiCo2S4//MXene-rGOsp) provides a specific capacitance (CS) of 98 F g−1 (at 4.5 A g−1), coulombic efficiency of ∼99% at 15 A g−1, and CS of ∼95% after 4000 cycles. Moreover, it provides an energy density of 35.75 W h kg−1 at a power density of 3693 W kg−1. This device establishes its mechanical flexibility by exhibiting almost similar performances at various deformed structures. The performance of this flexible NiCo2S4//MXene-rGOsp ASC device is superior to many reported MXene-based supercapacitors. This device is also capable of illuminating a series of LED lights. In conclusion, the results clearly prove the potential of this device in high-performance energy storage applications.