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

Abstract

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 (rGO_sp) 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-rGO_sp) provides a specific capacitance (C_S) of 98 F g⁻¹ (at 4.5 A g⁻¹), coulombic efficiency of ∼99% at 15 A g⁻¹, and C_S 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-rGO_sp 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.