Heterostructured bimetallic-sulfide@layered Ti3C2Tx-MXene as a synergistic electrode to realize high-energy-density aqueous hybrid-supercapacitor

Aqueous hybrid supercapacitors (AHSCs) exhibit promising electrochemical performance with long cyclic stability and high power density. However, the low-energy density restricted their development to commercialization. To improve the energy density, we proposed a heterostructured (HS) composite of nickel-cobalt-sulfide (NCS) nanoflowers embedded in exfoliated Ti3C2Tx-MXene layers (HS-NCS@MXene). The NCS nanoflowers were uniformly dispersed inside the MXene layers and formed a sandwich-like structure. The HS-NCS@MXene exhibited remarkable pseudocapacitive performance in a three-electrode system. The capacitance can reach 2637 F g(-1) (1582 C g(-1)) at 2.5 A g(-1) with stable cycling life over 10,000 cycles and retained 96% capacity of the initial value. Post-mortem investigations confirmed that the charge storage mechanism in HS-NCS@MXene composite is a combination of Faradic and electrochemical double-layer storage. An AHSC was assembled by coupling the HS-NCS@MXene as a positive electrode and activated carbon as a negative electrode (HS-NCS@MXene//AC-AHSC). The HS-NCS@MXene//AC-AHSC can operate in a potential range up to 1.6 V and deliver a high capacitance of 226 F g(-1) at 1.5 A g(-1) with stable cyclic life (92%) up to 20,000 cycles. Moreover, the HS-NCS@MXene//AC-AHSC also possessed a high energy density of 80 Wh kg(-1) at a power density of 1196 W kg(-1), which exceeds most recently published works. The synergistic effect of NCS and MXene enables the HS-NCS@MXene composite to deliver outstanding electrochemical performance for AHSCs.

Automated summary

In this study, a heterostructured composite of nickel-cobalt-sulfide nanoflowers embedded in exfoliated Ti3C2Tx-MXene layers was proposed to enhance the energy density and electrochemical performance of aqueous hybrid supercapacitors (AHSCs). The composite exhibited remarkable pseudocapacitive performance and could operate in a wide potential range with high capacitance and stable cyclic life. The synergistic effect of NCS and MXene enabled the composite to deliver outstanding electrochemical performance for AHSCs.