Entire synergistic contribution of electrodeposited battery-type NiCo₂O₄@Ni_4.5Co_4.5S₈ composite for high-performance supercapacitors

A series of novel hierarchical NiCo₂O₄@Ni_4.5Co_4.5S₈ composites grown on nickel foam are synthesized via a two-step electrodepositon process with a post-annealing procedure. The firstly-grown vertical NiCo₂O₄ nanosheet arrays serve as skeleton for the subsequent growth of horizontally Ni_4.5Co_4.5S₈ nanosheets, generating abundant active sites for speedy redox reactions. As a supercapacitor material, NiCo₂O₄@Ni_4.5Co_4.5S₈-4 demonstrates a high specific discharge capacity of 369 mA h g⁻¹ at 1 A g⁻¹, a superior rate capability of displaying 258 mA h g⁻¹ at 20 A g⁻¹ and an ideal cycling stability of merely 4.8% capacity loss after 5,000 cycles. The kinetic analysis is performed to qualitatively confirm the charge storage mechanism, manifesting that capacitive effect is dominant in the total capacity. In addition, the assembled NiCo₂O₄@Ni_4.5Co_4.5S₈-4//activated carbon aqueous hybrid supercapacitor device exhibits a superior specific energy (124.77 Wh kg⁻¹ at 1.08 kW kg⁻¹) and specific power (39.29 Wh kg⁻¹ at 15.21 kW kg⁻¹). The self-discharge analysis reveals that it takes more than 26 h for the voltage to drop to 0.75 V. 83.56% of initial capacity is maintained after 5,000 cycles at 100 mV s⁻¹, verifying the satisfactory stability. Therefore, the outstanding electrochemical property enables NiCo₂O₄@Ni_4.5Co_4.5S₈-4 composite to become a potential electrode material for practical applications.