Self-assembled microflower-like NiCo2X4 (X = O, S, Se) as electrodes for asymmetric supercapacitors

The substitution of chalcogen elements has a notable influence on the microstructure and electrochemical properties of transition metal oxides. However, the underlying mechanism necessitates clarification. In this investigation, self-assembled microflower-like NiCo2X4 (X = O, S, Se) structures were successfully synthesized, and their microstructures and electrochemical performance were systematically examined using both theoretical and experimental approaches. Theoretical analysis demonstrated that the replacement of chalcogen elements significantly enhances the energy band structure of the material, thus effectively improving its electrochemical performance. Experimental results revealed that, in comparison to NiCo2O4 and NiCo2S4, NiCo2Se4 displayed remarkable electrochemical performance, with a specific capacitance of 1899 F g-1 at a current density of 1 A g-1 and a promising rate capability (with a capacitance retention increase of up to 71.9% when the current density was elevated from 1 A g-1 to 10 A g-1). Additionally, the asymmetric device (NiCo2Se4//AC), composed of NiCo2Se4 as the positive electrode and activated carbon (AC) as the negative electrode, exhibited an energy density of 42.44 Wh kg-1 at a power density of 1600 W kg-1. As a result, this study offers novel insights into the fabrication of transition metal compounds for energy storage applications.