Spherical CuFeS2@FeSe2 structure as a binder-free electrode and its performance in asymmetric supercapacitors

Abstract

Transition metal chalcogenides (TMCs), such as FeSe₂, FeS₂, and CuS, have attracted considerable attention for energy storage due to their multi-electron transfer capabilities and high capacities. This study presents the synthesis of spherical CuFeS₂ through a binder-free hydrothermal process, incorporating selenium powder to form hollow spheres of CuFeS₂ encapsulated by FeSe₂ nano-planes (CuFeS₂@FeSe₂). Utilizing a modified electrode without a binder and adopting a spherical CuFeS₂@FeSe₂ structure significantly enhance the performance of asymmetric supercapacitors. The absence of a binder eliminates potential issues associated with binding agents, ensuring a more efficient charge transfer. The spherical configuration, with FeSe₂ layers surrounding and encapsulating the CuFeS₂ core, contributes to improved capacitance and stability. The unique structure allows for better utilization of active materials, enhancing the specific capacitance of the electrode. This modified electrode demonstrates remarkable cyclic stability, indicating its potential for long-term practical applications. This unique nanostructure was characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), demonstrating enhanced nanomaterial conductivity. Electrochemical performance analyses, including cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS), reveal a specific capacity of 1306 A g⁻¹ at a current density of 2 A g⁻¹ in a three-electrode system. Furthermore, as a positive electrode in an asymmetric supercapacitor device (CuFeS₂@FeSe₂||AC), paired with activated carbon@NF (AC) as a negative electrode, the system achieves an efficient energy density of 152.01 W h kg⁻¹ with superior durability, retaining 91.03% capacity after 3000 cycles.