Construction of Ta-Cu7S4 negative electrode for high-performance all-solid-state asymmetric supercapacitor

Abstract

Constructing electronic structure of the electrode materials is an effective approach to enhance the electrochemical activity. The substitution of high-valence metal ions can optimize the electronic structure of host materials. And there are few reports using this way to enhance supercapacitor performances. Herein, the isomorphous replacement by tantalum in Cu7S4 (Ta-Cu7S4) materials were fabricated by hard-template method and designed as negative electrode materials for solid-state supercapacitor (SSC). The unique hollow structure increased the specific areas of active materials and enabled the effective contact between electrode and electrolyte. Density functional theory (DFT) calculations indicate that the replacement of Ta element optimized the electronic structure, endowing the Ta-Cu7S4 with good electrical conductivity and more active sites. Moreover, the Ta element acted as an ‘electron reservoir’, which decreased the adsorption energy of OH– on the surface of electrode material, carried the electron to trigger redox reaction on Cu active sites continuously. These factors resulted the obtained Ta-Cu7S4 exhibited the excellent supercapacitor performances. When used as a negative electrode material, the Ta-Cu7S4 had an outstanding specific capacitance (675F g−1 at 1 A g−1) and good rate capacity (363.1F g−1 at 10 A g−1). In addition, the assembled SSC showed high energy density (111.1 Wh kg−1 at power density of 800 W kg−1) and long-term cyclic stability of retaining 83.3% after 5000 charge/discharge cycles. This work reports a low-cost and efficient Cu7S4-based supercapacitor material by Ta incorporating, and infer this new strategy can be used in other energy storage application devices.