The rational design of hierarchical CoS2/CuCo2S4 for three-dimensional all-solid-state hybrid supercapacitors with high energy density, rate efficiency, and operational stability

In the context of developing all-solid-state hybrid supercapacitor devices with superior performance, and excellent charge storage, energy and power densities, working stability, and rate efficiency, herein, we have adopted an anion-exchange method to design hierarchically structured CoS2/CuCo2S4 with multiple reactive equivalents, enhanced conductivity, and a distinctive ion-permeable bulk microstructure. The electrochemical investigation of CoS2/CuCo2S4 in a three-electrode setup revealed the excellent high-rate specific capacitance (1492 F g−1 at 6 A g−1), strong redox reversibility, trivial voltage drop, extremely low charge transfer (approximately 0.23 Ω), and low Warburg and equivalent series (0.78 Ω) resistance of the material. Furthermore, a thorough electrochemical study of the CoS2/CuCo2S4‖N-rGO all-solid-state hybrid supercapacitor (ASSHSC) device (with CoS2/CuCo2S4 and N-rGO as the positive and negative electrode materials, respectively) showed a substantial faradaic contribution to the overall charge storage, a small high-rate overpotential, an insignificant voltage drop, exceptional rate capacitance/capacity, excellent coulombic efficiency under high-rate conditions, and very low charge transfer and equivalent series resistance. The CoS2/CuCo2S4‖N-rGO ASSHSC device offers remarkable high-rate energy density (20.7 W h kg−1 at an extreme power density of approximately 23 000 W kg−1) and operational stability (approximately 92.8% after 10 000 GCD cycles). The excellent energy storage performance of the CoS2/CuCo2S4-based ASSHSC device is ascribed to the abundant boundary pores and inter-crystallite pores, multiple redox possibilities (due to Co3+, Co2+, and Cu2+), electroactive ion-reservoir-like behaviour, active CoS2|CuCo2S4 interface, enhanced electromechanical stability of the electrode materials, and CoS2- and N-induced improved conductivity of CoS2/CuCo2S4 and N-rGO, respectively.