Rational design of flower-like FeCo2S4/reduced graphene oxide films: Novel binder-free electrodes with ultra-high conductivity flexible substrate for high-performance all-solid-state pseudocapacitor

With the aim of developing sustainable energy storage and a flexible device exhibiting excellent electrochemical performance, a supercapacitor system comprising a highly reduced graphene oxide film (RGOF) as substrate and a spinel flower-like FeCo2S4 array as the active material is fabricated. The specific capacitance of the FeCo2S4/RGOF electrode reaches 2487.97 F g−1 at a current density of 5 mA cm−2 while maintaining superior stability with 95.9% capacitance retention after 5000 cycles, thereby surpassing that of previously reported Fe-Co bimetallic sulfides. This is ascribed to the synergistic effect between conductive RGOF and active FeCO2S4, which are rich in redox reactions. The fabricated FeCo2S4/RGOF is utilized as a positive electrode in an asymmetric supercapacitor, delivering a high energy density of 88.2 W h kg−1 at 800 W kg−1. Furthermore, the supercapacitor exhibits excellent cycling stability with 85.1% capacitance retention after 5000 cycles at 5 A g−1 and outstanding persistence after different deformation conditions. Thus, the FeCo2S4 hybrid film electrode with specific flexibility shows potential applicability in portable and wearable energy storage devices.