Tunable construction of FexCo3-xSe4 nanostructures as advanced electrode for boosting capacity and energy density

Abstract Hierarchical nanoarchitectures with large void space, unique porous networks, and numerous active sites for advanced supercapacitor (SC) electrodes has attracted great attention in modern electronics. Herein, a novel strategy is established to rational design of hierarchical iron cobalt selenide (FexCo3-xSe4) with tunable nanostructure and morphology by adjusting the stoichiometric ration of Fe: Co in order to enhance the energy density of SCs. The optimal FeCo2Se4 nanosheet arrays (NAs) enhances the electrical conductivity, electroactive sites, and intrinsic reactivity, achieving an ultra-high specific capacity of ~398.5 mA h g−1 at a current density of 1 mA cm−2 with an exceptional rate capability (~304.2 mA h g−1 at a current density of 50 mA cm−2), and ultra-long cycle life (~98.2% retention after 10,000 cycles). Taking advantage of FeCo2Se4 NAs positive electrode, we have successfully assembled solid-state asymmetric SC (ASC) with Fe2O3@NG hydrogel as the negative electrode. Impressively, the solid-state ASC achieves high operating voltage window upto 1.6 V, and thus delivers ultrahigh energy density of ~84.1 Wh kg−1 at a power density of 0.69 kW kg−1, and exceptional cycling stability (5.5% of capacity decay after 10,000 cycles), which outperform the recently reported metal selenide-based ASCs. These consequences clearly designate FeCo2Se4 NAs as an advanced electrode for next-generation energy storage technologies.