Asymmetric, Flexible Supercapacitor Based on Fe-Co Alloy@Sulfide with High Energy and Power Density.

Electrode materials with high conductivities that are compatible with flexible substrates are important for preparing high-capacitance electrode materials and improving the energy density of flexible supercapacitors. Here, we report the design and fabrication of a new type of flexible electrode based on nanosheet architectures of a Co-Fe alloy (FeCo-A) coated with ternary metal sulfide composites (FeCo-Ss) on silver-sputtered carbon cloth. The high conductivity of the flexible substrate and the iron-cobalt alloy skeleton enables good electron transmission through the material. In particular, the outer FeCo-S layer has an average thickness of ∼30 nm, providing many active sites. This layer also inhibits the oxidation of the alloy. The electrode material is close to 20 nm thick, which limits inaccessible volumes and promotes high utilization of FeCo-alloy@FeCo-sulfide (FeCo-A-S). The additive-free FeCo-A-S electrode has a high specific capacitance of 2932.2 F g at 1.0 A g and a superior rate capability. All-solid-state supercapacitors based on these electrodes have a high power density of 8000 W kg and a high energy density of 46.1 W h kg.