Three-dimensional FeNiP decorated graphene sponge: A novel flexible electrode for high-performance asymmetric supercapacitor

•Fabrication of a novel flexible FeNiP and graphene-based sponge material (3D FeNiP/GrS).•Characterization of FeNiP/GrS with various techniques.•The flexible FeNiP/GrS//GrS ASC devices.•The FeNiP/GrS is a promising candidate for producing high-energy-density electrode materials in supercapacitors. Here, a three-dimensional (3D) flexible material was prepared based on FeNiP decorated graphene sponge (GrS) by a two-step method. Free-standing 3D GrS was fabricated through a simple foaming-drying method, then FeNiP was electrodeposited onto flexible GrS material to achieve a flexible FeNiP/GrS sponge electrode for high-performance electrochemical supercapacitors. This composite material exhibited a high specific capacitance of 2292 F/g and 90% of the specific capacitance was retained after 10,000 charge/discharge cycles at a current density of 1 A/g. An asymmetric supercapacitor (FeNiP/GrS//GrS) was fabricated and this flexible circuit delivered a maximum power density of 6545 W/kg and a high energy density of 330 Wh/kg. This outstanding electrochemical performance could be attributed to the high charge conductivity of FeNiP and porous graphene sponge which provides good structure stability, large reaction surface area, and high electron transfer. [Display omitted]