Flexible Solid-State Asymmetric Supercapacitor with High Energy Density and Ultralong Lifetime Based on Hierarchical 3D Electrode Design

Hierarchical structure design of transition metal compounds is a promising method for improving the electrochemical properties of supercapacitors. In this work, a 3D electrode is obtained by in situ growing of NiMoO4@NiCo2O4 core–shell nanorods on Ni foam (NF) followed by an annealing process (NF@NiMoO4@NiCo2O4). The hierarchical structure with ordered pores on a surface enables a uniform charge distribution, provides effective electron/ion transfer channels, and maintains structural integrity over long periods of cycling, which collectively results in excellent electrochemical properties with an extraordinary specific capacitance of 1920 F g–1 at 1 A g–1 as well as 91.6% capacitance retention after 10 000 cycles. Furthermore, a flexible solid-state asymmetric supercapacitor fabricated with NF@NiMoO4@NiCo2O4 achieves a superior energy density of 54.5 Wh kg–1 (at 845 W kg–1) and an outstanding cycling stability with 83% capacity retention over 10 000 cycles. The hierarchical 3D electrode design in this work will contribute to the development of high-performance supercapacitors and shows promising prospects in flexible and portable energy storage systems.