3D hollow NiCo LDH nanocages anchored on 3D CoO sea urchin-like microspheres: A novel 3D/3D structure for hybrid supercapacitor electrodes

The research on the structure of advanced electrode materials is significant in the field of supercapacitors. Herein, for the first time, we propose a novel 3D/3D composite structure by a multi-step process, in which 3D hollow NiCo LDH nanocages are immobilized on 3D sea urchin-like CoO microspheres. Results show that the 3D CoO acts as an efficient and stable channel for ion diffusion, while the hollow NiCo LDH provides abundant redox-active sites. The calculated results based on density function theory (DFT) show that the CoO@NiCo LDH heterostructure has an enhanced density of states (DOS) near the Fermi level and strong adsorption capacity for OH-, indicating its excellent electrical conductivity and electrochemical reaction kinetics. As a result, the CoO@NiCo LDH electrode has an areal specific capacity of 4.71C cm-2 at a current density of 3 mA cm-2 (440.19C g-1 at 0.28 A g-1) and can still maintain 88.76 % of the initial capacitance after 5000 cycles. In addition, the assembled hybrid supercapacitor has an energy density of 5.59 mWh cm-3 at 39.54 mW cm-3.