3D hierarchical core–shell spiny globe shaped Co2P@Ni2P/NiCo2O4@CoO for asymmetric supercapacitors

Abstract

Improving the electron transfer kinetics and optimizing the electrode morphology for efficient electrolyte diffusion are effective strategies for achieving high-performance asymmetric supercapacitors (ASCs). Herein, we construct a novel ZIF-67-derived 3D hierarchical core–shell spiny globe with flat leaves-shaped heterostructure (Co₂P@Ni₂P/NiCo₂O₄@CoO–NF, CNNCC–NF) with improved electron conductivity. The unique morphology is composed of Co₂P@Ni₂P/NiCo₂O₄ as a shell and CoO as a core. The conductivity of CNNCC–NF is effectively improved by the introduction of the P element. Density functional calculation results also confirm that the phase interface charge density of CNNCC–NF is high, and the E_F of CNNCC–NF crosses the CB, which results in facile charge transfer and metal-like conductivity. In addition, this morphology provides an effective space for electrolyte diffusion to achieve high electrochemical performance for ASCs. Benefitting from the synergistic effects of improved conductivity and the hierarchical pore structure, the CNNCC–NF electrode demonstrates an ultrahigh areal capacitance of 10.11 F cm⁻² at a current density of 2 mA cm⁻² (2641.15 F g⁻¹ at 0.52 A g⁻¹) in a three-electrode system. ASC devices employ CNNCC–NF as the positive electrode and activated carbon–nickel foam (AC–NF) as the negative electrode exhibiting the state-of-the-art energy density of 84.03 W h kg⁻¹ at a power density of 364.4 W kg⁻¹, as well as excellent stability with 87.30% capacitance retention after 10 000 cycles and a coulombic efficiency of more than 95% at 20 mA cm⁻² (4.40 A g⁻¹) among similar types of ASCs. The rational design and construction of 3D hierarchical core–shell spiny globe with flat leaves-shaped porous CNNCC–NF with high conductivity paves a new way to achieve high-performance ASCs.