Three-dimensional Binder-Free Electrodes with High Loading of Electroactive Material for High Performance Asymmetric Supercapacitors

Rational design of electrode material structure is a key factor to improve high energy density/power density and long lifetime of supercapacitors. Here, a simple two-step hydrothermal strategy was used to synthesize Co3O4 on nickel foam (NF), and a core-shell heterostructure was constructed by growing ZnCo bimetallic lay-ered double hydroxides (LDH) on Co3O4 scaffolds. Because of its unique heterogeneous structure and optimiza-tion of different components, the electrochemical performance of the active components was maximized because of the synergistic effect. The electrode material can achieve a high-quality loading of 13-15 mg cm-2. The binder-free electrode material Co3O4@Zn1Co2-OH grown directly on NF can achieve a high areal capaci-tance of 10.5 F cm-2 at 5 mA cm-2 and rate performance (82.9 % retention at 30 mA cm-2) and long dura-bility (62.3 % capacitance retention at 30 mA cm-2). Additionally, a Co3O4@Zn1Co2-LDH//ZiF-8 DC (ZiF-8 Derived Carbon) asymmetric supercapacitor (ASC) is assembled with an operating voltage of 1.5 V. The ASC device delivers a maximum energy density of 1.1 mWh cm-2 (33.7 Wh kg-1) at a power density of 4.0 mW cm-2 (19.6 W kg-1) and exceptional cycling stability (82.0 % of capacitance retention after 10,000 cycles at 30 mA cm-2). This work demonstrates that hierarchical core-shell heterostructures show great poten-tial in development of next-generation electrochemical energy storage devices.