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 layered double hydroxides (LDH) on Co3O4 scaffolds. Because of its unique heterogeneous structure and optimization 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 capacitance of 10.5 F cm−2 at 5 mA cm−2 and rate performance (82.9 % retention at 30 mA cm−2) and long durability (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 potential in development of next-generation electrochemical energy storage devices.