Three-dimensional binder-free electrodes with high loading of electroactive material for high performance asymmetric supercapacitors

Abstract

ZnCo bimetallic LDH is successfully grown on 3D Co 3 O 4 scaffolds on nickel foam as a stable hierarchical core-shell heterostructural electrode. Benefiting from the fine ion/electron transport within Co 3 O 4 @Zn 1 Co 2 -LDH electrode, the prepared Co 3 O 4 @Zn 1 Co 2 -LDH//ZiF-8 DC asymmetric supercapacitor exhibits a high energy density of 1.1 mWh cm -2 at a power density of 4.0 mW cm -2 , which is superior to the values of previous reports. • Three-dimensional binder-free electrodes are constructed with a core-shell heterostructure. • The electrode material can achieve a high quality loading of 13∼15 mg cm -2 . • The electrode achieves high areal capacitance of 10.5 F cm -2 at 5 mA cm -2 and high long durability. • The ASC device delivers a high energy density of 1.1 mWh cm -2 at a power density of 4.0 mW cm -2 . • The ASC device shows 82.0% of capacitance retention after 10000 cycles at 30 mA cm -2 . 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 Co 3 O 4 on nickel foam (NF), and a core-shell heterostructure was constructed by growing ZnCo bimetallic layered double hydroxides (LDH) on Co 3 O 4 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 Co 3 O 4 @Zn 1 Co 2 -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 Co 3 O 4 @Zn 1 Co 2 -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 10000 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.