“Ship in a Bottle” design of ZIF-9@CoAl LDH hybrid compound as a high performance asymmetric supercapacitor

Abstract

Constructing a particular nanostructure and improving electrical conductivity are two effective ways to improve the charge storage of LDH-based electrode materials. An asymmetric supercapacitor coupled with double-layer capacitance materials is the most promising strategy to improve the performance of a supercapacitor device. In this study, the ZIF-9@CoAl LDH compound was successfully synthesized by a “Ship in a Bottle” method. The conductivity of CoAl LDHs was improved by the introduction of 2D ZIF-9 micro-slices. The ZIF-9@CoAl LDH hybrid structure exhibited a high specific capacitance of 702.7 F g⁻¹ at 1 A g⁻¹ compared with that of the pure CoAl LDHs of 518.7 F g⁻¹ at 1 A g⁻¹ and recorded a favorable rate capability of 73.8% when the current density is up to 20 A g⁻¹ (56.1% of pure CoAl LDHs). Besides, the assembled ZIF-9@CoAl LDHs//activated carbon asymmetric supercapacitor cell device worked synergistically to achieve a high energy density of 32.1 W h kg⁻¹ with a power density of 1000 W kg⁻¹ and a capacity retention of 75% after 5000 cycles. This work provides a simple strategy to improve the rate capability and energy storage performance of LDH-based materials.