Three-dimensional independent CoZnAl-LDH nanosheets via asymmetric etching of Zn/Al dual ions for high-performance supercapacitors

Abstract

The design and synthesis of LDH materials with high conductivity and more exposed active sites are the current hotspots in supercapacitor energy storage. However, the practical specific capacity of LDHs is still far below their theoretical value, due to their intrinsic insulation nature, irreversible face-to-face stacking and limited exposed active surface area. Here, it is first proposed to utilize the feature of LDH morphological changes induced by Zn2+ doping, which achieves the transformation of 2D close-packed CoAl-LDH nanosheets into 3D independent loose-packed CoZnAl-LDH nanosheets. Furthermore, the surface electronic environment of Co is changed greatly and certain concentration of oxygen defects is generated of CoZnAl-LDH by partial dissolution of Zn/Al dual ions of LDH laminates in alkaline solution. These will improve the properties in both electrons conduction and ions diffusion of CoZnAl-LDH nanosheets, and thus improve the specific capacity, rate capacities and cycle stability of CoZnAl-LDH nanosheets. Compared with the non-etching CoZnAl-LDH (491 F g−1 at 1 A g−1, 76.9% capacitance retention after 4000 cycles), the obtained E-CoZnAl-LDH-8 h delivered a higher specific capacitance (946 F g−1 at 1 A g−1) and excellent long cycle life (92.3% capacitance retention after 4000 cycles). Moreover, the assembled E-CoZnAl-LDH-8 h//active carbon asymmetric supercapacitors device also showed a remarkable energy density (36.75 Wh kg−1 at 400 W kg−1) and long-term stability (72.7% capacitance retention after 8000 cycles). The “doping” and “dual ion etching” strategies proposed in this work provide theoretical guidance and experimental basis for the development of high-performance supercapacitors.