General strategy toward hexagonal ring-like layered double hydroxides and their application for asymmetric supercapacitors.

• A universal approach for the preparation of hexagonal ring-like LDH was proposed. • A series of hexagonal ring-like LDH were synthesized by a universal NaOA-assisted TTS method. • The formation mechanism of nanoring was systematically studied. • As-prepared ring-like CoAlNi LDH exhibited enhanced supercapacitor performance than that of the plate-like LDHs. Hexagonal ring-like structure of ternary-component layered double hydroxide (LDH) could be promising materials for advanced energy storage and conversion systems. However, it is still a great challenge to present a universal and cost-effective approach to fabricate ternary-component LDH nanomaterials with ring-like micro-/nano-structure. In this work, a universal sodium oleate (NaOA)-assisted two-step two-phase solvothermal (TTS) method is developed to synthesize hexagonal ring-like structure of ternary-component LDH nanomaterials. This strategy is generic for synthesis of ring-like LDHs with different element components, such as CoAlNi, MgAlNi, and MgAlCo. The formation mechanism of nanorings constructed by TTS method is further systematically studied, which can be ascribed to the dissolution-recrystallization process driven by the solubility product of different reactant and Ostwald ripening effect. The ring-like CoAlNi LDH exhibited enhanced supercapacitor performance with a specific capacitance of 1339.6 F g−1 at 1 A g−1. Its asymmetric supercapacitor device exhibited high energy density (50.3 Wh kg−1 at a power density of 800 W kg−1) and stable cycling performance (about 82.2% capacitance retention over 3000 cycles). All of the electrochemical results of ring-like CoAlNi LDH are superior to that of pristine CoAlNi LDH nanosheets. The present work makes a significant contribution to the design and synthesis of ternary-component LDH with a unique hexagonal ring-like nano-architecture, as well as their potential applications in electrochemical energy storage. [ABSTRACT FROM AUTHOR]