Solvothermal synthesis of cobalt nickel layered double hydroxides with a three-dimensional nano-petal structure for high-performance supercapacitors

Cobalt nickel layered double hydroxides (CoNi LDHs) have been paid much attention as electrode materials for supercapacitors. However, poor cycling stability and rate capability resulting from easy agglomeration and low electrical conductivity limited their practical applications. In this study, CoNi LDHs with a three-dimensional nano-petal structure were successfully prepared by a simple one-pot solvothermal method. During preparation, 2-methylimidazole (2-MIM) was used as a weak alkali agent and acetate anions as intercalating ions of the product to balance the charges, which ensure the formation of a unique petal structure with a cross-linked active network. This special structure provided a large number of active centers, enough space and a reaction interface, which promote rapid electrolyte ion diffusion and electron transport. Therefore, CoNi LDH-6 displayed a high specific capacity of 941.6 C g−1 at 1 A g−1, which is equal to an extremely high areal capacity of 4.61 C cm−2 at 4.9 mA cm−2. When the current density was increased to 10 A g−1, it also achieved a significant rate performance of 787 C g−1 (i.e., 3.86 C cm−2 at 49 mA cm−2). In addition, an asymmetric supercapacitor (ASC) device assembled with as-prepared CoNi LDH-6 as the positive electrode and a homemade carbon material as the negative electrode possessed a remarkable energy density of 51.1 W h kg−1 at a power density of 1.7 kW kg−1. The facile preparation and attractive performance make CoNi LDH-6 a promising candidate for high-performance supercapacitors.