Interlayer spacing-controlled carnation flower-like microstructure of nickel-manganese layered double hydroxide for enhancing hybrid supercapacitor performance

Energy harvested from intermittent sources can be stored in supercapacitors for high-power delivery with long cycling stability. Binary layered double hydroxide (LDH) materials have great potential for hybrid supercapacitor applications owing to their mixed and tunable charges and layered structure. This study presents carnation flower-like, 3D micro-structured NiMn-LDH prepared by a facile single-step hydrothermal synthesis using hexamethylenetetramine to produce hydroxides. The 3D structure was assembled from ultrathin 2D NiMn-LDH nanosheets, and the largest interlayer spacing was obtained by optimizing synthesis parameters, such as Ni:Mn molar ratio and reaction temperature, ensuring a fast diffusion and thus the best energy storage performance. The optimized NiMn-LDH electrode delivered a high specific capacity of 612 C g−1 with an excellent rate capability of 67% at 20 A g−1 in a three-electrode test. An asymmetric device assembled using NiMn-LDH and reduced graphene oxide as positive and negative electrodes provided a high energy density of 60.0 Wh kg−1 and power density of 17.7 kW kg−1 with 90.4% capacity retention after 10,000 charge–discharge cycles. This superior result highlights the potential industrial applications, such as portable electronics and trams.