Flower-like NiMn LDH Microstructures as a Promising Cathode for High-Performance Hybrid Supercapacitors with Exceptional Energy Density.

The practical application potential of supercapacitors can be enhanced through designing high-performance electrode materials. In this work, NiMn layered double hydroxides (NiMn LDHs) were prepared through a hydrothermal method using hexamethylenetetramine (HMTA) as an alkaline source. The morphology of NiMn LDHs was regulated by controlling the amount of HMTA, and two kinds of flower-like NiMn LDH microstructures with large open voids (NiMn LDH-6) and dense smaller petals (NiMn LDH-10) were respectively synthesized using 6 and 10 mmol HMTA. When employed as electrode material in electrochemical energy storage, such three-dimensional structure helps to increase the surface area and expose more active sites, thereby promoting efficient electrolyte access and ion transport. These NiMn LDHs exhibited battery-type electrochemical behavior, and NiMn LDH-6 delivered the highest specific capacity of 795.3 C g-1, exceeding NiMn LDH-10 with 672.6 C g-1. Furthermore, LDH and activated carbon (AC) were employed as the cathode and anode, respectively, to assemble the hybrid supercapacitor (HSC) device. At 964.55 W kg-1, the NiMn LDH-6//AC delivered an exceptional specific energy of 60.94 W h kg-1, and even at higher power density of 8653.42 W kg-1, it remained 38.24 W h kg-1. Under a current load of 10 A g-1, both HSCs showed a slight capacity decay over 3,000 cycles. These findings indicate that the flower-like NiMn LDHs prepared through the current hydrothermal strategy possess promising potential in high-performance supercapacitor applications.