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

Abstract

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.