Nanostructured Mn-Doped Ni–Co Hydroxide Microspheres for Fast-Kinetics Supercapacitors

Transition-metal double hydroxides offer many benefits, including abundant nanostructures, low cost, easy preparation, diverse compositions, and adjustable physicochemical properties, which have a wide range of applications and are highly promising for the development of high-performance electrode materials. Herein, hydrangea-like manganese-doped nickel–cobalt double hydroxide (NiCoDH-Mn) nanostructures were prepared through a fast one-step microwave hydrothermal method within a few minutes. A thorough analysis was conducted on how the nanostructure, crystal structure, and electrochemical properties of the samples were affected by the amount of the Mn doping content. Density functional theory (DFT) calculations demonstrated that the introduction of Mn doping can generate impurity levels around the Fermi level of NiCoDH, enhancing its electrical conductivity. At a current density of 1 A g^–1, the optimized NiCoDH-Mn has a remarkable specific capacity of 107.4 mA h g^–1. Even when the current density increases by 15 times, it can still maintain a high specific capacity of 66.3 mA h g^–1. After undergoing 1500 cycles with a current density of 5 A g^–1, the electrode’s capacity remains 128%. The hybrid supercapacitor consisting of the NiCoDH-Mn cathode and mango seed-derived activated carbon anode has an impressive energy density of 47.9 W h kg^–1 and a power density of 850 W kg^–1. Moreover, it boasts an impressive capacitance retention rate of 87.5%, even after 5000 cycles. We offer a highly effective and speedy approach to creating high-performance transition-metal hydroxides that are ideal for energy storage systems.