Mesoporous carbon-supported flower-like Mn-doped Ni–Co layered double hydroxides with high cycling capacitance retention for supercapacitors

Abstract

Since the energy density and voltage window of supercapacitors cannot match that of lithium-ion batteries, supercapacitors are far from replacing batteries but can only be seen as a supplement to battery charge storage or transmission devices. The design of transition metal oxide-based electrodes with high cycling capacitance retention is very important for the development of supercapacitors. In this study, flower-like SAC@NiCoMn-LDH electrode materials with different Mn doping ratios were prepared by a hydrothermal method with mesoporous carbon (SAC) as the substrate. Density functional theory (DFT) calculations confirm that Mn doping can enhance the adsorption of OH⁻ and the desorption of the H proton. In addition, Mn doping increases the density of states of LDH near the Fermi level and increases the number of active electrons, which is conducive to the occurrence of electrochemical reactions. In the three-electrode system, SAC@Ni₂Co_0.95Mn_0.05-LDH with optimal doping ratio increased the specific capacitance by three times compared to that of NiCo-LDH and displayed an excellent cycling stability (83.76% capacitance retention after 50 000 cycles). Moreover, the prepared SAC@Ni₂Co_0.95Mn_0.05-LDH and commercial activated carbon (AC) were made into electrode plates and then assembled into a SAC@Ni₂Co_0.95Mn_0.05-LDH//AC asymmetric supercapacitor (ASC). The ASC exhibited high energy density (23.68 W h kg⁻¹ at 325 W kg⁻¹) and excellent specific capacitance retention (85.32% after 50 000 cycles), making it well suited for efficient wind energy storage and conversion with promising practical applications.