Preparation And Performance Of Doped LDH Supercapacitor Electrode Materials By Electrodeposition

Layered double hydroxides（LDHs）,have become one of the candidate materials for supercapacitor,due to their high theoretical capacity,tunable chemical composition,high redox activity,and outstanding anion-exchange capability.Nevertheless,the poor electrical conductivity and short cycle life limit the practical application of this pseudocapacitive material.To solve this problem,the researchers improved the electrochemical properties of the materials by synthesizing LDH-based composites with special structure and anion insertion.LDH can be prepared by hydrothermal,electrodeposition,co-precipitation,and ion exchange,etc.Electrodeposition method has the advantages of short preparation time,high controllability,and low cost.Therefore,we used the electrodeposition method to prepare LDH-based composites and anion-doped LDH materials,characterized them,and investigated the electrochemical properties of the materials.A hierarchical Co Mn-LDH@Ni（OH）₂composites grown on nickel foam are prepared via a facile two-step electrodeposition process.The doping of Mn elements improves the electrochemical properties of Co（OH）₂.Because of the high specific surface area of the composite material and the synergistic effect of the two-component materials,the Co Mn-LDH@Ni（OH）₂exhibits excellent specific capacitance and superior rate capability.At a current density of 1 A·g^-1,the specific capacitance is as high as 2795.6F·g^-1;when the current density is increased to 20 A·g^-1,the specific capacitance is still2589.1 F·g^-1（92.6%capacitance retention）.This electrode was assembled with an activated carbon（AC）electrode as an asymmetric supercapacitor（ASC）with an energy density of 31.5 W·h·kg^-1at a power density of 400 W·kg^-1.Sulfur-doped NiCo-LDH（NiCo-SOH）nanosheet arrays were prepared on the surface of nickel foam by one-step electrodeposition.the introduction of S ions not only improved the electrical conductivity of the material but also provided a richer redox pair reaction,which effectively improved the electrochemical properties of the material.the sample with a Ni/Co ratio of 1:1 has a large specific surface area,which is conducive to the electrode material to expose more active sites,and the cross-linked nanosheet structure shortens the electron transfer and electrolyte diffusion paths,which helps to improve the material performance and has a specific capacitance of up to2161.27 F·g^-1at 1 A·g^-1.This NiCo-SOH electrode was assembled as the ASC with an energy density of 34.3 W·h·kg^-1at a power density of 400 W·kg^-1,as well as excellent cycling stability performance(98%capacitance retention over 9000 cycles at 2 A·g^-1).The deposition process is an important factor affecting the microscopic morphology of NiCo-SOH materials.The samples prepared at smaller currents,voltages,and times have larger specific surface areas and three-dimensional cross-linked nanosheet structures,which facilitate the exposure of active sites in the electrolyte and accelerate the charge transfer and ion diffusion rates.The sample deposited at 4 V for 1 min with a Ni/Co ratio of 1:1 was found to have a better morphology,which is favorable for the material properties.The specific capacitance is as high as 3079.1 F·g^-1at a current density of 1 A·g^-1.