Preparation And Electrochemical Properties Of LDHs With 3D Hierarchical Structure And Interconnected Mesoporous Characteristics

Layered double hydroxides have attracted extensive attention in the application of supercapacitor electrode materials due to their controllability of laminate elements and exchangeability of laminate anions.The conventional layered double hydroxide has a two-dimensional sheet structure.There are many problems such as sheet stacking,insufficient exposure of active sites,etc.,however,layered double hydroxides having a three-dimensional structure can provide more active sites for electrochemical reactions.And due to the limited conductivity of these materials,it is often necessary to add a conductive agent when making the electrode material.In this paper,from the perspective of structural design of LDHs,the preparation methods of LDHs with excellent capacitance properties for constructing three-dimensional interconnected porous structures are discussed and their electrochemical properties are explored.A TiN ultrafine powder is used as a conductive agent instead of acetylene black for the preparation of an electrode material.The main results are as follows:?1?3D flower structure Ni₄Al₁-LDH was prepared by hydrogenation method.The synthesis conditions for the three-dimensional structure Ni₄Al₁-LDH generated by hydrothermal generation were investigated:the molar ratio of Ni²⁺and Al³⁺was 4:1,120°C,12 h.Further preparing an electrode material Ni₄Al₁-LDHTiN using TiN ultrafine powder as a conductive agent.According to the electro-chemical performance test,the integral area of the CV curve of the Ni₄Al₁-LDH_TiN electrode is larger than that of the acetylene black as the conductive agent.The Ni₄Al₁-LDH_TiN electrode exhibits a specific capacitance of 290.33 F/g at a current density of 1 A/g,which is higher than the 222.77 F/g of the Ni₄Al₁-LDH_ACET electrode.The AC impedance test showed that the charge transfer resistance of the Ni₄Al₁-LDH_TiN electrode was smaller and showed better electrochemical performance.The use of TiN for electrode material preparation also provides new ideas for the development of conductive agents.?2?3D flower structure CoMnAl-LDH-A was prepared by hydrothermal method.Due to the disadvantages of binary Ni₄Al₁-LDH,such as structural instability,low capacity,and small three-dimensional holes.Aiming at this,the CoMnAl-LDH-A with3D flower-like pore structure was synthesized by using ethanol as solvent and 140°C for 12 h.SEM showed that the ternary CoMnAl-LDH-A formed a more stable three-dimensional flower-like structure.It was found by electrochemical performance test that the specific capacity of ethanol solvent hydrothermal method reached 662 F/g,which was much higher than that of 143 F/g synthesized with water solvent,and at a high current density of 10 A/g,the specific capacitance is still higher than that of the water solvent synthesis sample.?3?Hydration of hydrazine hydrate to prepare three-dimensional interconnected porous structure 3D-NiCo-SDBS-LDH.The structure was characterized by SEM,HRTEM,XRD,FTIR,BET,UV-vis,and its electrochemical performance was explored.SEM shows that the prepared 3D-NiCo-SDBS-LDH forms a 3D interconnected porous structure.The interplanar spacing of XRD?012?is expanded from 0.25 nm of the first synthetic NiCo-SDBS-LDH to 0.27 nm.The specific surface area increased from 41.52m²/g to 55.68 m²/g.UV-visible spectroscopy shows that the electronic transition energy can be reduced from 2.52 to 2.19,making electrons easier to transition in electrochemical reactions.The three-electrode test showed a specific capacitance of1147.7 F/g at 1 A/g current density,which is much higher than the 789 F/g of the pre-modification sample.The assembled asymmetric supercapacitor 3D-NiCo-SDBS-LDH//AC device maintains 96%excellent cycle stability after 10,000 cycles at a current density of 5 A/g,which is much higher than the 84.7%of the original sample.