Structure Regulation And Modification By High-Gravity Exfoliation For Nickel-Cobalt Layered Hydroxide Electrode Materials

In this paper,nickel-cobalt layered double hydroxides（Ni-Co LDHs）have been prepared by solvothermal method,and the effects of different short chain alcohol/water on the structure and electrochemical properties of electrode materials were studied.Moreover,the prepared electrode materials were modified by high-gravity liquid-phase exfoliation.The main research contents are as follows:（1）Basic study on the chain length and structure of solvents in the preparation of Ni-Co LDH by solvothermal method.Under magnetic stirring,effects of chain length and solvent structure on the morphology of the short-chain saturated monoethanol were studied.For chain length,the aqueous solutions of methanol/water,ethano/water l,n-propyl alcohol/water and n-butyl alcohol/water were selected as solvents;For the structure of the solvent,selecting aqueous solutions of n-propyl alcohol/water and isopropanol/water,n-butyl alcohol/water,sec.-butyl alcohol/water,isobutanol/water and tert.-butyl alcohol/water as solvents;Thereinto,V_alcohol/ V_water=7:3,The molar ratio of nickel to cobalt is 4:1.Finally,the solvent with best electrochemicalperformance was selected to study the effect of the ratio of alcohol to water and the ratio of nickel to cobalt on the electrochemical properties of the material.The physical properties were characterized by X ray diffraction（XRD）,scanning and transmission electron microscope（SEM and TEM）and surface area analyzer（BET）;The electrochemical performance was tested by electrochemical workstation and blue battery test system.The results show that when the solvent is tert-butanol aqueous solution,The layered structure is obtained and uniformly grew on the carbon cloth In addition,when V_alcohol/V_water=7:3,the molar ratio of nickel to cobalt is 5:1were the best operating condition with the specific capacity is almost constant,But,the rate performance increased to 70.8%.（2）Basic study on the number of hydroxyl groups in solvents when preparing Ni-Co LDH by solvothermal method.Exploring saturated polyols as solvents,effect of the number of hydroxyl groups on the morphology of the prepared Ni-Co LDH,and test ang analyze the physical properties and electrochemical properties of the Ni-Co LDH electrode materials.Among them,Polyols choosed ethanol/water and ethylene/water glycol,n-propyl alcohol/water,1,2-propanediol/water and propanol/water,n-butyl alcohol/water and butanedio/water l with V_alcohol/V_water=7:3 and the molar ratio of nickel to cobalt is 4:1.Finally,we choosed the solvent with the best electrochemical performance to study the effect of ratio of alcohol to water and the molar ratio of nickel to cobalt on the electrochemical properties of materials.Material characterization by means of XRD、SEM、TEM and BET;The electrochemical performance was tested by electrochemical workstation and blue battery test system.According to the results,the specific surface area of LDH-3 is 225.2 m²g^-1,average pore size is 8.16 nm and has better electrochemical performance;Meanwhile,It is found that the increase of the number of hydroxyl groups could result a significant decrease in electrochemical performance.In addition,When V_alcohol/V_water=6:4 and the best molar ratio is 1:1,obtained the best operating condition for the preparation of electrode materials with the specific capacity up to 1083.6 C g^-1 at the current density of 2 A g^-1.（3）Exfoliation of LDH-3A in high gravity field.In the beaker,exploring the effect the concentration of exfoliating agent and exfoliating time on electrochemical properties of materials;In the high gravity field,that is to say,in the high gravity rotated packing bed,studing the effects of residence time and high gravity factor on the electrochemical properties of the materials.By comparing the electrochemical properties obtained by exfoliating in beaker and high gravity field,it’s found that the electrode material obtained by exfoliating with the high gravity rotated packing bed has achived performance optimization,whose specific capacity is as high as 1354.5 C g^-1 at 5 A g^-1,and at 1146.2 C g^-1 at 30 A g^-1,meanwhile,rate performance(5-30 A g^-1)is 84.6%.Besides,asymmetric supercapacitors assembled with a maximum energy density of 45.0 Wh Kg^-1,corresponding to power density is 361.0 W Kg^-1;the maximum power density is 4961.3 W Kg^-1,corresponding to the energy density is 30.5 Wh Kg^-1,significantly better than the supercapacitor with the unexfolited and exfoliated in beaker.Apparently,the high gravity rotated packing bed has enhanced mass transfer,It is beneficial to the realization of exfoliation.