Preparation And Theoretical Study Of Carbon Material And NiCo-LDH Electrode Material

Supercapacitors have the outstanding advantages of high power density and long cycle life,but it is difficult for their electrode materials to have high energy density at the same time,which has restricted their industrial application.This article uses a combination of theoretical calculations and experiments to study the improvement of capacitance performance by modifying carbon nanotubes and Ni Co-LDH materials.First principles were used to study the effects of doping on the electrical properties,quantum capacitance and surface stored charge of carbon nanotubes,and to explore the effects of different electrolyte and electrolyte concentration on the quantum capacitance of carbon nanotubes.In addition,Ni Co-LDH electrode materials were prepared by electrodeposition method,and the specific capacitance,rate performance,and cyclic stability of the materials were improved by adjusting the electrodeposition solution.A hybrid supercapacitor with carbon nanotubes as negative electrode and Ni Co-LDH as positive electrode was prepared.The main research contents are as follows:（1）According to first-principles calculation,in the doping system,boron doped carbon nanotubes（B-CNT）and nitrogen doped carbon nanotubes（N-CNT）have the smallest doping energy and the most stable structure,and the adsorption of H⁺or OH^-contributes to the stability of the carbon nanotube structure.Based on the analysis of quantum capacitance（C_Q）and surface stored charge（Q）,the quantum capacitance of B-CNT reaches its maximum value in the acidic electrolyte under negative bias.The quantum capacitance of N-CNT reaches its maximum in the high concentration alkaline electrolyte under positive bias.The Q value of boron-doped carbon nanotubes adsorbated 5 hydrogen ions at-1V was 77.89μC cm^-2,which was 284.26%higher than that of Pure-CNT(20.27μC cm^-2).The Q value of nitrogen-doped carbon nanotubes adsorbated 5 hydroxyl ions at 1V was 95.83μC cm^-2,which was increased by 309.35%compared with the original carbon nanotubes(23.41μC cm^-2).Therefore,B-CNT is suitable to be used as cathode material of for asymmetric supercapacitors in acidic electrolytes,and the higher the electrolyte concentration,the better the energy storage capacity of the materials.N-CNT is suitable for anode material for asymmetric supercapacitors in high concentration alkaline electrolytes.（2）Nickel-cobalt hydroxide（Ni Co-LDH）electrode material was prepared by cyclic voltammetry deposition on carbon paper substrate.By adding acetate solution into the deposition solution to reduce the deposition current,the agglomeration phenomenon of electrode materials was improved,and the electrochemical performance was improved.The specific capacitance of Ni Co-LDH at 5 A g^-1is 1066.67 F g^-1.By exploring the different ratios of Ni²⁺and Co²⁺in the deposited solution,it is found that when the nickel-cobalt ratio is2:1,the size of the Nickel-cobalt hydroxide（Ni₂Co₁-LDH）electrode material is the smallest,that is,the area of contact with electrolyte ions is larger,thus showing excellent electrochemical performance.At 1 A g^-1,the specific capacitance of Ni₂Co₁-LDH electrode material can reach 1927.11 F g^-1.When the current density increases from 1 A g^-1to 10 A g^-1,the specific capacitance of Ni₂Co₁-LDH retains 85.33%.After 5000 cycles at 5 A g^-1,the specific capacitance of Ni₂Co₁-LDH is retained 86.41%.（3）Ni₂Co₁-LDH（X）electrode material was prepared by electrodeposition of activated carbon paper with different concentrations of KOH on the basis of Ni₂Co₁-LDH material.Nickel-cobalt hydroxide（Ni2Co1-LDH（1））electrode material based on 1M KOH activated carbon paper has high specific capacitance(up to 2255.56 F g^-1at 1 A g^-1)and good rate performance(increasing from 1 A g^-1to 10 A g^-1,specific capacitance retention 89.36%).In the prepared symmetric supercapacitor,the specific capacitance of Ni₂Co₁-LDH（1）at 1 A g^-1is 92.62 F g^-1.A hybrid supercapacitor with Ni₂Co₁-LDH（1）as positive electrode and carbon nanotubes as negative electrode was prepared.In hybrid supercapacitors,Ni₂Co₁-LDH（1）//BCNT devices have excellent coulomb efficiency at low current density,indicating good capacitance characteristics and excellent specific capacitance,which is 77.58 F g^-1at 1 A g^-1.At 2 A g^-1,charge and discharge 3000 times,its specific capacitance retention 96.8%.