Preparation And Electrochemical Performance Of Nickel Cobalt Based Hydroxide Composites

Nickel cobalt based hydroxide,as a highly potential positive electrode material for supercapacitors,has ultra-high specific capacitance and electrochemical activity,but its lower conductivity and stability limit its further development.Improving the conductivity and stability of materials by optimizing their structure and combining them with highly conductive materials is an effective way to solve this problem.Using ZIF-67 as the precursor,we designed and synthesized a composite material（C/N-NiCoMn-LDH/Ag）of carbon and nitrogen co doped nickel cobalt manganese hydroxide and metal silver,which effectively improved the poor structural stability of nickel cobalt based hydroxide.The energy storage mechanisms of different compositions of hydroxides and key factors affecting the electrochemical performance of materials were explored by combining characterization analysis and DFT theoretical calculations.Finally,a hybrid supercapacitor was constructed using C/N-NiCoMn-LDH/Ag electrode material and activated carbon to explore the practical application potential of the material.（1）Firstly,ZIF-67 precursor was synthesized by chemical precipitation method,and then coated with PDA.At the same time,Mn²⁺and Ag⁺sources were added,and additional positively charged ions were added to promote dopamine polymerization.Experiments and characterization analysis indicate that the weak alkaline environment of the dopamine polymerization system can also trigger the etching reaction of ZIF-67.With the extension of dopamine polymerization time,the material undergoes the evolution from solid,core-shell to hollow structures.Then,after heat treatment,the C/N-NiCoMn LDH/Ag composite was prepared by etching and deposition reaction with nickel nitrate.The NiCoMn-LDH nano sheet formed a hollow rhombic dodecahedron nano cage through self-assembly.This unique hollow nano cage structure has good structural stability,and can provide a wealth of electrochemical active site.（2）A study on the electrochemical performance of C/N-NiCoMn-LDH/Ag composite materials found that the specific capacitance of the material was as high as 1988 F·g^-1at a current density of 1 A·g^-1,and at a current density of 20 A·g^-1,it still had a specific capacitance of 1032 F·g^-1,demonstrating excellent rate performance.According to the DFT theoretical calculation results,with the introduction of Mn²⁺and Ag⁺sources,the crystallinity of the electrode material gradually decreases,the conductivity gradually increases.The adsorption energy of electrode materials for O*and OH*intermediates gradually increases,and they still have good adsorption performance at low temperatures.（3）In order to explore the practical application potential of electrode materials,hybrid supercapacitors and quasi solid supercapacitors were constructed using C/N-NiCoMn-LDH/Ag composite materials as cathode materials and activated carbon as anode materials.6 M KOH electrolyte and polyvinyl alcohol（PVA）based gel electrolyte were used as electrolytes respectively.The electrochemical performance of supercapacitors was studied within the temperature range of-30～25℃.The C/N-NiCoMn-LDH/Ag//AC HSC device can achieve energy densities of 39.60 Wh·kg^-1and 20.16 Wh·kg^-1at power densities of 825 W·kg^-1and 8250W·kg^-1,respectively.For the quasi-solid-state C/N-NiCoMn-LDH/Ag//AC HSC device,when the power density is 900 W·kg^-1and 4500 W·kg^-1respectively,the energy density can reach10.60 Wh·kg^-1and 3.33 Wh·kg^-1respectively,and both supercapacitors show good electrochemical stability at low temperatures.