Study Of Layere Double Hydroxide Used For High-Performance Supercapacitor Electrodes

Layered Double Hydroxide(LDH)is an ideal supercapacitor electrode material because its large theoretical specific surface area can provide electric double layer capacitance and transition metal on its sheet acts as active sites for the electrochemical reaction.However,due to the hydrogen-oxygen bond between the LDH sheets,the LDH material often agglomerates severely,and the conductivity of the LDH is poor,which affects its electrochemical energy storage performance.Aiming at solving agglomeration problem of LDH,this paper constructs hollow microspheres composed of LDH nanosheets based on the idea of micro/nano structure design,and obtains an electrode material with large specific surface area,which can expose more active areas,thus take advantage of its high pseudocapacitance.In view of the poor conductivity of LDH,this paper builds a hierarchical nanocomposite by combining LDH with nitrogen-doped reduced graphene oxide with good conductivity,which can increase the conductivity of the composite to some extent.It inhibits the agglomeration of LDH and achieves the purpose of synergistically improving its electrochemical performance.The main contents of this paper are as follows:1,Through sol-gel method and phase separation,polyethylene oxide(PEO)was used as soft template to prepare uniform Al2O3 hollow microspheres.Then,using the Al2O3 hollow microspheres as the hard template,the NiAl-LDH hollow microspheres were prepared by microwave assisted hydrothermal method.The effects of hydrothermal temperature and reactant ratio on the morphology of the final product were investigated in detail.The relationship between the morphology and electrochemical properties of the product was investigated,and the optimal reaction temperature and reactant ratio were determined.The LDH hollow microsphere successfully retains the high specific surface area and proper pore size of the Al2O3 template,with high specific capacitance(1578 F g-1 at 1 A g-1)and excellent cycle stability(The specific capacitance retention rate after 10,000 cycles at 20 A g-1 is 93.75%).In addition,an asymmetric supercapacitor based on this LDH hollow microsphere as the positive electrode was assembled and can achieve a high energy density of 20 Wh kg-1.2.Using melamine as the nitrogen source,nitrogen-doped reduced graphene oxide was successfully prepared by a simple heat treatment.NiCo-LDH/nitrogen-doped reduced graphene oxide nanocomposites were obtained by microwave assisted hydrothermal method.The hydrophilicity and conductivity of the graphene-based plate are improved by nitrogen doping.By regulating the nitrogen-doping level of graphene,the controlled deposition of LDH with different densities was realized,and the influence of the above parameters on the electrochemical properties of composite was studied.The composite has a high specific capacitance(1720 F g-1 at 3 A g-1)and good cycle stability(83%retention after 10,000 cycles at 20 A g-1).In addition,the maximum energy density of an asymmetric supercapacitor assembled based on the composite as the positive electrode can reach 31.2 Wh kg-1.