Preparation And Application Of Ni₃V₂O₈@carbon-based Composite Material In Supercapacitor

The rapid development of science and technology has brought about severe energy crisis and great environmental damage.There is an urgent need to develop a highly efficient and environmentally friendly electrochemical energy storage system.Supercapacitor is a new type of energy storage device which has the characteristics of both traditional capacitor and chemical battery and makes up for their shortcomings.The development of low-cost,high-efficiency,green and safe electrode materials is a major research hotspot in response to the needs of modern society and to deal with emerging ecological problems.Compared with carbon materials（activated carbon,carbon nanotubes,graphene,etc.）and conductive polymers（polyaniline,polypyrrole,polythiophene,etc.）,bimetal oxide materials have higher energy density and power density.However,its conductivity and stability can not meet the needs of high-performance energy storage devices,so researchers mainly modify and optimize the bimetal oxide materials by means of nanocrystallization and composite,in order to develop new supercapacitors with high efficiency and high quality.This thesis focuses on the application of Ni₃V₂O₈ materials and their composites in supercapacitors.The main research contents and achievements are as follows:1.Ni₃V₂O₈ materials with different morphologies were prepared by one-step hydrothermal method.The pseudo-capacitance properties of electrode materials with different morphologies were studied by changing the morphology of Ni₃V₂O₈materials.When ethanolamine was used as the structure directing agent,3D flower-like Ni₃V₂O₈was obtained.The flower-like structure composed of intertwined nano-flakes makes Ni₃V₂O₈ have interconnected ion diffusion channels.The flower-shaped open structure maximizes the exposure of the active surface,which is beneficial to improve the electrochemical performance.The specific capacitance of flower-shaped Ni₃V₂O₈ is as high as 810 F·g^-1 at 1 A·g^-1 and the capacitance retention is 64.34%after 10,000 cycles at 10 A·g^-1.2.A new three-dimensional（3D）flower-shaped Ni₃V₂O₈@CNTs is further designed and constructed by a simple one-step hydrothermal method.The results show that the synergistic effect and the flower structure gives the synthesized Ni₃V₂O₈@CNTs ultra-high specific capacitance(1054 F·g^-1,1 A·g^-1),and the excellent rate performance(89%after 10,000 cycles at 10 A·g^-1).In addition,when Ni₃V₂O₈@CNTs and rice husk activated carbon are assembled into asymmetric supercapacitors,the device has ultra-high energy density and high power density(45.5 Wh·kg^-1,at 795W·kg^-1 and 16.0 k W·kg^-1 at 30 Wh·kg^-1),and the capacitance retention rate is 81%after10,000 cycles at 10 A·g^-1,showing excellent cycle stability.3.Prepare Ni₃V₂O₈@graphene nanomaterials.Using Ni（NO₃）₂·6H₂O and NH₄VO₃ as metal sources,graphene was prepared by electrochemical stripping as carbon source,and Ni₃V₂O₈@graphene was obtained by reaction in ethylene glycol solution.Scanning electron microscope and transmission electron microscope analysis shows that Ni₃V₂O₈ nanoparticles were anchored on graphene sheets with uniform size.At 1 A·g^-1 current density,the specific capacitance of Ni₃V₂O₈@graphene is as high as1664.2 F·g^-1.After 10,000 consecutive charges and discharges at 10 A·g^-1,the capacitance retention is as high as 91.2%.Asymmetric supercapacitor was assembled with rice husk activated carbon as negative active material and Ni₃V₂O₈@graphene as positive active material,and its electrochemical performance and battery performance were tested.At the power density of 805 W·kg^-1,the energy density is as high as 48.3Wh·kg^-1.