The Research Of Vanadium Dioxide And Its Modified Materials As A Positive Electrode Applied In Lithium-ion Capacitor Battery

With the increase of market demand for new energy vehicles and various electronic products,the development of energy storage devices with high power and high energy density is particularly urgent.Lithium-ion batteries（LIBs）can provide high energy density but limited power density in various energy storage systems;compared to LIBs,supercapacitors have high power density and excellent cycling stability due to surface or near-surface charge storage behavior.However,their energy density is low.In this case,the lithium-ion capacitive battery emerges as the times require.The device combines the advantages of lithium-ion batteries and supercapacitors are assembled from a battery-type electrode and a capacitive electrode.Its high power density and high energy density make a research hotspot in recent years.Vanadium-based transition metal oxides are rich in structure due to their different atomic configurations and various vanadium valence states,providing superior lithium storage capabilities.In particular,vanadium dioxide（VO₂）has a layered structure and large interlayer spacing,which is beneficial for li-ion intercalation and removal.However,the conductivity of the material is poor and the diffusion coefficient is low.It is easy to dissolve vanadium during charge and discharge,so its rate performance and cycle performance need to be further improved.In addition,in recent years,vanadium dioxide is usually used as a cathode material for lithium ion batteries and shows a high specific capacity,but its application in lithium ion capacitive batteries is relatively scarce.A pure phase VO₂（B）was prepared in this paper and modified as cathode ion capacitive batteries.The following work was carried out:（1）A three-dimensional self-assembled spherical structure VO₂（B）was first synthesized by a simple hydrothermal method and applied as a cathode material to lithium-ion capacitive battery devices.The as-prepared materials were characterized by structural tests to determine the special structure of VO₂（B）and exhibit excellent performance of 200 m Ah g^-1at the first charge/discharge.（2）Co cations were introduced on the basis of pure phase VO₂（B）.Metal cation doping can improve the electronic conductivity and cycling stability of vanadium oxides.The lithium ion capacitor battery is constructed with the pre-lithiated activated carbon（AC）as the negative electrode.When the power density is 185 W kg^-1,the energy density can reach 26 Wh kg^-1.（3）Carbon nanotubes（CNTs）were used as carbon sources and combined with the prepared VO₂（B）.In this study,VO₂（B）@CNTs spheres were well structured,in which they were embedded in the whole microspheres.This unique structure carbon nanotubes to improve the ionic and electronic conductivity of vanadium dioxide.Apply it to lithium-ion capacitor batteries,obtain a maximum energy density 101.13 Wh kg^-1.