| Vanadium pentoxide(V2O5)is a kind of transition metal oxide with layered structure,which has high lithium insertion potential.When used as the lithium ion battery cathode material,V2O5 has advantages of high theoretical specific capacity and low cost.However,the poor ion transport capability and electronic conductivity impede the practical application of V2O5.To overcome the above drawbacks,three kinds of V2O5/nitrogen-doped graphene nanocomposites were designed and fabricated in this article.The structure and the morphology of these composites were characterized by XRD,XPS,Raman spectroscopy,nitrogen adsorption-desorption technique,SEM and TEM.The electrochemical behavior was investigated by cyclic voltammetry,constant current charge/discharge and electrochemical impedance spectroscopy.Then the structure-function relationship was studied to enhance the lithium storage properties.V2O5·nH2O nanowires/N-Graphene composite was fabricated by a liquid-phase method.Then V2O5·nH2O was converted to orthorhombic V2O5 by heat treatment and the V2O5 nanowires/N-Graphene composite was obtained.The introduction of nitrogen-doped graphene can not only provide high conductivity,but also anchor the nanowires to prevent them from agglomeration.Benefiting from the above properties,the electrochemical performance can be enhanced efficiently.Specific capacities of 273,242,206,181 and 161 mAh g-1 are obtained at 100,200,500,1000 and 2000 mA g-1,respectively.V2O5/3DNG composite was fabricated by a hydrothermal method and the following heat treatment.The V2O5 nanoparticles are embedded in 3D nitrogen-doped graphene network,which can not only provide high conductivity,but also enhance the electrolyte invasive capability.Meanwhile,the 3D porous structure can facilitate the migration of Li+.After cutting and tableting,the V2O5/3DNG can be used as the cathode electrode directly without the usage of binders,conductive agents and conductive current collectors.This V2O5/3DNG free-standing cathode has excellent rate and cycle behaviors.Specific capacities of 290,268,238,206 and 162 mAh g-1 were delivered at 100,200,500,1000 and 2000 mA g-1,respectively.Even after 500 cycles at a current density of 1000 mA g-1,a reversible specific capacity of 134 mAh g-1 can still be obtained.VO2 hollow spheres synthesized by solvothermal method were wrapped by nitrogen-doped graphene and oxidized to orthorhombic V2O5 by heat treatment,then V2O5 hollow spheres/nitrogen-doped graphene(VOSH/NG)composite was obtained.In VOHS/NG composite,V2O5 hollow spheres are assembled from ultra-thin nanosheets,which is beneficial for mitigating the volume change in charging/discharging processes.Meanwhile,the thin shell composed of ultra-thin nanosheets can enhance the infiltration capability with the electrolyte and improve the ion transport capability.Moreover,the existence of nitrogen-doped graphene can improve the conductivity and structure stability.When used as lithium ion battery cathode material,the reversible capacities of VOHS/NG composite are 287,254,231,203,and 164 mAh g-1 at current densities of 100,200,500,1000,and 2000 mA g-1,respectively.The hollow structure has the potential as carrier.Meanwhile,V2O5 has excellent lithium polysulfide anchoring capacity.Hence,VOHS/NG composite is furtherly used as the sulfur host of lithium-sulfur batteries.The large specific surface area of the nitrogen-doped graphene can rapidly adsorb lithium polysulfides V2O5 hollow spheres can furtherly anchor the lithium polysulfide by chemical process.As a result,VOHS/NG composite can effectively inhibit the shuttle effect of lithium polysulfide.In addition,the introduction of nitrogen-doped graphene can not only improve the conductivity,but also effectively buffer the volume change during the electrochemical processes together with the hollow structure of V2O5.Reversible capabilities of 1488,1140,1040,924,and 746 mAh g-1 can be delivered at 0.1 C,0.2 C,0.5 C,1 C,and 2 C,respectively. |
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