Transition Metal Vanadium Oxides:Synthesis And Electrochemical Performance

Nowadays lithium ion battery has played a great role in electrical device and electrical vehicle.To enhance the limited performance of lithium ion battery from low theoretical capacity of commercial carbon anode,novel anodes with high rate and long cyclic life are demanding.The transition metal oxides,which involve multiple electron transfer reactions to provide higher capacity than that of carbon,have received more and more attentions.The two metals in ternary transition metal oxide anode have an interfacial and synergistic effect during the electrochemical process,and to a certain extent,its cycling stability is enhanced.However,the electrochemical performance of ternary transition metal oxide is still hindered by its low electrical conductivity and large volume expansion.The emergence of nanotechnology and nanomaterials provides an effective route of optimization,which promotes the development of energy storage and conversion devices with improved energy and power densities.To address the problems associated with large volume expansion and low electrical conductivity of vanadium oxides,we propose two methods to prepare ternary transition metal vanadium oxide nanomaterials as anodes of lithium ion batteries.The effects of synthesis conditions on the crystal structures and electrochemical performances of these anodes are investigated.The followings are detailed contents and results.?1?The highly crystallized Zn₃V₂O₇?OH?₂·2H₂O microflowers assembled by nanosheets with a high specific surface area of 43.8 m²/g are synthesized via a simple liquid phase method at room temperature.The results of X-ray diffraction and scanning electron microscopy show that,based on the Ostwald ripening mechanism,the addition of ethylene glycol effectively reduces the growth rate of crystal nucleation and improves the crystallinity of Zn3V2O7?OH?2·2H2O.As anode of lithium ion battery,the Zn3V2O7?OH?2·2H2O delivers a high capacity of 1287 mAh/g,and exhibits a long-term cyclic stability with a capacity of 931 mAh/g after 140 cycles and good rate performance with a capacity of 501 mAh/g at 5 A/g.A capacity of 272 mAh/g can be achieved after 400 cycles at 10 A/g.These results indicate that the high crystallinity and nanosheets structure of Zn₃V₂O₇?OH?₂·2H₂O anode have positive effects on the improvement of its electrochemical performance.X-ray photoelectron spectroscopy and X-ray diffraction are utilized to reveal Li⁺insertion/extraction mechanism,including intercalation,alloying and conversion.The smaller particles evolved from nanosheets after cycling could facilitate the lithium-ion transport and provide more reaction sites.?2?Amorphous iron vanadium oxide nanoparticles are synthesized through hydrothermal process followed by solid phase sintering.The transition metal ions adsorb onto the oxygen-containing functional groups of the graphene oxide to form nucleation.Untrasmall nanoparticles precursor of iron vanadium oxide is produced via nucleation process.The surface energy of nanomaterials is effectively reduced with the presence of graphene oxide.The precursor is sintered under air atmosphere to remove graphene and obtain amorphous iron vanadium oxide nanoparticles with a size of 40-50 nm.As anode of lithium ion battery,the amorphous iron vanadium oxide nanoparticles electrode can deliver a high capacity of 483 mAh/g after 1600 cycles at a current density of 5 A/g.What's more,the initial coulombic efficiency of amorphous iron vanadium oxide nanoparticles electrode can achieve as high as 83%,which could be attributed to its low surface defects and therefore,reduced side reaction with electrolyte.