Synthesis,Modification And Electrochemical Mechanism For Vanadates Anode Materials And LiMn_1/3Co_1/3Ni_1/3O₂ Cathode Materials

Fossil fuels are the most widely used energy resource worldwide.Risks related to resource depletion,environmental pollution,and political unrest with regard to fossil fuel production have led to the rapid emergence of a variety of intermittent renewable and cleaner energy sources such as wind,solar and wave.In order to integrate these renewable energies into the electrical grid,a large-scale energy storage system(ESS)is vital to peak shift operation.Among various energy storage technologies,using an electrochemical secondary battery is a promising method for large-scale storage of electricity due to its flexibility,high energy conversion efficiency,and simple maintenance.Lithium ion battery are considered as the best candidate of power sources.Meanwhile,it is very necessary to develop high performance lithium/sodium ion battery electrode materials.In this paper,a series of vanadates anode materials(Mo V₂O₈,MnV₂O₆,Co₃V₂O₈,and FeVO₄)are synthesized via a solvothermal(or hydrothermal)process followed by thermal treatment.A facile co-precipitation combined hydrothermal method is used to synthesize Li Ni_1/3Co_1/3Mn_1/3O₂ nanosheets.Then XRD,in-situ XRD,ex-situ XRD,XPS,SEM,(HR-)TEM,Raman,and electrochemical performance testers were used to study the relationship between the physical character and the electrochemical properties of the electrode material,formation mechanism of the sample morphology,and lithium storage mechanism.The main contents are listed as follows:(1)FeVO₄@Ti O₂ nanocomposite was fabricated via a simple and cost-effective approach.The FeVO₄ nanorods were synthesized by a hydrothermal method combined with calcination route without using any template and then coated with Ti O₂ through an annealing process of dihydroxybis titanium.The FeVO₄nanocomposite has a significantly enhanced electrochemical performance by coating with Ti O₂.Compared with pure FeVO₄,FeVO₄@Ti O₂ shows a better rate performance.The amorphous Ti O₂ coating on a layer of FeVO₄ created efficient improved stability of the structure during the charge/discharge process.The excellent rate capability and cyclic stability of the sample proved that FeVO₄@Ti O₂ could be used as a new anode for lithium ion battery application.The synthesis method can also be applied to synthesize other related materials with typical morphologies and properties.FeVO₄/r GO nanocomposites are synthesized by a facile hydrothermal method.Benefiting from the carbon based materials,which can improve the electrode conductivity and efficient buffering the volume change.As an anode material,the FeVO₄/r GO nanocomposites exhibit excellent lithium storage properties.The promising performance is attributed to the good electrical transport from the intimate contact between FeVO₄ and graphene oxide.This work indicates that the FeVO₄/r GO composite is a promising anode for high performance lithium storage.(2)MnV₂O₆/r GO nanocomposites are synthesized by a facile hydrothermal method.Benefiting from the carbon based materials,which can improve the electrode conductivity and efficient buffering the volume change.As an anode material,the MnV₂O₆/r GO nanocomposites exhibit excellent lithium storage properties.The promising performance is attributed to the good electrical transport from the intimate contact between MnV₂O₆ and graphene oxide.This work indicates that the MnV₂O₆/r GO composite is a promising anode for high performance lithium storage.(3)We demonstrate that the preparation of graphene oxide(GO)decorated Co₃V₂O₈ to form(Co₃V₂O₈/r GO)composite through a facile approach combining hydrothermal synthesis with thermal reduction.The resulting Co₃V₂O₈/r GO exhibits excellent electrochemical performances in LIBs.The ideal performance is attributed to the good electrical transport from the intimate contact between Co₃V₂O₈ and graphene oxide.This work indicates that the Co₃V₂O₈/r GO composite is a promising anode for high-performance lithium storage.Hollow micro-/nanostructures have great potential in the development of electrode materials by promoting the ion transport and mitigating the volume change.Double-shelled Co₃V₂O₈hollow nanosphere are synthesized by a facile solvothermal combined thermal treatment method.Meanwhile,two other architectures of hollow nanosphere and nanoparticle can be easily acquired via change the annealing temperatures.As an anode material,Benefiting from the desired hollow structure,the double-shelled Co₃V₂O₈hollow nanosphere exhibited excellent lithium storage properties,stable cycle performance,and high rate capability.The hollow nanostructures can efficiently enhanced contact area of the electrolyte/electrode interface to promote the transmit of electrons and lithium ions,which can slow down the capacity loss during long cycles.(4)Vanadium-based mixed oxides are promising for high-energy-density lithium-ion batteries(LIBs)due to their abundant oxidation states,complex chemical compositions and synergistic effects,but the large volume change upon lithiation/delithiation limits the electrochemical properties.Two-dimensional nanostructures have great potential in the development of electrode materials by promoting the ion transport and alleviating the volume change.Herein,porous Mo V₂O₈nanosheets are synthesized via a solvothermal process followed by thermal treatment.Benefiting from the nanosheet structure with large surface area and abundant pores,the Mo V₂O₈ electrode exhibits impressive lithium storage properties with superior rate performance and prolonged cyclability.Furthermore,the lithium storage mechanism of the Mo V₂O₈nanosheets is investigated by in-situ X-ray diffraction,ex-situ X-ray diffraction and X-ray photoelectron spectroscopy measurements,which confirms the synergistic effects of Mo and V upon lithiation/delithiation process.In addition,a full cell consisting of the Mo V₂O₈nanosheets and commercial Li Fe PO₄exhibited good electrochemical performance,demonstrating that the Mo V₂O₈nanosheets ia an promising anode material for LIBs.(5)We have fabricated self-assembled Li Ni_1/3Co_1/3Mn_1/3O₂ nanosheets via a facile synthesis combining co-precipitation with the hydrothermal method.Scanning electron microscope(SEM)images showed that the self-assembly processes for the Li Ni_1/3Co_1/3Mn_1/3O₂ nanosheets depending on the reaction time and temperature.As a cathode material,the Li Ni_1/3Co_1/3Mn_1/3O₂nanosheets have efficient contact with the electrolyte and short Li⁺diffusion paths,as well as sufficient void spaces to accommodate large volume variation.The nanosheets are beneficial to inproving diffusion of Li⁺in the electrode.In addition,a full cell consisting of the porous Mo V₂O₈nanosheets and Li Ni_1/3Co_1/3Mn_1/3O₂nanosheets exhibited good electrochemical performance.From these results,the Li Ni_1/3Co_1/3Mn_1/3O₂ nanosheets have potential as cathode for LIBs,although further optimization is needed to improve their performance to meet the demands of practical applications.