Preparation And Electrochemical Properties Of Nano-structured Molybdenum Oxide

With the development of society and the continuous growth of energy demand,new energy storage systems and technologies are becoming more and more important to human beings.As a major breakthrough in the field of energy storage,lithium-ion secondary batteries have attracted the attentions of scientists.Due to its low cost,long cycle life,high energy density and good reversibility,it has been widely used for energy storage.However,with the rapid promotion of electric vehicles and various portable electronic devices,higher requirements have been put forward for lithium-ion energy storage systems.The design and preparation of advanced electrode materials have become one of the research directions of the lithium ion energy storage system.It has become one of the keys of improving the performance of lithium ion batteries to design and prepare anode materials with stable structure,high specific energy and superior safety characteristics.Due to the abundant and variable chemical valence and morphology of Mo-based metal oxides,the stability of the overall material structure can be greatly enhanced,and the conductivity and lithium storage properties of the material can be improved.Therefore,the nanostructure molybdenum-based oxide and its composite materials have a changce to replace the traditional graphite to become an ideal anode material for lithium ion battery system.Based on the introduction of nanostructured materials,the molybdenum oxide with binary and ternary structure as the research object,the molybdenum oxides and its complexes with various nanostructure morphologies were explored and used as anode materials with superior specific capacity and good performance for lithium ion batteries.The major progresses are listed as follows:In this paper,molybdenum-based lithium ion anode materials,such as MoO₃,MoO₂,SnMoO₄ and FeMoO₄ were studied.The preparation,synthesis,crystal structure,composite modification and electrochemical properties of molybdenum-based anode materials were explored in detailed.1.Using molybdate as the molybdenum source,MoO₃ hexagonal nanosheets were prepared by a simple calcination process under normal pressure in air.The size was uniform and the morphology was controllable,the width is about 200-300 nm and the thickness is about 50 nm.A variety of characterization methods were used to analyze and test its battery performance.When the prepared MoO₃ sample is used as a negative electrode material for LIBs,at a current density of 100 mA g^-1,the initial discharge specific capacity of the MoO₃ electrode material is 489 mAh g^-1 and the charge specific capacity is 365 mAh g^-1.After 50 cycles,the charge and discharge specific capacities were maintained at 156 and 155 mAh g^-1,respectively.At the same time,in order to increase the theoretical specific capacity of the material,we modified the material by carbon coating.As the anode material of lithium ion battery,its electrochemical performance has been improved.The first charge capacity of MoO₃@C electrode material reached 859 mAh g^-1.After circulating to 80 cycles,the sample capacity was stable at 497 mAh g^-1.And the cycle stability has been greatly improved.Therefore,the electrochemical properties of MoO₃@C material have been improved after the carbon coating modification of the material.2.MoO₂/graphene nanocomposites were prepared by a simple solvothermal method.The lithium storage performance and mechanism as lithium ion battery anode materials were studied.The nano-MoO₂/graphene composite has a high reversible discharge capacity of 721 mAh g^-1 at a current density of 200 mA g^-1,and its capacity retention rate reaches 100%.The superior capacity and cyclic stability of the MoO₂/graphene material are attributed to the unique hierarchical structure of MoO₂nanocrystals and lamellar graphene.MoO₂ nanocrystals?30⁸0 nm?are grown in situ on graphene-based bodies and can be used in lithium ion battery.The influence of the buffer volume effect during the insertion/extraction of ions effectively prevents the powder from being pulverized during the charge and discharge cycle,exhibiting high specific capacity,good rate performance and cycle stability.3.The new nanosheet?-SnMoO₄ was synthesized by a simple synthetic route of solid state reaction?SSR?,which has the good crystal morphology and first applied in the electrode of lithium ion battery.The nanostructures were studied by DFT,XRD,Raman,FT-IR,SEM,TEM,SAED and XPS analysis,and their electrochemical properties were tested.At the current density of 200 mA g^-1,the charge and discharge specific capacity is 1224.6 and 1329.8 mAh g^-1,respectively,and the steady-state specific capacity can still reach 400 mAh g^-1 after 300 cycles.4.Through a simple hydrothermal method,the controllable synthesis of FeMoO₄nano-powder can be achieved by adjusting the type and amount of solvent and the temperature of hydrothermal reaction.The crystal phase of the nanostructures was analyzed by XRD,and the morphology and size of the nano-powders were observed by SEM and TEM.It can be found that type and amount of solvent and surfactant,temperature of reaction have an important on morphology,particle size and electrochemical performance of FeMoO₄ nanomaterials.