The Preparation Of Transition Metal Oxides/Carbon Nanocomposites And Their Application For Lithium Ion Battery

Rechargeable lithium ion batteries have been widely studied and applied as excellent secondary green energy in recent years.With the development of portable electronic equipments,the traditional graphite anode could'nt meet the needs of large market of lithium ion battery,and lithium ion anode material is an important part of the batteries,which played an important role in improving the performance.Therefore,exploring new anode materials with high capacity and cyclic stability has become the main direction of researches.Transition metal oxides?TMOs?,which have 2-4 times capacities higher than that of graphite and environmental friendliness,have attracted much attention.It has become an effective solution to design nano-structure units or carbon nanocomposites through various methods.Considering the cost and difficulty of preparation,it is necessary to seek excellent materials and methods for large-scale production and application.In addition,the design of flexible and light-weight electrode materials has become the tendency to the next generation of lithium ion batteries.The main work of this thesis was to prepare transition metal oxide and porous carbon nanocomposites for lithium ion batteries anode materials.The specific research contents mainly included the following three parts:1.CoO/LSC nanocomposites were obtained by loading flower-like CoO on the surface and pores of porous loofash sponge carbon material?LSC?through water bath synthesis and calcining.The preparation method was simple,low cost and easy to synthesize for large-scale.During charging/discharging of the lithium ion battery,porous carbon can effectively relieve volume stress of CoO and increase the conductivity.The discharge capacity maintained 781 mAh g^-1 when the current density was 0.2 A g^-1,which was much higher than that of traditional graphite.It showed excellent cycle and rate performance.This work may provide a broad research idea for the full utilization of wastes.2.Fe-MOFs were used as self-sacrificing templates.Fe-MOFs were uniformly loaded on the surface of GO through oil bath process firstly,then Fe-MOFs were transformed into Fe₂O₃/Fe₃O₄ nanoparticles wrapped in carbon layer by a novel triethylamine combustion method.SEM and TEM showed that porous Fe₂O₃/Fe₃O₄@C octahedrons were uniformly attached to the surface of graphene?G?foam.The porous structures not only alleviate the volume deformation of nanoparticles,but also effectively increase the contact area with electrolyte.The formation of graphene foam also increases specific surface area and electrical conductivity.When it was applied to lithium ion battery,the reversible discharge specific capacity still maintained 635 mAh g^-1 under 5 A g^-11 after 400 cycles,indicating excellent electrochemical properties.This porous Fe₂O₃/Fe₃O₄@C/G nanocomposite has a potential application,and the unique method might also provide a new thought for the preparation of metal oxide and carbon composites.3.Melamine foam is cheap and contains lots of nitrogen element.It is still flexible after carbonization.Co₃O₄ nanorods formed by triethylamine burning were vertically grown on nitrogen-doped carbon foam?NCF?to form NCF/Co₃O₄ nanocomposites.During the combustion process,the precursor could be successfully transformed while the carbon foam remained flexible and unaffected.Co₃O₄ nanorods also had lots of porosity,which were conducive to preventing large volume change in the charging/discharging process.At the same time,nitrogen-doped 3D carbon foam as the substrate provided good conditions for high loading of Co₃O₄,enhanced electron transmission rate and direct electrical contact.When it was directly used as a self-supporting electrode without binder,the discharge capacity was still 576 mAh g^-1at 1 A g^-1,it proved that the excellent cycle performance was still maintained under a high loading.To some extent,the problems of low charge transfer impedance and easy separation caused by the addition of traditional inactive electrode materials were eliminated.