Preparation And Electronchemical Performance Of Lithium Manganese Nanomaterials

With the development of science and technology,Lithium ion batteries as the most efficient portable electron installations has been used in lots of mobile electronic devices.Such as ipad,smart phone,digital cameras,etc.and expected to be future used in electric vecheils,hybrid vehicles,milltary and aerospace,however,the traditionals cathode materials have some problems at present,for instance,environmental aspects,safty,cost,the Lithium ion batteries no longer able to meet the high efficiency,high energy and other aspects of more pressing needs.So the cathode materials Li Mn₂O₄and Li Mn_1.5Ni_0.5O₄ which have spinel strcture and high-voltage are able to meet the demands.Due to low cost,safe,and rich in manganese of the earth,Li Mn₂O₄ and Li Mn_1.5Ni_0.5O₄,have become the research hotspots in lithium-ion battery cathode material.But these two materials still have the following disadvantages:the dissolution of element manganese ions in electrolyte and Jahn-Teller effect restrict its application in power lithium ion batteries.Thus,how to improve the electrochemical stability of LiMn₂O₄ and Li Mn_1.5Ni_0.5O₄ has been a hot research topic.In this thesis,the nanowire,sphere and sheet structure LiMn₂O₄ and nanorod Li Mn_1.5Ni_0.5O₄ were prepared by solid-state method?By the X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,it can be proved that the microstructure,size and morphology of the Li Mn₂O₄ and Li Mn_1.5Ni_0.5O₄.The electrochemical performanceofthesamplewasinvestigatedbyelectrochemical measurement.The results are as follows:Firstly,Mn O₂ nanowire was prepared by the molten salt method.We used the glucose as a carbon source,the composite materials Mn O₂@C was prepared by hydrothermally,which could coat and grow different mass carbon layer,MnO₂@C and Li OH co-grinding and mixing well.Then the lithium manganese oxides materials have been synthesized via a high-temperature solid-phase method.By the XRD and SEM,it can be proved that the morphology of the lithium manganese oxide?Li Mn₂O₄?is boll.Testing its electrochemical properties,The results show that Li Mn₂O₄@10%C nanowires with a diameter of 50-100 nm can be obtained by sintering at 750?for 8 h in air atmosphere.The prepared Li Mn₂O₄@10%C has good electrochemical performance.The specific capacity was 103 mAh/g.after 500 cycles,and the relative initial specific capacity was maintained at 90%.On the basis of solid-phase of Li Mn₂O₄@10%C nanowires,Mn₂O₃sphere and Mn O₂ sheet were prepared as another precursors for LiMn₂O₄sphere and sheete materials.Then we characterized their electrochemical properties.The spherical and flaky Li Mn₂O₄ materials prepared by same method at 750?for 8 h in air atmosphere which are verified the morphology of the precursor and the final product can be maintained by modifying the carbon coating layer.The initial dis-charge capacities of sheets and spherical Li Mn₂O₄ materials are about 118.4 mAh/g and 86.5mAh/g,and the corresponding coulomb efficiencies are 82.3%and 64.4%,when glvanostatic charge-discharge tests at 0.1 C at room temperature.Finally,the spinel Li Mn_1.5Ni_0.5O₄ electrode material was prepared on the basis of LiMn₂O₄ prepared by solid phase method,and prepared by controlling the reaction time,and carbon layer thickness process conditions.The results show that nanorod-like Li Mn_1.5Ni_0.5O₄@15%C was prepared by using MnO₂@15%C as the precursor at 750?and 8 h in air atmosphere,The results of XRD and electrochemical tests show the final product has a stable structure and high crystallinity.It has a voltage platform higher than spinel Li Mn₂O₄ is around 4.7 V.After cycling 100 cycles at a current density of 1 C,the specific capacity of the material remains at 97.87%.