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Synthesis,structure And Electrochemical Performance Of Layered-spinel Integrated LiNi0.5Mn0.5O2-LiMn1.9Al0.1O4 Composite Cathodes For Lithium Ion Batteries

Posted on:2018-07-24Degree:MasterType:Thesis
Country:ChinaCandidate:M J TianFull Text:PDF
GTID:2321330515484441Subject:Chemistry
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In recent years,due to environmental pollution and energy shortage,the energy materials have received considerable attention.Among all the energy storage devices,lithium ion batteries had been extensively studied owing their unique advantages,such as high-security,no memory effect and high power density.LiNiO2,as a typical layered cathode material,exhibits a high specific capacity of 200 mAh g-1 and good security;however,its poor structural stability limits the commercialization application of the material.In order to improve the structural stability,Mn3+ has been introduced into LiNiO2 to form the LiNi0.5Mn0.5O2 with good structural stability;however,LiNi0.5Mn0.5O2 still exhibits relative low discharge capacity.On the other hand,as a promising cathode material,spinel lithium manganese oxide of LiMn2O4 is extensively investigated owing to its low cost,high abundance reserves,safety and environmental friendliness.However,the fast capacity decay during charge-discharge process hinders the practical application of LiMn2O4-based materials.It has been frequently reported that Al-modified LiMn1.9Al0.1O4 cathode materials present outstanding cycle performance due to the larger band energy of Al-O than that of Mn-O.Recently,multi-component integrated composite cathode materials(e.g.,layered-layered,layered-spinel,etc.)have attracted considerable attention for high-capacity LIBs.In this thesis,the integrated layered-spinel xLiNi0.5Mn0.5O2-(1-x)LiMn1.9Al0.1O4 cathode materials were prepared,and the effects of the composition,sintering temperature and pH value on the structure,micromorphology and electrochemical performance of the integrated materials were studied in detail.The main results are listed as following:(1)The layered-spinel cathode materials of xLiNi0.5Mn0.5O2-(1-x)LiMn1.9Al0.1O4(LNM-LMA-x)were synthesized by a sol-gel method,and their structures,micromorphology and electrochemical performance were investigated in detail.With x increasing,the samples are changed from hexagonal to cubic symmetry.The layered LiNi0.5Mn0.5O2 and spinel LiMn1.9Al0.1O4 co-existence in the integrated materials with x = 0.25-0.75.All the samples are composed with nano-sized particles and obtained a minimum value of ~130 nm at x = 0.5.Furthermore,when x = 0.5,the electrode exhibits the high initial discharge capacity(0.1C,236 mAh g-1),relatively good rate performance and structural stability.(2)The layered-spinel cathode materials of 0.5LiNi0.5Mn0.5O2-0.5LiMn1.9Al0.1O4(LNM-LMA-0.5)were prepared by a sol-gel method.The effects of sintering temperature(Ts)on their structures,micromorphology and electrochemical performance were investigated in detail.The sintering temperature has no obvious effect on the structures of materials.All the materials possess co-existence of hexagonal and cubic phase with Ts increasing.The initial discharge capacities change from 165 mAh g-1 to 245 mAh g-1 as Ts increases from 500 ? to 900 ?.When Ts = 700 ?,the LNM-LMA-0.5 electrode exhibits the highest initial discharge capacity(0.1C,245 mAh g-1),relatively good rate performance and structural stability.(3)The layered-spinel cathode materials of 0.5LiNi0.5Mn0.5O2-0.5LiMn1.9Al0.1O4(LNM-LMA-0.5)were prepared by a sol-gel method.The effects of pH on the structures,micromorphology and electrochemical performance were investigated in detail.As pH increases from 6 to 8.5,all the materials exhibit co-existence of hexagonal and cubic phase.The initial discharge capacities vary from 171 mAh g-1 to 255 mAh g-1 with pH increasing from 6 to 8.5.When pH = 7,the LNM-LMA-0.5 electrode obtains the highest initial discharge capacity(0.1C,255 mAh g-1),relatively good rate performance and structural stability.
Keywords/Search Tags:Lithium-ion battery, LiNiO2, LiMn2O4, Layered-spinel composite, Cathode material, Electrochemical performance
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