【作者】 彭庆文；

【导师】 唐致远； 刘兴江；

【作者基本信息】 天津大学 ， 应用化学， 2010， 博士

【摘要】 采用氢氧化物共沉淀前驱体高温固相反应制备了层状LixNi1/3Co1/3Mn1/3O2(0.95≤x<1.20)正极材料,应用ICP-OES、AAS对材料进行了成分分析,并采用XRD、晶格精修、SEM、DSC以及充放电测试表征了Li:(Ni+Co+Mn)比对材料结构和性能的影响。结果表明:x≥1.00时,随x值的增大,峰I003/I104的比值R、首次放电比容量及DSC峰值温度均呈现先增后减的趋势,并在x=1.05附近具有极大值;晶格精修表明阳离子混排率呈现先减后增的趋势,在x=1.08附近具有最小混排率。证明了阳离子混排对晶格参数、电性能和热稳定性存在重要影响。首次发现Li1+x[Ni0.4Co0.2Mn0.4]O2(x>0)系列材料中的大部分材料具有微波吸收特性。并应用其中的具有极强微波吸收特性的Li1.19Ni0.4Co0.2Mn0.4O2材料作为引发剂,首次成功地应用微波合成方法制备得到了Li1.05Ni1/3Co1/3Mn1/3O2材料。并对其相关性能进行了测试,结果显示微波法合成的Li1.05Ni1/3Co1/3Mn1/3O2材料具有良好的电化学性能和热稳定性能。首次成功地应用微波合成法制备了Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55)系列材料,并首次研究了过量Li+效应对Li1.2Ni0.2Mn0.6O2 (x=0)电化学性能的影响。XRD测试表明所合成样品均为a-NaFeO2结构,属R-3m空间群。随着锂含量的增加所得样品的晶格常数呈现线性递减趋势,这说明所得材料是性质均一的固溶体的。这预示着过量的Li+可能已经嵌入到Li1.2Ni0.2Mn0.6O2 (x=0)的过渡金属层中,并随着Ni2+逐渐向Ni3+的转变形成Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55)系列固溶体材料。应用XPS光电子能谱对所得样品进行扫描,发现随着锂含量的增加,Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55)系列材料中开始出现Ni3+并逐渐增多。充放电循环测试显示Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55)系列材料的首次充放电曲线、首次充放电效率以及循环性能都各不相同。Li1.2Ni0.2Mn0.6O2 (x=0)在2.0~4.8V电压范围内循环,首次放电比容量为219mAh/g,随着锂含量x的增大,首次放电比容量逐渐减低,但材料的循环性能得到了显著地提高。更多还原

【Abstract】 The layered cathode material of LixNi1/3Co1/3Mn1/3O2 (0.95≤x<1.20) has been prepared by using the co-precipitated (Ni1/3Co1/3Mn1/3)(OH)2 and Li2CO3 through solid reaction, ICP-OES and AAS were applied to analyze their compositions; XRD, Rietveld refinement, SEM, DSC and charge-discharge test were employed to characterize LixNi1/3Co1/3Mn1/3O2’s structure and performances. The results show that the ratio of I003/I104, the first discharge capacity and the highest peak temperature of DSC curves were all increasing first and then decreasing when 1.00≤x<1.20 and got their maximal value around x=1.05. Rietveld refinement shows that the ratio of cation mixing decreased firstly and then increased as 1.00≤x<1.20, and possessed the minimal value around x=1.08. Therefore, the cation mixing is a key factor which will affect the electrochemical performance, crystal cell parameter and thermal stability of the LixNi1/3Co1/3Mn1/3O2 cathode material.Most of Li1+x[Ni0.4Co0.2Mn0.4]O2(x>0)materials have firstly been found could absorb microwave. Thus, Li1.05Ni1/3Co1/3Mn1/3O2 was firstly prepared by a new simple microwave heating method using Li1.19Ni0.4Co0.2Mn0.4O2 as microwave absorber. The sample has excellent electrochemical properties and thermal stability.Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55) was firstly prepared by a new simple microwave heating method and the effect of extra Li+ content on electrochemistry of Li1.2Ni0.2Mn0.6O2 (x=0) was firstly revealed. X-ray diffraction identified that they had layered a-NaFeO2 structure (space group R-3m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li+ is possibly incorporated in structure of layered Li1.2Ni0.2Mn0.6O2 (x=0), accompanying oxidization of Ni2+to Ni3+ to form Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni3+ appeared and increased in content with increasing x value. Charge-discharge tests showed that Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55) truly displayed different electrochemical properties (different initial charge-discharge plots, capacities and cycleability). Li1.2Ni0.2Mn0.6O2 (x=0) in this work delivered the highest discharge capacity of 219mAh/g between 4.8 and 2.0 V. Increasing Li content (x value in Li1.2+x[Ni0.25Mn0.75]0.8-xO2 reduced charge-discharge capacities, but significantly enhancing cycleability.更多还原