富锂锰基正极材料的形貌与结构调控及电化学性能研究

发布时间：2018-01-14 08:20

本文关键词：富锂锰基正极材料的形貌与结构调控及电化学性能研究　出处：《哈尔滨工业大学》2017年博士论文　论文类型：学位论文

【摘要】：富锂锰基材料具有放电容量大、原料成本低等优点,被认为是下一代高能量密度、低成本锂离子电池的重要候选正极材料。针对富锂锰基正极材料电导率偏低、倍率性能差、电压衰减等问题,本文制备了不同形貌、不同组分、不同结构的富锂锰基材料,对材料进行了复合、改性,逐步深入研究了材料颗粒形貌、多相组成晶体结构、局部精细结构与材料电化学性能的构效关系。采用共沉淀法制备Mn_(4/6)Ni_(1/6)Co_(1/6)CO_3前驱体,通过高温烧结制备双层中空球形结构Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2材料,研究了材料形貌的演化机理以及形貌对材料电化学性能的影响规律。研究发现,引入NH_4HCO_3大幅提高了前驱体晶粒生长速率,颗粒内部结晶度低于颗粒表面结晶度,颗粒在高温烧结过程中发生不连续收缩,由实心结构向核壳结构再向双层中空多孔结构转变。双层中空球形结构富锂锰基材料表现出比实心结构材料更高的电化学性能,在1、3、5、10C倍率下,其放电比容量分别达到223、196、170、132mAhg-1,在3C下循环400次的容量保持率为87.6%。材料优异的倍率性能归因于双层中空多孔结构使Li+离子易于扩散至材料内部结构。同时,稳定性高的多级微纳结构及均匀混合的锰钴镍多元素组成有利于材料提高循环稳定性。采用水热法结合高温烧结与组分控制,制备了一系列具有三维多级结构以及层状-尖晶石多相组分的富锂锰基材料。研究了三维多级结构的生长机理、多相组分晶体结构对材料电化学性能的影响规律。研究表明,三维多级结构由一维实心棒状向二维平面再向三维空心组装体扩展。通过高温烧结与组分控制,制备的多级层状-尖晶石富锂锰基材料由六方R-3mLiTMO_2、单斜C_2/mLi_2MnO_3以及立方Fd-3mLiMn_(1.5)Ni_(0.5)O_4三种晶体结构组成。XRDRietveld精修结果表明,材料晶胞体积随尖晶石组分含量增大而增大。复合适量尖晶石组分的材料在1、2、5、10C下,放电容量分别达到251、227、202、155mAhg-1,其Li+离子扩散系数由1.69×10-13提高至7.74×10-13cm2s-1。材料优异的电化学性能归因于三维微纳多级结构有利于Li+离子脱嵌,适量尖晶石组分可增大材料晶胞体积,为材料提供三维Li+离子扩散通道。采用真空抽滤法结合烧结处理,设计制备了高负载量自支撑CNT/尖晶石混合导电层改性Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2材料。研究表明,CNT可提高材料电子电导率,有效解决富锂锰基材料颗粒在充放电循环过程中发生破碎并与导电剂脱离的问题。经烧结处理后,材料中Mn元素在CNT基体中发生热还原反应,使材料原位生成尖晶石相。尖晶石相可进一步将材料的Li~+离子扩散速率由2.53×10-13cm2s-1提高至1.08×10-12cm2s-1。自支撑混合导电层改性材料的首次放电比容量与库伦效率分别为304mAhg-1与91.7%;在1、3、5、10C下,其放电比容量分别达到266、238、215、166mAhg-1;在3C下循环400次的容量保持率为87.7%。材料电化学性能的提高归因于CNT具有长程、连续的三维电子传输网络,提高了材料的电子电导率;尖晶石组分的原位复合改性可为材料提供快速的Li+离子三维扩散通道,提高了材料的离子电导率。采用水热法对Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2材料进行表面结构调控,利用XRDRietveld精修方法、同步辐射X射线显微成像技术、同步辐射X射线吸收精细结构谱、高角度环形暗场扫描透射电子显微成像技术,研究了材料表面原子尺度晶体结构、局部精细结构与材料电化学性能的构效关系。结果表明,原始材料中Ni元素在颗粒表面(200)R晶面发生选择性富集,使颗粒表面晶体结构由六方层状转变为立方岩盐相,产生厚度约3nm的Ni/Li混排层。对材料进行水热处理可有效消除该Ni/Li混排层,晶胞混排比例由3.52%减小至1.35%;此外,水热处理有效增大了材料晶胞c轴及晶胞体积。水热处理材料的首次放电比容量为301mAhg-1,库伦效率为90.7%,在1、3、5、10C下,其放电比容量为248、201、163、133mAhg-1;1C下循环200次后,水热处理使材料的放电比容量由原始材料的158提高至227mAhg-1,平均放电电压由3.16V提高至3.41V。材料优异的倍率性能与稳定循环性归因于材料水热处理后被抑制的表面Ni/Li混排层、增大的Li层层间距及晶胞体积。
[Abstract]:Lithium rich manganese based materials with large discharge capacity, low cost of raw materials, is considered to be the next generation of high energy density, low cost of candidate cathode material for lithium ion batteries. The conductivity of lithium rich manganese based cathode materials is low, poor rate performance, voltage decay and other issues, this paper prepared with different morphologies and different components, lithium rich manganese based materials with different structures, the composite materials were modified, gradually in-depth study of the material composition of particle morphology, crystal structure, structure-activity relationship of local fine structure and electrochemical performance of material. By using co precipitation method to prepare Mn_ (4/6) Ni_ (1/6) Co_ (1/6 CO_3) precursor, preparation of double-layer hollow spherical structure through high temperature sintering of Li_ (1.2) Mn_ (0.54) Ni_ (0.13) Co_ (0.13) O_2 material, sound evolution mechanism of material morphology and morphology on the electrochemical properties of materials affect the study. The study found that the introduction of NH_4HCO_3 is greatly increased. High precursor grain growth rate, internal particle crystallinity is lower than that of particle surface crystallinity, particle in high temperature sintering process in continuous contraction, from solid structure to the core-shell structure to the change of double hollow porous structure. The double-layer hollow spherical structure of lithium rich manganese based materials exhibit higher electrochemical properties than solid structure materials and at 1,3,5,10C, the discharge capacity reached 223196170132mAhg-1, 400 cycles the capacity under the 3C retention rate performance of 87.6%. material with excellent due to the double-layer hollow porous structure of Li+ ions that internal structure is easy to spread to the material. At the same time, the multistage high stability micro nano structure and nickel manganese cobalt evenly mixed many elements can improve the cycle stability. Materials with high temperature sintering and components by hydrothermal method. The preparation of a series of 3D structure and multi - layered Spinel lithium rich manganese based multiphase materials. Research on the growth mechanism of 3D multi structure, multi phase group influence points of crystal structure on the electrochemical performance of the material. The results show that the three-dimensional hierarchical structure consists of one-dimensional solid rod to two-dimensional to three-dimensional hollow assembly expansion. Controlled by high temperature sintering and components. Lithium rich manganese based materials by six R-3mLiTMO_2 multi layered spinel stone preparation, monoclinic C_2/mLi_2MnO_3 and cubic Fd-3mLiMn_ (1.5) Ni_ (0.5) O_4 three crystal structure refinement.XRDRietveld results show that the material with spinel crystal volume content increases. The amount of composite component of spinel materials under 1,2,5,10C and the discharge capacity reached 251227202155mAhg-1, the Li+ ion diffusion coefficient by the electrochemical performance of 1.69 * 10-13 to 7.74 * 10-13cm2s-1. material with excellent due to the multi-level three-dimensional micro node The Li+ is conducive to the ion deintercalation amount of spinel component can increase the material volume while providing three-dimensional Li+ ion diffusion channel material. Combined with sintering treatment by vacuum filtration method, design and fabricate a high load of free-standing CNT/ spinel mixed conductive layer modified Li_ (1.2) Mn_ (0.54) Ni_ (0.13) Co_ (0.13) O_2 materials. The results show that CNT can improve the electronic conductivity material, effectively solve the lithium rich manganese based materials particles broken and conductive agent detachment in the charge discharge cycle process. After sintering treatment, Mn element material thermal reduction reaction in the CNT matrix, the in situ formation of spinel materials spinel phase. Further Li~+ ion diffusion rate of material from 2.53 * 10-13cm2s-1 to 1.08 * 10-12cm2s-1. to improve the self supported hybrid conductive layer of the modified materials were 304mAhg-1 and 91.7% of the first discharge specific capacity and efficiency in Kulun; 1,3, 5,10C, the discharge capacity reached 266238215166mAhg-1; 400 cycles the capacity retention rate of 3C in the electrochemical performance of 87.7%. increase due to CNT has long range, three-dimensional electronic transmission network continuously, improve the electronic conductivity of the material; spinel composition in situ composite modified Li+ can provide 3D ion diffusion channel fast as the material, improve the ionic conductivity of the material. The Li_ by hydrothermal method (1.2) Mn_ (0.54) Ni_ (0.13) Co_ (0.13) O_2 material surface structure control, using XRDRietveld refinement method, synchrotron radiation X ray imaging technology, synchrotron radiation X ray absorption fine structure, high angle annular dark field scanning transmission electron microscopy imaging technology, the research of atomic scale surface crystal structure, structure-activity relationship of local fine structure and electrochemical properties. The results show that the Ni element of raw materials In the particle surface (200) crystal face of R selective enrichment, the particle surface crystal structure by six layered into cubic rock salt phase, produce the thickness of about 3nm Ni/Li mixed layer. The material for water heat treatment can effectively eliminate the Ni/Li mixed layer, cell mixing ratio from 3.52% to 1.35%; in addition, hydrothermal treatment can increase the material crystal c axis and the cell volume. The first discharge water heat treatment material than the capacity of 301mAhg-1, Kulun efficiency was 90.7%, in 1,3,5,10C, the discharge capacity is 248201163133mAhg-1; 1C after 200 cycles, the water heat treatment so that the discharge capacity of the material from the original material 158 to 227mAhg-1, average discharge voltage by mixed layer rate performance and stability of circulating 3.16V increased to 3.41V. material with excellent surface attribution Ni/Li was inhibited in hot water treatment material, increase the Li level spacing and cell volume.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM912

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