锰基层状富锂氧化物正极材料的合成、表征及改性研究

发布时间：2018-02-28 15:41

本文关键词： 锂离子电池锰基层状富锂氧化物不可逆失氧可逆容量循环稳定性　出处：《华南理工大学》2014年博士论文　论文类型：学位论文

【摘要】：为了满足电动汽车续航里程的需求，锂离子电池的能量密度需要进一步提高，而限制其提高的主要因素就是商业化正极材料的比容量较低。锰基层状富锂氧化物在2-4.8V范围内的可逆容量超过200mAh g-1，是最有发展前景的正极材料。但是，锰基层状富锂氧化物还有很多问题需要解决，比如不可逆容量损失大、循环性能差、倍率性能低。针对这些问题，本论文提出了几种新的合成方法，制备出系列锰基层状富锂氧化物材料，用扫描电子显微镜、X-射线衍射、拉曼光谱、交流阻抗、恒电流充放电等方法，详细研究了制备材料组成、结构和电化学性能。论文的主要内容包括：（1）利用聚乙烯吡咯烷酮(PVP)和乙二醇(EG)的协同分散机制，合成出尺寸均匀的锰基层状富锂氧化物Li[Li1/3-2x/3Mn2/3-x/3Nix]O2(x=0.3)，该氧化物在0.1C的放电容量为205mAh g-1，循环60圈后的容量保持率为87%，容量衰减的主要原因是部分过渡金属离子失去了电化学活性；（2）考察了锂前驱体用量对锰基层状富锂氧化物化学组分、晶体结构及电化学性能的影响，结果表明，适当降低锂用量可以提高材料的可逆容量，但会降低其循环稳定性，过低的锂用量会导致相分离，使材料容量降低；（3）提出了快速蒸发法，合成出具有低结构缺陷的锰基层状富锂氧化物Li[Li1/3-2x/3Mn2/3-x/3Nix]O2(x=0.5)，该氧化物在0.05C循环50圈，，几乎无容量衰减，在1C循环300圈，容量保持率在80%以上；（4）提出了自导引化学合成法，构筑出具有微-纳结构的锰基层状富锂氧化物Li[Li1/3-2x/3Mn2/3-x/3Nix]O2（x=0.5），该氧化物在0.05C的放电容量为222mAh g-1，循环50圈后的容量保持率为93%，在2C的放电容量达到110mAh g-1；（5）研究了Co3+取代对锰基层状富锂氧化物Li[Li0.2Ni0.2-x/2Mn0.6-x/2Cox]O2电化学性能的影响，结果表明，Co3+取代能够显著提高材料的不可逆失氧和充放电容量，但是会明显降低材料的容量稳定性和电压稳定性；（6）考察了Fe3+取代对锰基层状富锂氧化物Li[Li0.2Ni0.13Mn0.54Co0.13]O2电化学性能的影响，发现Fe3+取代会严重降低材料的可逆容量，但是对Co3+的取代可以抑制材料在循环过程中的电压衰减；（7）研究了化学组分与合成温度对锰基层状富锂氧化物xLi2MnO3-(1-x)LiCoO2首次充放电性能的影响，发现充电容量的最大值出现在x=0.6，而放电容量的最大值出现在x=0.4～0.5；当合成温度为800℃时，材料的首次充电过程是一个两步反应过程，而当合成温度为900～1000℃时，是一个三步反应过程；（8）研究了不同类型阳离子M（M=Co3+, Ni3+, Cr3+, Fe3+,[Ni0.5Mn0.5]3+）在锰基层状富锂氧化物Li[Li0.2Mn0.4M0.4]O2首次充放电过程中的氧化还原行为，以及对材料充放电性能的影响，结果表明，当M=Co3+时，Li[Li0.2Mn0.4Co0.4]O2的不可逆失氧很强，当M=Ni3+，Li[Li0.2Mn0.4Ni0.4]O2的充电斜区容量很高，当M=Cr3+时， Li[Li0.2Mn0.4Cr0.4]O2的失氧量很低，当M=[Ni0.5Mn0.5]3+时，Li[Li0.2Mn0.4(Ni0.5Mn0.5)0.4]O2的充电斜区容量和充电平台容量介于Li[Li0.2Mn0.4Co0.4]O2与Li[Li0.2Mn0.4Ni0.4]O2之间，当M=Fe3+时，通过溶胶凝胶法在900℃煅烧出的Li[Li0.2Mn0.4Fe0.4]O2不具有传统意义上的“锰基层状富锂氧化物”结构，在充电过程中没有表现出失氧平台，而且充放电容量很低，此外，M3+(M=Ni, Cr,[Ni0.5Mn0.5]3+)取代Co3+都可以提高Li[Li0.2Mn0.4Co0.4-xMx]O2的可逆容量。上述研究为锰基层状富锂氧化物的优化设计及性能提高提供新的研究思路和理论基础，丰富锂离子电池材料制备方法和构效关系的内容。
[Abstract]:In order to meet the demand of the electric vehicle mileage, the energy density of lithium-ion batteries need to be further improved, and the main factors that restrict the commercialization of cathode materials is to improve the low specific capacity. The reversible capacity of manganese oxide in the layered Li rich 2-4.8V range more than 200mAh g-1, is one of the most promising cathode materials but. The shape of rich manganese base, there are many problems to be solved such as lithium oxide, irreversible capacity loss and poor cycle performance and rate performance is low. To solve these problems, this paper puts forward some new synthesis methods, preparation of lithium rich manganese oxide material series base shape, with a scanning electron microscope, X- ray diffraction, Raman AC impedance spectroscopy, and galvanostatic charge discharge method, a detailed study of the preparation of material composition, structure and electrochemical properties.
The main contents of this paper include: (1) using polyvinylpyrrolidone (PVP) and ethylene glycol (EG) synergistic dispersion mechanism, the synthesis of uniform size manganese layered rich lithium oxide Li[Li1/3-2x/3Mn2/3-x/3Nix]O2 (x=0.3), the oxide in the discharge capacity of 0.1C 205mAh g-1, after 60 cycles the capacity keeping rate 87%, the main reason of capacity fading is part of the transition metal ions lost electrochemical activity; (2) investigated the amount of precursors of lithium manganese base - rich chemical group lithium oxide, effect, crystal structure and electrochemical performance of the results, appropriate to reduce the amount of lithium can improve the reversible capacity of the materials, but will reduce the cycle stability, low dosage of lithium can lead to phase separation, the material capacity is reduced; (3) put forward a fast evaporation method, the synthesis of manganese base shape with low structural defects in lithium rich oxide Li[Li1/3-2x/3Mn2/3-x/3Nix]O2 (x =0.5), the 0.05C oxide in 50 cycles, almost no capacity attenuation, 300 cycles in 1C, the capacity retention rate of 80% or more; (4) the homing chemical synthesis method, constructed with manganese base like micro nano structure of lithium rich oxide Li[Li1/3-2x/3Mn2/3-x/3Nix]O2 (x=0.5), the oxide in the discharge capacity 0.05C 222mAh g-1, maintained after 50 cycles the capacity rate of 93%, up to 110mAh g-1 in the discharge capacity of 2C; (5) to study the effects of Co3+ substitution on the electrochemical properties of lithium manganese base - rich oxide Li[Li0.2Ni0.2-x/2Mn0.6-x/2Cox]O2, the results show that Co3+ substitution can significantly improve the irreversible loss of oxygen and charge discharge capacity of the material, but significantly reduces the capacity and voltage stability of materials; (6) the effects of Fe3+ substitution on the electrochemical properties of lithium manganese base - rich oxide Li[Li0.2Ni0.13Mn0.54Co0.13]O2, Fe3+ substituted Would seriously reduce the reversible capacity of the materials, but the voltage decay substitution for Co3+ can inhibit the material in the circulation process; (7) to study the chemical composition and temperature on the synthesis of lithium rich manganese base layered oxide xLi2MnO3- (1-x) LiCoO2 first charge discharge performance, find the maximum charge capacity in x=0.6 however, the discharge capacity reached the maximum at the x=0.4 ~ 0.5; when the synthesis temperature is 800 degrees centigrade, the material for the first time the charging process is an two step process, and when the synthesis temperature is 900~1000 degrees centigrade, is a three step process; (8) to research the different types of cationic M (M=Co3+ Ni3+, Cr3+, Fe3+, [Ni0.5Mn0.5]3+), redox behavior in lithium rich manganese base type oxide Li[Li0.2Mn0.4M0.4]O2 first charge discharge process, and the influence of the charge and discharge performance of materials. The results showed that when M=Co3+, Li[, Li0.2Mn0.4Co0.4]O2 and irreversible The loss of oxygen is very strong, when the M=Ni3+, charging capacity of Li[Li0.2Mn0.4Ni0.4]O2 cable is very high, when M=Cr3+, the oxygen loss of Li[Li0.2Mn0.4Cr0.4]O2 is very low, when M=[Ni0.5Mn0.5]3+, Li[Li0.2Mn0.4 (Ni0.5Mn0.5) 0.4]O2 between the charging capacity and charge capacity of the petroclival region between Li[Li0.2Mn0.4Co0.4]O2 and Li[Li0.2Mn0.4Ni0.4]O2 platform, when M=Fe3+, by sol-gel method at 900 DEG C calcined Li[Li0.2Mn0.4Fe0.4]O2 has not the traditional sense of "layered rich lithium manganese oxide structure during the charging process showed no loss of oxygen, and the charge discharge capacity is very low, in addition, M3+ (M=Ni, Cr, [Ni0.5Mn0.5]3+) instead of Co3+ can improve the reversible capacity of Li[Li0.2Mn0.4Co0.4-xMx]O2.
The above research will provide new research ideas and theoretical foundation for the optimization design and performance improvement of manganese rich lithium rich oxides, and enrich the contents of preparation methods and structure activity relationship of lithium ion battery materials.

【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

【共引文献】