尖晶石LiMn₂O₄的制备及其电池制作技术与性能研究

【作者】 姚耀春；

【导师】 戴永年；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2005， 博士

【摘要】 随着电子设备的快速发展以及能源与环境问题的日益突出,人们对化学电源提出了更高的要求。锂离子电池以其高电压、比能量大、循环寿命长,无污染等优点而得到广泛的应用。具有高插入电位的过渡金属氧化物常用作锂离子电池的正极材料,目前研究较多的是层状结构的LiCoO₂、LiNiO₂以及尖晶石结构的LiMn₂O₄。其中尖晶石LiMn₂O₄以其高电压、高安全性、低成本、易回收、对环境友好等优点而被人们公认为最具应用前景的锂离子电池正极材料之一。 本文在综述锂离子电池及其相关材料的基础上,分析了国内外尖晶石LiMn₂O₄的研究现状,可知LiMn₂O₄正极材料的不足之处在于原料的混合均匀性不好,结构不稳定,容量衰减快和循环可逆性差。尽管许多研究工作者做了大量的研究,开发了溶胶-凝胶法、融盐浸渍法、Pechini法等来制备LiMn₂O₄正极材料,并使材料的性能在一定程度上有所提高,但由于这些方法不是工艺复杂,就是成本较高,不适于大规模化生产。因此研究开发既能应用于工业化生产,又能制备出具有优良性能的尖晶石LiMn₂O₄的工艺路线依然是当前研究工作的重中之重。 为了既能适应工业化生产需要,又能改善材料性能,本文在传统固相合成法的基础上,引入机械活化的方法,采用机械活化—固相合成法制备尖晶石LiMn₂O₄正极材料,并采用离子掺杂和表面包覆对其进行改性研究。在此基础上对锂离子电池的制作技术和性能进行了研究,并试制了10Ah锂离子动力电池。采用TG、DSC、XRD、SEM、EDS、ICP-AES、AAS等检测手段和电化学分析方法相结合,对材料的热力学性质、物理化学性能以及电池性能进行了分析研究。 LiMn₂O₄合成原料的热分析表明,合成尖晶石LiMn₂O₄正极材料的总反应由三个分步反应组成,即Li₂CO₃的分解、MnO₂的分解以及Li₂O与Mn₂O₃的合成反应。采用机械活化—固相合成法可以提高原料的混合均匀性,降低反应温度,稳定晶体结构,改善产物性能。 在湿法球磨—固相合成法四因素三水平正交实验中,影响LiMn₂O₄电化学性能的主次因素依次为合成温度、Li/Mn摩尔比、球磨时间和恒温时间。合成原料以Li₂CO₃为锂源和EMD为锰源较好。烧结气氛为氧气时产物的性能较好,并对其物理和化学两方面的作用机理进行了分析。适当的制团压力可以增加颗粒的接触面积,促进反应的进行,但过大的压力会阻碍气体的溶解和扩散,从而延缓反应的进行。先加Li₂CO₃球磨的混料方式可以减小原料的粒度差,提高混料的均匀性,所以材更多还原

【Abstract】 With the rapid development of electronic facilities as well as energy and environmental concerning, people make high demands on batteries. Lithium-ion batteries are widely used for their favorable advantages of high voltage, big specific capacity, long cycling life and non-pollution. Transitional metal oxides with high inserted potential are usually used as cathode material of Li-ion batteries. At present, layered compounds LiCoO₂, LiNiO₂ and spinel LiMn₂O₄ are extensively studied. Spinel LiMn₂O₄ is considered as one of the most promising cathode materials for Li-ion batteries because of its high voltage, high safety, low cost, easy recycling and environmental affinity among these materials.Based on summarizing Li-ion batteries, some correlative materials and analysing the status quo about spinel LiMn₂O₄ research domestic and abroad, it’s known that the deficiency of the material lies in inhomogeneity, instability, fast fading as well as poor reversibility. Now, many preparation methods,such as sol-gel, welt-impreghation and Pechini method have been used to synthesize LiMn₂O₄ cathode material by reserchers. To some extent, the properties of the material are improved. Nevertheless, these methods are not used for mass production because of complicated technics or high cost. So the emphasis of our investigations is to develop a techniques that can both be fit for industrialization and synthesize LiMn₂O₄ with excellent performances.For adapting to the need of industrialization and improving the properties of materials, the method of mechanical activation has introduced on the basis of traditional solid state reaction. The spinel LiMn₂O₄ cathode material was prepared by the mechanical activation—solid state synthesis method, and was modified by ion doping and surface coating. The producing technique and performances of lithium-ion batteries were studied, the 10Ah power lithium-ion batteries were trial-produced on the basis of the material synthesized. The thermodynamic property, the physical-chemistry characteristics and the performances of batteries were analysed by means of thermogravimetry（TG）, differential scanning calorimetry（DSC）, X-ray diffraction （XRD）, scanning electric microscopy（SEM）, energy dispersive spectrometer （EDS）, inductively coupled plasmas-atomic emission spectroscopy （ICP-AES）, atomicabsorption spectrum （AAS） as well as various electrochemical analysis methods.The thermal analysises of LiM^C^ synthesis materials show the overall reaction is composed of three reactions, namely the decomposition of Li2CO3, the decomposition of MnC>2 as well as the composition of LijO and Mn2C>3. The mechanical activation — solid state synthesis method can enhance rawmaterial homogeneity, reduce reaction temperature, stabilize crystalline structure and improve product performances.The main factors influencing LiM^C^ electrochemical properties are synthesis temperature, Li/Mn mole ratio, ballmilling time and retenion time in turn through four factors and three levels perpendicular experiments of the hydro-ballmilling—solid state synthesis method. Compared with different reaction reagents, the Li2CO3 is batter Li source and electrolytic MnO2 is batter Mn source. When the sintering atmosphere is O2, the performances of products are batter, and the mechanism of physical and chemic action is analysed. Appropriate briqutting pressure can increase contact area and accelerate reaction, but excessive pressure may hinder the dissolution and diffusion of gas, which will postpone reaction rate. The mixing method firstly added Li2CC>3 can reduce the particle size difference and homogeneity of raw materials, thereby attaining the best discharge specific capacity 129.12mAh/g. The materials synthesized by two steps solid state reaction have preferable performance. Comparing the two continuous calcination method with the two discontinuous calcination, the former is the better.Ultrasonic technique was firstly applied to prepare spinel LiM^C^ cathode material, and the effects of different ultrasonic conditions on the performances of spinel LiMn2O4 were investigated. Compared with hydro-ballmilling, the mechanical activating effect is stronger, which is profit for accelerating nucleation and controlling crystal growth. The samples disposed by ultrasonic have well formed crystal shape and particle distribution. With the increase of frequency, power and time, the electro-chemical performances of products are improved. Ultrasonic cavitation effect is enhanced in turn from distilled water, absolute ethanol to acetone in different medium, respectively.The lattice parameter reduced and the average valence of manganese increased when Co or Cr cation doped in LiM^Cv As the doping cotent increases, the dischargespecific capacity of samples is reduces, but the structural stability and cycle performance are improved. Although F-doped samples have higher specific capacity, the increase of Jahn-Teller distortion and Mn dissolution lead to poor cycle performance. The materials have not only high reversible capacity but also well cycleability by F-Co or F-Cr ion co-doping. The properties of LiCo0.09Mn1.91O3.92F0.08 cathode material are best, the specific capacity is 119.16mAh/g, the capacity loss is 2.79% after 20th cycle.The well clad coated on parent material can be synthesized by a sol-gel method, the materials modified consist of exterior clad, doping transition layer and interior parent material. LiCoCVcoated LiCo0.09Mn1.91O392F0.08 powers with smooth appearance improve the resist ability of corrosion and decrease the dissolution of Mn to electrolyte. With the L1COO2 content increasing, the specific capacity and cycle performance of samples are improved. The capacity fading rate is 3.57% after 50th cycle capacity at 55 °C high temperature, so the capacity loss is suppressed distinctly.Also, the composition and production technique of Li-ion batteries were discussed, the influence of important working procedures （including slurrying, coating, assembling, forming, etc.） on battery performance was analysed.and the main materials used were optimized. The 083448 prismatic lithium-ion battery was produced, the cathode material was LiCoO2/LiMn2O4 composite material, the anode material was carbonaceous mesophase spheres（CMS）, the electrolyte injected was 1 M L1PF6 in a mixture of ethylene carbonate （EC） and dimethyl carbonate （DMC） at the volume ratio of 1:1. The battery have well rate and temperature characteristics, excellent cycle life （the capacity loss is 5.41% after 300 cycles）, lower internal resistance and reliable security, which have achieved the performance requirements of the same kind battery.The lOAh tentative battery was produced by self-making electrode winder for power lithium-ion batteries, the core prerared by the machine have well overlap, flatting and compactness. The testing results show that the power battery has higher specific energy density（the volume energy density is 181.74Wh/L, the mass energy density is 111.57Wh/kg） and preferable cycleability（the capacity loss is 1.38% after 15 cycles at 0.5C rate, the capacity loss is 7.39% after 46 cycles at 1C rate）.更多还原