锰系锂离子电池正极材料的研究

发布时间：2018-04-14 08:16

本文选题：锰酸锂 + 正极材料　；参考：《中国海洋大学》2014年硕士论文

【摘要】：锂离子电池作为储能材料被用于手机、照相机、手提电脑、电动车及混合动力汽车等领域。其中，锂离子电池的正极材料在其结构中占有举足轻重的地位。锰系氧化物锂盐正极材料因为其工作电压高，原材料丰富，价格便宜，安全性好，环境友好等优点，得到了广泛关注，在动力汽车等市场的具有很高的应用前景。但由于其较低的比容量，使用过程中容量衰减和循环性能差等原因，使其应用受到了一定的限制。通过阳离子取代锰离子的位置，对氧化锰锂进行掺杂形成固溶体，是提高氧化锰锂材料循环性能的重要方法。本论文采用共沉淀法，主要通过三种阳离子对锰酸锂进行了改性研究。利用X射线衍射仪（XRD），扫描电子显微镜（SEM）对材料晶体结构、表观形貌和化学成分进行了分析表征，以分析晶体的结构变化，颗粒的尺寸与形貌改变对材料性能的影响，从而优化材料的电化学性能；采用恒电流充放电测试技术对其电化学性能进行测定分析，探索最佳元素掺杂量。（1）通过研究锂离子对氧化锰锂的影响可以发现，随着锂离子含量的减少，，其晶体结构会发生明显的变化，正极材料的物相发生改变。随着锂离子含量的减少，材料的放电容量呈下降趋势，充放电电压平台逐渐清晰。Li1.15Mn2O4材料为层状-尖晶石型复合材料，即0.09Li2MnO3·0.91LiMn2O4，材料表现出良好的电化学性能，其结构中的Li2MnO3在充放电过程中能稳定尖晶石结构，使材料表现出良好的电化学稳定性。（2）通过研究镍离子对锰酸锂的影响可以发现，镍离子的加入会使尖晶石结构发生细微的变化，材料的晶格收缩。镍离子的掺入可以细化晶体颗粒大小，提高材料颗粒的均一性，进而减小了锂离子的扩散路径，提高其高倍率放电性能，但是较小的颗粒对循环性能影响较大。镍离子的加入能明显提高材料的放电电压，使材料具有较高的比功率。（3）通过研究钴离子对锰酸锂的影响可以发现，钴离子的掺入可以明显的改变晶体的微观形貌，使得晶体生长时按一定的方向优先生长。当钴的掺杂量达到0.1时，Li1.15Mn1.9Co0.1O4材料呈规则的正八面体，具有良好的电化学性能，钴离子的加入会对锰酸锂材料的容量有明显的损耗，但对其循环性能有一定的改善。在循环充放电过程中，Li1.15Mn1.9Co0.1O4的放电容量分为大致三个阶段，上升，保持，略微下降，晶体结构中钴离子的加入能提高材料结构的稳定性，使其在使用过程中表现出较稳定的电化学性能。
[Abstract]:Lithium-ion batteries are used as energy storage materials for mobile phones, cameras, laptops, electric vehicles and hybrid vehicles.Among them, the cathode material of lithium ion battery plays an important role in its structure.Because of its advantages of high working voltage, abundant raw materials, low price, good safety and environmental friendliness, manganese oxide cathode materials have been widely concerned, and have high application prospects in the market of power vehicles and so on.However, its application is limited due to its low specific capacity, capacity attenuation and poor cycle performance.It is an important method to improve the cycling performance of manganese lithium oxide material by doping lithium manganese oxide into solid solution by replacing manganese ion with cations.In this paper, lithium manganese oxide was modified by three kinds of cations by co-precipitation method.The crystal structure, apparent morphology and chemical composition of the material were characterized by X-ray diffractometer and scanning electron microscope (SEM), in order to analyze the change of crystal structure and the influence of the change of particle size and morphology on the properties of the material.In order to optimize the electrochemical performance of the material, the constant current charge-discharge test technique was used to determine and analyze the electrochemical performance of the material, and to explore the best doping amount of elements.1) by studying the effect of lithium ion on lithium manganese oxide, it can be found that with the decrease of lithium ion content, the crystal structure will change obviously and the phase of cathode material will change.With the decrease of lithium ion content, the discharge capacity of the material decreased, and the charging and discharging voltage platform became clear. Li1.15Mn2O4 was a layered spinel composite, that is, 0.09Li2MnO3 0.91 limn _ 2O _ 4, which showed good electrochemical properties.The Li2MnO3 in the structure can stabilize the spinel structure during charging and discharging, which makes the material exhibit good electrochemical stability.2) by studying the effect of nickel ion on lithium permanganate, it is found that the addition of nickel ion can make the spinel structure change slightly and the lattice shrink of the material.The addition of nickel ion can refine the size of crystal particles, improve the uniformity of material particles, reduce the diffusion path of lithium ion, and improve the discharge performance of lithium ion at high rate, but the smaller particles have a great effect on the cycling performance.The addition of nickel ion can obviously increase the discharge voltage of the material and make the material have higher specific power.3) by studying the effect of cobalt ion on lithium permanganate, it can be found that the doping of cobalt ion can obviously change the morphology of crystal and make the crystal grow in a certain direction.When the doping amount of cobalt is 0.1, Li1.15Mn1.9Co0.1O4 is a regular octahedron and has good electrochemical performance. The addition of cobalt ion will have obvious loss to the capacity of lithium manganese oxide, but it can improve its cycling performance to a certain extent.The discharge capacity of Li1.15Mn1.9Co0.1O4 is divided into three stages: rising, keeping and decreasing slightly. The addition of cobalt ion in crystal structure can improve the stability of the material structure.The results show that the electrochemical performance is stable in the process of application.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

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