【作者】 宁连才；

【导师】 吴金平； 程寒松；

【作者基本信息】 中国地质大学 ， 应用化学， 2006， 硕士

【摘要】 锂离子电池具有比能量高、功率大、使用寿命长、安全性能好等优点，在手机、摄像机、笔记本电脑等便携式设备中已得到了广泛应用，在电动车领域也展示出了良好的应用前景，日益受到广泛关注。1990年Sony公司使以钴酸锂为正极材料的二次锂离子电池实现了商品化，但由于钴资源短缺、价格偏高、有毒而限制其推广使用。相比之下，锰酸锂（LiMn₂O₄）由于资源丰富、价廉、环境友好等优点，使其成为最有希望取代钴酸锂的正极材料。但锰酸锂的放电容量相对较低，结构欠稳定，作为正极材料还无法与钴酸锂相比。为改善锰酸锂的电化学性能，国内外科研工作者进行了大量的实验研究，众多实验方法的尝试使实验消耗了大量的时间、人力、物力和财力。 近年来，随着计算机软硬件的发展，几乎所有的化学性质都可以用定性或近似定量的计算形式来描述。对锰酸锂正极材料采用合适的理论方法进行计算，其计算结果能够解释实验现象和预测材料性能，揭示出一些普遍性规律，因而可以指导实验制备，这种研究方式已经引起研究者的广泛重视。本文采用第一原理密度泛函理论中的广义梯度近似法，对尖晶石型LiMn₂O₄进行了理论计算，从电子结构上探讨了锂在嵌入正极材料后的存在形式，以及锂离子嵌入后对电极材料性能的影响，研究了掺杂离子对锂离子电池循环性能和容量的影响，同时从电子结构的角度提出了掺杂抑制Jahn-Teller效应的指纹，并解释了掺杂抑制Jahn-Teller效应的机理。 本文首先对锂在锂锰氧化物中的嵌入／脱出结构模型进行了理论研究，分析了不同量的锂嵌入到LiMn₂O₄中的结构变化并计算了相应的形成能，预测了锂嵌入到LiMn₂O₄中的嵌入电压，同时给出了不同的锂嵌入量情况下体系的电子态密度和各元素的净电荷等性质。计算后发现，锂嵌入的平均形成能为-4.46eV，锂嵌入后体积的总变化为5.71％，平均嵌入电压为4.90V。电子态密度分析表明，Li⁺是相对独立的，可以在锰离子和氧离子相互作用形成的骨架中近似自由地嵌入／脱出，锂的嵌入使电子跃迁的能隙减小，材料的导电性大大增强。净电荷分析表明，氧原子和锰原子之间成键的共价性强，而离子性弱，Li嵌入后的离子化程度较高，并且锂失去的电子大部分都转移给O，而Mn获得的电子较少。这一理论计算结果对尖晶石型LiMn₂O₄的设计和性能改进有一定的参考价值。 在充分了解了锂锰氧化物的性质后，本文进一步研究了过渡金属Ti、Cr、Fe、Co、Ni、Cu、Zn掺杂对尖晶石型LiMn₂O₄的电子结构及放电平台的升高机理。分析认为由于M-3d能带的诱导作用，出现新的O-2p能带。当过渡金属M由Ti变化到Zn时，M-3d能带逐渐向低能量的方向移动，新的O-2p能带出现的位置也随之下移。当Li脱出时，将需要更多的能量才能从新的O-2p能带上获得电子，体系就能够获得更高的嵌入电压，可见，这种高更多还原

【Abstract】 Lithium ion batteries are advantageous for their high energy density, high power density, long calendar life and better safety. It has been widely used in portable electronic devices and the prospect for future applications in electric vehicles, hybrid vehicles and stationary power generation, and thus was actively studied in recent years. The very first commercial application of LiCoO₂ cathode materials in rechargeable batteries was reported in 1990. Unfortunately, applications based on LiCoO₂ materials have been limited only to portable electronic devices due to lack of sufficient cobalt resources and the toxicity of these compounds. It is therefore highly desirable to develop lower cost, more environmentally friendly materials with richer natural resources. A large number of novel cathode materials alternative to LiCoO₂ have been proposed and actively pursued. Among them, the spinel type lithium manganese oxide LiMn₂O₄ presents a promising candidate for serving as a novel cathode material. With great manganese abundance in nature, lithium manganese oxide compounds can be made quite inexpensively. Unfortunately, lithium manganese oxide possesses the drawback of low discharge capacity and unstable structure upon applications in lithium-ion batteries, particularly at a higher temperature, as observed in many experiments. Thus, a large number of experiments have been undertaken to improve its electrochemical properties. Large amounts of manpower and material resources were taken away since there are too many experimental methods.In recent years, with the development of computer hardware and software, we can now predict almost all the chemistry properties semi-quantitatively or even quantitatively via computer simulation. Currently, theoretical calculations performed on spinel manganese cathode materials can not only interpret experimental results but also predict the performance of novel materials. The general principles formulated from them can then be used to guide the synthesis in experiments. In this paper, we calculate the spinel LiMn₂O₄ system using first principles studies based on density functional theory under general gradient approximation. We discussed the material properties and the status of lithium atom after the Lithium insertion by electronic structure analysis, as well as the effect of dopping to cyclic life and capacity of lithium ion battery. Furthermore, we present a criterion of Jahn-Teller effect, and explain the mechanism why dopping can restrain this distortion.We attempt to address several key issues concerning the structural variation, the energetics, the更多还原