STRUCTURAL DESIGN OF HIGHLY ORIENTED LAYERED-MATERIAL FOR LITHIUM ION SECONDARY BATTERIES

锂离子二次电池以其重量轻、能量密度高、电压高等优点得到了广泛的研究，为了进一步降低成本和提高安全性，开发锂离子二次电池的正极和负极材料是至关重要的。对于阴极和阳极，一些层状化合物在比容量和循环性能方面具有吸引力。石墨通常用作阳极材料。氧化钒凝胶和氧化物青铜中的LiV_3O_8都是采用层状结构的正极材料，因而受到人们的关注。然而，它们的详细结构往往很难确定，因为它们的结晶颗粒的高度取向状态的倾向导致X射线衍射的信息差。因此，迄今为止，结构控制还不够。在本研究中，我们的目的是建立适合于高速率电化学反应的层状化合物的结构的基础上，它们的详细结构分析。这是准备应用于锂离子电池的电极材料。通过电化学方法制备了一系列不同锂含量的嵌锂石墨，并采用X射线衍射法对样品进行了垂直于石墨基面的c方向结构分析。对于一维结构的细化，高度取向的样品是足够的。然后，我们成功地确定了石墨烯层的堆叠方式，使用我们最初开发的一维Rietveld分析系统。我们可以讨论面内锂分布结构，以及c方向结构，这取决于锂嵌入水平。进一步研究发现，在电化学嵌锂和脱锂过程中，台阶结构的行为存在滞后性。这种滞后现象被认为与面内锂原子排列的结构变化密切相关。

Lithium secondary batteries have been widely investigated due to their advantageous characteristics of light-weight, high energy density, high voltage and so on. For further progress such as reduction of cost and improvement of safety, development of materials of cathode and anode is crucial. For both cathode and anode, some of layered compounds are attractive in terms of specific capacity and cyclability. Graphite are commonly served as anode materials. Vanadium oxide gel and LiV_3O_8, which is one of so-called oxide bronze, employ layer structure and draw attentions as cathode materials. Their detail structure, however, is often difficult to be determined on the grounds that tendency of highly oriented state of their crystalline particles causes poor information of X-ray diffraction. As a result, structural control has been not enough so far. In this study, our purpose was to establish the structure of layered compounds suitable for high rate electrochemical reaction on the basis of detail structural analysis of them. That is ready to be applied to the electrode materials of lithium ion batteries. We prepared electrochemically a series of lithium intercalated graphite with various lithium content and analyzed structurally in the direction (c-direction) perpendicular to basal planes by X-ray diffraction using highly oriented sample. For the one-dimensional structural refinement, the highly oriented sample was adequate. Then we successfully determined the stacking manner of graphene layers using our originally developed one-dimensional Rietveld analysis system. We could discuss in-plane lithium distribution structure, as well as c-direction structure, depending on lithium intercalation level. Furthermore we found that the behavior of stage structure was hysteretic between in the process of electrochemical lithium insertion and extraction. The hysteresis was considered to be closely related to the structural variation of in-plane lithium arrangement.