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

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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.