二次锂离子电池用电极材料中离子输运与存储机制的同步辐射研究

The success of rechargeable lithium ion batteries used in portable electronics makes them highly expected as the promising candidate for propulsion and storage batteries in automotive and electric grid. However, to meet these application demands, it requires to greatly improve their energy density and power density without sacrifice of safety, cost and environmental friend. It is known that the battery performance is determined by the ion transport and storage properties in the electrode materials. Therefore, it is very essential to deeply understand the fundamental scientific issues related to the key factors limiting the development of high-performance electrode materials. In recent years, synchrotron X-ray techniques become more important for investigating basic issues in lithium ion batteries because of their distinctive advantages. Based on such recent research progress and high demanding for improvement of battery performance, this project is going to carry out the basic study of high-performance electrodes by using X-ray diffraction (XRD) and absorption fine structure (XAFS) techniques in Shanghai Synchrotron Radiation Facility. It is aiming to obtain information on evolution of lattice constant, chemical composition, elemental bond valence and atomic occupation during processes of lithium ion insertion and extraction, elucidate the crucial as well as general mechanism of ion transport and storage, disclose the limiting factors for great improvement of lithium storage capacity and fast transport, eventually providing useful information for construction of high-performance rechargeable lithium ion batteries.

二次锂离子电池应用于便携式电子产品所取得的成功，使人们对它在动力和储能电池方面寄予了更高的期望。但是怎样在保证安全、成本及环境友好的前提下，提高电池的能量密度和功率密度以满足以上两方面应用的要求一直是急需解决的问题。电池的性能归根结底取决于电极材料中锂离子的输运和存储特性，深入理解影响离子输运和存储的关键因素是提高电池性能的先决条件。同步辐射X射线技术由于其显著的优势，近年来成为这方面研究的重要手段。本项目即是依据锂离子电池发展的需求及其同步辐射研究的最新发展动态提出的。拟依托上海光源，针对高性能的电极材料，开展X射线衍射与吸收谱的研究。探明锂离子反复脱嵌过程中材料的晶格常数、物相组成、元素键价及原子占位的变化规律，阐明离子输运与存储过程中的关键共性科学机制，揭示制约储锂容量和锂离子迁移率提高的关键因素，为高性能二次锂离子电池的构筑提供有益的信息。

锂离子电池在便携式电子产品、动力和储能电池应用中都发挥重要作用。为了满足当前动力和储能电池的要求，现有锂离子电池需要在保证安全、成本、环境友好的前提下，提高能量密度、功率密度以及循环稳定性。这些性能的本质上取决于电极材料及电极电解质间界面的物理结构和化学状态，其中涉及到构成物质的形态，反复充放电过程中不同组成部分之间的相互作用，以及微观的动态的电荷转移、体相材料和界面间载流子电荷和质量输运、结构相变。澄清这些物理化学特性的演变，阐明影响离子输运和存储的关键因素是实现电池性能提高的先决条件；建立原子分子水平的瞬态物理化学过程与宏观性能之间的联系，才能从源头上获得材料性能提高的解决方案。同步辐射X射线作为研究锂离子电池充放电过程中物理化学特性演变的有力手段收到该领域的高度重视，是推动锂离子电池材料的研发的有力工具。.工作依托上海同步辐射光源，与BL14W1、BL14B1、BL08U、BL15U等线站的研究人员合作，针对高容量正极材料锰基富锂层状固溶体、锂氧气高容量正极材料、纳米负极TiO2、负极材料Li4Ti5O12及VN、固体电解质锂镧锆氧材料开展了研究。揭示了以上材料在充放电过程中元素价态及局域结构的演变，阐明.电子转移与局域结构演变对容量和电压衰减的影响机制，澄清界面储锂的微观作用机制，发现并确定锂氧反应产物的物相结构以及固体电解质材料晶界中存在的第二相结构。所得到的结论为深入理解锂电池各组成部分材料的工作和制备机理提供了实验依据，为提高电池性能提供了方向性指导。同时，也为采用同步辐射技术研究锂电池开拓了方法手段。