Synchrotron X-ray Studies on Atomic and Electronic Structure of Matter: Li-ion Battery Cathode Materials

从日益流行的便携式电子产品（使用储存的化学能）到汽车（使用储存的化石燃料），便携式存储形式的能源对任何现代社会的重要性都可以很容易地理解。然而，对环境的影响和从燃烧化石燃料中获得的便携式能源的有限供应引起了人们对当前发展模式可持续性的担忧。另一方面，人们认识到清洁和可再生能源（太阳辐射、风和波浪等）在时间上是可变的，在空间上是扩散的，因此这些能源需要储存才能有效利用。锂离子电池技术已经主导了便携式电子设备的便携式存储能源供应，现在它面临着为高效的混合动力汽车和电动汽车供电的挑战。为了满足这一需求，需要更高能量密度的锂离子电池，为此，正极材料的重要性已得到广泛认识。在本研究中，我们建议研究正极材料Li2MSiO4 （M=Fe, Mn， Co或混合物）的结构特性，该材料的理论能量容量明显高于较发达或商业化的正极材料，如层状氧化物LiMO2 （M=Co, Mn， Ni或混合物），尖晶石氧化物LiM2O4 （M=Mn， Ni或混合物）和橄榄石磷酸盐LiFePO4。然而，要达到这一潜力，就意味着能够在保持纳米复合材料结构完整性的同时，从每个阳离子单元中可逆地提取/插入多个锂离子。设计纳米复合材料结构以克服一些基本的不稳定量子力学效应的挑战是提出研究的动机。在本研究中，我们的目标是对由正硅酸盐家族成员Li2MSiO4 （M=Fe， Mn或两者的混合物）制成的纳米复合材料的原子和电子结构的知识做出贡献，从而对此类纳米材料的电化学有基本的了解。我们将使用一套同步辐射技术来进行纳米材料的原位和非原位测量，并开发相关的分析方法来关联结构信息，如金属氧化态、位点配位和对称性、纳米晶相和相变序列、界面状态/结构，以提供对锂离子电池正极材料电化学行为的连贯理解。从拟议的研究中获得的结构信息对于合成化学家、纳米科学家和材料科学家制造下一代高能量密度可充电锂电池用于未来的电动汽车至关重要。**

The importance of energy in portable stored form to any modern society can be easily appreciated from the need for powering the ever increasingly popular portable electronics (using stored chemical energy) to automobiles (using stored fossil fuel). However, the environmental impact and the finite supply of the portable energy acquired from burning fossil fuels have caused concerns about the sustainability of the current development mode. On the other hand, it is recognized that the clean and renewable energy sources (solar radiation, wind, and waves etc.) are variable in time and diffuse in space, therefore these sources require energy storage for efficient usage. Lithium-ion battery technology has dominated the portable stored energy supply for portable electronics and now it faces the challenge for powering effective HEVs and EVs. Higher energy density lithium-ion battering will be needed to fullfil such need and to this end the importance of cathode material has been widely recognized. In this research we propose to study the structural properties of orthosilictes cathode material Li2MSiO4 (M=Fe, Mn, Co or mixture) which have a theoretical energy capacity significantly higher than that of the more developed or commercialized cathode materials such as the layered oxides LiMO2 (M=Co, Mn, Ni or mixture), spinel oxides LiM2O4 (M=Mn, Ni or mixture), and olivine phosphates LiFePO4. However to reach that potential means to be able to reversibly extract/insert more than one lithium ions from/into per cation unit while maintaining the nanocomposite structural integrity. The challenge of engineering the nanocomposite structure to overcome some of the fundamental destabilizing quantum mechanical effects is what motivates the proposed research. In the proposed research, we aim to contribute to the knowledge of atomic and electronic structure of nanocomposites made from members of the orthosilicate family, Li2MSiO4 (M=Fe, Mn or a mix of the two), for a fundamental understanding of the electrochemistry of such nanomaterials. We will be using a suite of synchrotron radiation techniques to carry out in situ and ex situ measurements of the nanomaterials and developing relevant analysis methods to correlate the structural information such as metal oxidation states, site coordination and symmetry, nanocrystalline phase and phase transition sequence, and interface states/structure to provide a coherent understanding of the electrochemistry behaviour of the lithium-ion battery cathode materials. Structural information to be acquired from the proposed research will be crucial to the synthesis chemists, nanoscientists and materials scientists to fabricate the next generation of high energy density rechargeable lithium-batteries for the electrical vehicles of the future.  **