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

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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.  **