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Discovery and Fundamental Studies of Phase Transformative Materials for Energy Application

報告題目   Discovery and Fundamental Studies of Phase Transformative Materials for Energy Application
報告人   劉奇 博士
報告人單位   香港城市大學
報告時間   2019-08-22 15:00:00
報告地點   合肥微尺度物質科學國家研究中心一樓科技展廳
主辦單位   合肥微尺度物質科學國家研究中心


  Because of their high energy density, lithium ion batteries (LIBs) have become a rapidly growing energy storage technology, particularly in mobile applications, such as portable electronics, hybrid electric cars, etc. The cathode materials are considered to be the performance-limiting factor in research designed to increase cell energy and power density. During the cathode materials exploration, the advanced synchrotron-based characterization techniques, such as high-resolution synchrotron X-ray diffraction (HRXRD), in situ high-energy synchrotron X-ray diffraction (HEXRD), and in situ X-ray absorption spectroscopy (XAS), provide novel and powerful tools for exploring the structure evolution of battery materials. In my presentation, firstly I will briefly introduce how synchrotron-based techniques could be utilized for phase identification, fundamental study of structure dynamics, reaction mechanism, and doping mechanism during the cathode material exploration. Then, the presentation will be centered on the fundamental studies of V2O5 and LiCoO2 as the cathode materials for Li-ion batteries. Typically, the in-depth investigation of phase transformation behavior in V2O5-based and LiCoO2 in Li-ion batteries has been studied using advanced in situ synchrotron techniques. Take the LiCoO2 for example, theoretical and experimental investigations have shown that, when LiCoO2 is delithiated, the material will experience a series of phase transitions. Initially, there will be an insulator-metal transition in the low voltage region, resulting in a two-phase region. As the material continues to deintercalate and when approximately half of Li+ are removed from LCO, the material will experience an order-disorder transition, which drives the phase transition from the hexagonal structure to the monoclinic structure. Further delithiating LCO tends to induce the O3-O6(H1-3)-O1 phase transition process. Consequently, the unexpected phase transition and low Li+ diffusion at high voltage >4.3V prevent the lithium cobalt oxide from meeting the high-energy requirement. Here we develop a novel atomic-level multiple-element method to dope the LCO crystal structure with multiple elements. The resulting doped LiCoO2 (D-LCO) can withstand the increase in cell potential and still allow efficient lithium ion transport at high voltage, which exhibits extraordinary electrochemical performance: a high capacity of 190 mAh/g, approaching 70% of theoretical specific capacity of LiCoO2; a long cyclability (96% capacity retention over 50 cycles with a cut-off voltage of 4.5 V vs Li/Li+); and significantly enhanced rate capability. Such performance is the result of the combined effects of multiple doping elements on structural stability and lithium ion diffusion, which is supported via various electrochemical studies and synchrotron-based characterization. Especially, during the high voltage range, the O3-O6(H1-3)-O1 and order/disorder phase transition has been greatly suppressed.



  劉奇博士, 香港城市大學物理系助理教授, 于2014年12月畢業于普渡大學機械工程學院。2014.12~2018.3在美國阿貢國家實驗室先進光子光源部(APS)從事做博士后研究。目前主要致力于原位同步輻射技術在電化學反應、微波化學合成反應、材料合成、能量儲存和轉化等過程中原位檢測、反應機理和反應動力學研究方面的應用;已在物理、化學、材料和工程領域做出眾多原創性和突破性的工作。除了已經再包括Nature, Nature Energy, Nature Communications, JACS, Nano Letters, EES,  Nano Energy, Journal of Materials Chemistry, ACS Applied Materials Interface,  Electrochimica Acta 等國際知名期刊上發表高水平論文外,還作為第一負責人,搭建過國際上首臺原位同步輻射和化成技術的綜合測試平臺, 被美國能源部專家認為“為微波反應的機理研究提供了一個劃時代的研究手段”。其多項研究成果不僅得到了相關領域國際學術屆的廣泛認可和關注,也引起了工業界的廣泛興趣。


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