2018年6月22日香港城市大学Qi Liu副教授学术报告

2018年6月22日香港城市大学Qi Liu副教授学术报告

报告主题：Discovery and Fundamental Studies of Phase Transformative Materials for Energy Application

报告人：Qi Liu副教授学术报告 香港城市大学

主持人：卢锡洪

时间：2018年6月22日15：00

地点：丰盛堂芙兰学术中心A403

欢迎广大师生参加！

报告摘要：

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, 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, I will briefly introduce how synchrotron-based techniques could be utilized for phase identification, fundamental study of structure dynamics, reaction mechanism, and doping mechanism.

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 and 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 a two-phase region. As the material continues to deintercalate and when appropriate 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 experience 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 to meet 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 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.

报告人简介：

Prof. Qi Liu currently work as an assistant professor at department of physics in City University of Hong Kong. He obtained his Ph.D. degree in Mechanical Engineering from Purdue University in 2014. After that, Dr. Liu performed his postdoc training at Argonne National Lab. His research has been focusing on “Fundamental investigation of phase transformative materials for energy application”. Through conducting a series of cutting-edge research, he have equipped himself with expertise in a large variety of synchrotron X-ray physics, materials synthesis and characterization techniques. Particularly, he is a leading expert in utilizing multiple synchrotron X-ray techniques for fundamental studies of materials in energy application. In addition, he has considerable experience in fabricating and testing prototype batteries. To date, He has already published 40+ journal articles including and given over 10+ international conferences.