| The goal of this dissertation is to study the structure and performance relationship in cathodes material used in lithium-ion battery applications. In addition, functional materials used for other energy applications, such as oxygen reduction reaction in fuel cell and selective oxidation of ethane, are also discussed in the appendix.;Energy storage systems are the essential part for electric vehicles (EVs) and the urge for the development of affordable and reliable battery systems for EVs promotes the research on lithium ion battery. In this dissertation, two types of cathode materials, namely LixMo6S 8 Chevrel phase (CP) and nitrogen doped mesoporous carbon, were investigated, in the aim of developing high performance energy storage material, as well as establishing the correlation between the structures and high electrochemical performances.;Different from the traditional synthetic route, which requires high energy input and long calcination time, the LixMo6S8 Chevrel phase (CP) was synthesized via an one step molten salt method. Extraordinary electrochemical performance was observed and the Li+ transportation properties during discharge/charge process were also investigated. Electrochemical impedance spectroscopy (EIS) technique was used to characterize the transportation kinetics of Li ion insertion/extraction processes in the CP phase. X-ray diffraction (XRD) with energy dispersive X-ray (EDX) spectroscopy and scanning electron microscopy (SEM) were used to correlate the morphology change to the Li ion insertion process.;Nitrogen doped mesoporous carbon was developed as high performance cathode material for lithium-sulfur battery. Fundamental understanding of the mechanism of nitrogen promotion effect in mesoporous carbon was revealed by utilizing X-ray absorption near edge structure (XANES) spectroscopy to probe the chemical environment. With the existence of nitrogen dopant, the oxygen functional groups on the carbon surface were activated and tended to bond with sulfur species to form O-S bonds. This enhanced chemical adsorption process promoted the performance of Li-S battery in terms of cycling stability. |
