published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The rechargeable lithium ion batteries (LIB) are playing increasingly important roles in powering portal commercial electronic devices. They are also the potential power sources of electric mobile vehicles. The first kind of the cathode materials, LiXCoO2, was commercialized by Sony Company in 1980s, and it is still widely used today in LIB. However, the high cost of cobalt source, its environmental unfriendliness and the safety issue of LiXCoO2 have hindered its widespread usage today. Searching for alternative cathode materials with low cost of the precursors, being environmentally benign and more stable in usage has become a hot topic in LIB research and development. In the first part of this study, lithium nickel manganese cobalt oxide (LiNi0.6Mn0.35Co0.05O2) is studied as the electrode. The materials are synthesized at high temperatures by solid state reaction method. The effect of synthesis temperature on the electrochemical performance is investigated, where characterizations by, for example, X-ray diffraction (XRD) and scanning electron microscopy (SEM), for particle size distribution, specific surface area, and charge-discharge property, are done over samples prepared at different conditions for comparison. The electrochemical tests of the rechargeable Li ion batteries using LiNi0.6Mn0.35Co0.05 cathode prepared at optimum conditions are carried out in various voltage ranges, at different discharge rates and at high temperature. In another set of experiments, the material is adopted as anode with lithium foil as the cathode, and its capacitance is tested. In the second part of this study, the iron based cathode material is investigated. Lithium iron orthosilicate with carbon coating is synthesized at 700℃ by solid state reaction, which is assisted by high energy ball milling. Characterizations are done for discharge capacities of the samples with different carbon weight ratio coatings. / published_or_final_version / Physics / Master / Master of Philosophy