| Description |
This thesis is aimed to develop high-capacity, inexpensive, long cycle life and environmentally benign anode for lithium-ion batteries. With those goals in mind, a novel oxide alloy composite materials MO-SnxCoyCz (MO=GeO2, SnO2, SiO and SiO2) have been proposed and investigated. Mechanical alloying method has been used to synthesize oxide alloy composite anode material. The MO-SnxCoyCz composite has the potential to combine the advantageous properties of both Sn-Co-C (long cycle life) and MO (high capacity) and, thereby, improve the overall electrochemical performance. The as-milled materials were studied by BET, laser particle analyzer, X-ray diffraction (XRD), scanning electron microscope (SEM), pair distribution function (PDF), extended X-ray absorption fine structure (EXAFS). Evaluating from electrochemical performance, tap density, and cost, GeO2 and SiO are the most promising candidates alloyed with Sn-Co-C system. The GeO2 composite anode shows a reversible capacity over 800 mAh/g with good capacity retention. Furthermore, the 1st cycle coulombic efficiency has been improved up to 80%. Compared with GeO2, SiO has an advantage on the price. A series of composite anode materials of xSiO • (1-x)SnxCoyCz were studied by electrochemical method. The composition of 50 wt.%SiO-50 wt.%Sn30Co30C40 shows the best electrochemical performance. Two different milling methods (ultra high-energy milling and SPEX milling) were employed to prepare the samples. Ultra high-energy milling sample exhibited superior electrochemical performance. Stabilized lithium metallic powder technique is employed on this anode to improve the first cycle coulombic efficiency. Full-cell configuration (Li1.2Ni0.15Co0.10Mn0.55O2 vs. 50 wt.%SiO-50 wt.% Sn30Co30C40) has been cycled over 200 cycles successfully. The SiO-SnxFeyCz (x : y: z molar ratio) composite has been milled in different compositions. Metallic iron was employed instead of cobalt, which cuts the cost significantly but does not sacrifice the performance in the meantime. The 50 wt.%SiO-50 wt.%Sn30Fe30C40 exhibited specific capacity of 900 mAh/g with acceptable cycle life. The electrodes were loaded with different current rates and showed excellent rate capability. Based on an overall consideration of various factors, SiO composite anode material prepared by ultra high-energy milling can provide the best electrochemical performance in terms of capacity and cycle life, and also have acceptable tap density and cost. |
