本論文主要分成兩部分，第一部分以氧化鋯表面修飾商品化之LiCoO2，並探討氧化鋯塗層對LiCoO2電池性能增進之機制。分別以、交流阻抗分析、及臨場X光繞射分析，來討論LiCoO2陰極材料於充放電時，其鈷溶解、內部極化現象與結構之變化，以深入了解以表面修飾後，增進其電池性能之原因。
 於實驗中，以0.5 mole%之氧化鋯表面修飾於LiCoO2陰極材料表面上，由穿透式電子顯微鏡可發現在陰極表面上覆蓋一層約40~ 60 nm之氧化鋯。而在鈕扣型電池充放電測試中，於高充電電壓、與高充放電速率時，經表面修飾之LiCoO2皆有較好之性能表現。而在探討電解液之影響，氧化鋯能有效阻隔陰極材料與電解液之接觸，抑制鈷與鈉離子嵌入陰極材料內，造成不可逆電容量的產生。於交流阻抗測試可知，經三十圈充放電循環測試後，表面修飾之LiCoO2能抑制陰極材料本身與電荷轉移之阻抗的增加，使其內部極化現象較小，而能有較好之電池性能。最後在臨場X光繞射分析方面，於第一圈充電狀態時；在高電壓時，可以發現表面修飾之陰極材料，能減緩其結構晶格參數之變化，穩定其結構。相對於未改質之陰極材料，於4.5V時，其結構因大量鋰離子遷出，而造成晶格常數的變化，而此證明經表面修飾後之LiCoO2，能在高電壓下抑制其結構之崩壞，使其在放電時，仍有較高之放電電容量，和較低之不可逆電容量。因此，在增進電池性能的機制中，鈷溶解、陽離子混合效應、結構的穩定性及阻隔與電解液之反應皆扮演一重要之角色。
第二部分則是繼本研究室研究結果，Li[Li(1-3x)/2NixMn2/3-x/3]O2 這系列組成的陰極材料擁有較高的電容量，由以x=0.2時為一最佳組成，但是也因為這系列的材料於快速率充放電能力不佳的關係，所以將相同以0.1、0.2 mole% ZrO2用來表面修飾Li[Li0.2Ni0.2Mn0.6]O2陰極材料，使其能有更好之電池穩定性和快速充放電之能力。經實驗結果顯示，於速率為10 mA/g，以四十圈循環充放電測試後，以0.2 mole% ZrO2表面修飾之陰極材料，其衰退率只有1.7%，優於未改質與0.1 mole%的5.1%、5%。證實經ZrO2表面修飾之Li[Li0.2Ni0.2Mn0.6]O2陰極材料，亦仍增進其充放電性能。

The study was divided two parts. The first part was to discuss the effect of the zirconia coating on LiCoO2 to the performances of cathode materials in lithium batteries. The mechanism for improving the charging potential and charging- discharging rate of the zirconia-coated LiCoO2 were investigated. For the purpose, in-situ X-ray diffraction analysis of the synthesized zirconia- coated LiCoO2 was studied to realize the variation of the unit cell during charging-discharging process. Further, AC impedance spectroscopy of the synthesized materials was investigated at different charging states to observe the function of the surfaced zirconia to impedance distribution of the batteries. The electrolyte composition was also modified for examining the dissolution of cobalt during charging-discharging process.
From TEM analysis, it was clearly shown that one thin layer of 0.5 mole% zirconia-coated LiCoO2 with a thickness about 40-60 nm. The charging-discharging tests of the zirconia-coated LiCoO2 revealed better capacity retention at high C-rate and high charging potential. For the study of the cobalt dissolution by the modified electrolyte, the surfaced zirconia was capable to insulate the electrolyte from LiCoO2. Therefore, the cobalt and sodium ions intercalated into LiCoO2 were not possible. From AC impedance analysis, the zirconia-coated LiCoO2 showed better restriction to increase of bulk resistance and charge transfer resistance. Thus, better cell performance was revealed. Finally for in-situ X-ray diffraction analysis, the change in the cell parameters of the zirconia- coated LiCoO2 was decreased when comparing with that of bare LiCoO2 charged to 4.5V. The decrease in the parameter variation of the zirconia-coated LiCoO2 unit cell showed strong evidence to restrict the crystalline structure collapse when charging to higher potential. Thus, the materials exhibited higher discharging capacity and lower irreversible capacity.
The second part dealt with the studies on the zirconia-coated Li[Li(1-3x)/2NixMn2/3-x/3]O2. In the previous results from our lab., materials with x=0.2 showed the highest capacity, however, the poor conductivity made itself difficult to cycle at higher C-rate. Thus, in this study, the synthesized Li[Li(1-3x)/2NixMn2/3-x/3]O2 was coated respectively by 0.1 mole% and 0.2 mole% zirconia to improve the stability and ability of high C-rate cycling. It revealed that the 0.2 mole% zirconia-coated Li[Li(1-3x)/2NixMn2/3-x/3]O2 showed better capacity retention after 40 cycles with charging-discharging rate of 10 mAg-1. The capacity loss was merely 1.7% where that of 0.1 mole% zirconia-coated and bare Li[Li(1-3x)/2NixMn2/3-x/3]O2 were 5.1% and 5.0%, respectively. It also indicated the surfaced zirconia did improve the performance of Li[Li(1-3x)/2NixMn2/3-x/3]O2.

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