中文摘要
  本研究室以溶膠凝膠法合成過量鋰陰極材料Li[Li0.2 Ni0.2 -Mn0.6]O2，測試其充放電特性，其第一圈電容量可達275mAh/g，並在循環充放二十圈後，能持續穩定放電在250mAh/g左右的電容量，本論文之主題在於提昇此材料之充放電速率能力及更佳的循環充放電特性，選由模版合成法合成柱狀結構陰極材料Li[Li0.2 Ni0.2Mn0.6] -O2，以期提高充放電速率能力，並配合以氧化鋯表面改質提高其循環充放電穩定性，比較溶膠凝膠法及共沈澱法所得材料之特性。此外，本論文亦針對另一過量鋰陰極材料Li[Li1/18Ni1/3Co1/6Mn4/9]O2，以臨場X光來觀察充電狀態時結構的變化，討論其各晶面位移或衰減的原因。
  於模版合成的部分，雖成功合成出層狀結構的陰極材料，但是其中僅以當表面自安定化改質2 mole% ZrO2 能保持原柱狀結構，未進行自安定化反應或反應物濃度僅1 mole% ZrO2的產物，其於燒結900oC後，皆已無柱狀結構，但2 mole%的相圖中，又呈現出明顯ZrO2自成一相，非我們所希望，僅覆蓋於陰極材料表面的情形，於充放電測之後，發現其電阻過而大，無法進行充放電，故其研究關鍵，就在於如何保持產物形狀又能不因為過多的金屬氧化物造成電阻上升。
  共沈澱合成法的過程中有些許製程問題的存在，故合成出有陽離子混合的產物，其反應在XRD圖上的即為層狀結構中I003與I104之間的比例不正確，以套裝軟體GSAS來精算材料中Li及Ni的混排情形，結果顯示出約有0.0862的Ni佔據了Li的3a層，而相對Li也有0.0862的莫耳比進入過渡金屬層中，其計量式建議為Li0.9183 -Ni0.0862[Li0.2862Ni0.1138Mn0.6]O2。
 Li[Li1/18Ni1/3Co1/6Mn4/9]O2於充電時，以臨場X光觀察其結構變化，發現鎳氧化同時伴隨鋰離子的遷出造成a軸的緊縮，c軸的拉伸，致使致使原有的晶面會有位移的現象，至於在鎳氧化時晶面的強度衰減，大多來自鋰離子遷出造成氧的負電荷相斥，而使過渡金屬與氧之間的鍵結改變，導致晶面的偏移或消失，而反應在XRD圖上鋒的減弱，而氧的流失造成材料中的氧缺陷，更使得所有晶面都受到影響，而導致鋒強度逐漸衰減。
  而在充電至高電位4.70V後，又出現另一電位平台，約在4.70-4.87V處，使晶格參數a、c軸皆上升，晶格體積增加，亦能提供約72 mAh/g的電容量，依估算此材料在4.70-4.87V時，鋰離子該以全數遷出，若考慮過渡金屬離子有遷出，則必發生嚴重相變化，但由本實驗所得之XRD相圖並無發現嚴重相變化，故推測此為電極與電解質之間的反應反應的方式與機制，仍須佐以其他研究加以驗證。

Abstract
The Li[Li(1-2x)/3MxMn(2-x)/3]O2 electrode materials emerged has a promising cathode for high energy density lithium-ion batteries. In this work, we have made an attempt to prepare Li[Li0.2Ni0.2Mn0.6]O2 compound of macro and nano-size powders by employing various preparative methods and then modified by coating with zirconium oxide. We have refined our observed results by crystallographic software to understand the changes in the super lattice structure and degree of cation mixing. We have also investigated the cobalt doped in Li[Li(1-2x)/3NixMn(2-x)/3]O2 compound during in-situ electrochemical cycling by synchrotron X-ray radiation.

The Li[Li(1-2x)/3NixMn(2-x)/3]O2 (x = 0.2) compound has been prepared by sol-gel, co-precipitation and template process. The resulted electrode powders/nanowires coated with zirconium oxide on its surface. The phase and surface morphology of the as prepared and modified electrode have been identified by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques, respectively. The single phase and layer structure have been found for all as prepared and except for the electrode coated with 1.0% of ZrO2 on the surface of the nano-wires obtained by template synthesis process. The integrated intensity ratio of (003) and (104) of Bragg’s reflections are used to determine the cation mixing and it is serious for the electrode materials prepared by co-precipitation method. The particle of micron in size and their distribution in the lattice has been identified from SEM micrographs. It is worth to mention that the nano-wire structure is maintained for the uncoated and coated electrode with 2% of ZrO2 and the results are consistent with that of the XRD analysis

The electrochemical cycle performance of the Li[Li0.2Ni0.2Mn0.6]O2 electrode prepared by sol-gel and co-precipitation has been performed in the potentials 2.5 – 4.7V at various current densities. The specific capacity of various electrodes is found to be comparable and the capacity fading is low for the modified electrode prepared by co-precipitation method. The variation in the specific capacity and the cycle performance of the as received and modified electrodes may be due to the change in phase and particle morphology as evidenced from XRD and SEM, respectively. Further, we have refined our XRD results using GSAS software to understand the super lattice reflections, the integrated intensity ratio of (003) and (104) and occupancy of cations to determine the degree of cation mixing (Ni and Li). The GSAS refinement results showed that the 43.1% and 8.62% of Ni and Li, respectively, occupied in the transition metal layer and the electrode composition is expected to be Li0.9183 Ni0.0862[Li0.2862Ni0.1138Mn0.6]O2.

In order to understand the changes in the structure of the Co-doped Li[Li(1/18)Ni1/3Co1/6Mn4/9]O2 compound, we have conducted in-situ XRD measurements at the charging process. The charging curves clearly showed two plateaus at the potential regions around 4.4 and 4.7 V and are attributed to the oxidation of nickel and loss of oxygen, respectively. The calculated lattice parameters a and c decreases and increases, respectively, in the first plateau (4.4V) region and increases in the second plateau region (4.7 V). The estimated capacity in the second plateau region is around 72 mAh/g . If we consider that this charge capacity is due to the contribution from the metal ions which will reflect on the Bragg’s reflection in the XRD pattern. Our in-situ XRD analysis did not revealed any changes in change in the peak position or phase. Therefore, the appearance of second plateau region capacity attributed to the result of side reactions that occurred during the electrochemical cycling and our results are consistent with the reported data in the literature.
The electrochemical results of the Li[Li0.2Ni0.2Mn0.6]O2 electrode suggests that the synthesis conditions need to optimized in order to maintain the nano-wire shape thereby lowering resistance on the surface of the electrode. The anomalous capacity of the Li[Li(1-2x)/3MxMn(2-x)/3]O2 (M = Ni and Co) electrode could be possible alternative to the LiCoO2 cathode for high energy density lithium-ion batteries.

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