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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/4136


    Title: 以融鹽法製備高振實密度之LiFePO4鋰離子電池陰極材料;High tap density LiFePO4/C cathode material by molten salt synthesis for Li-ion batteries
    Authors: 林逸全;Yi-Chuan Lin
    Contributors: 化學工程與材料工程研究所
    Keywords: 振實密度;融鹽法;磷酸亞鐵鋰;陰極材料;molten salt;Tap density;Cathode;LiFePO4
    Date: 2009-06-19
    Issue Date: 2009-09-21 12:32:04 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 本論文主要分為兩大部分,第一部分利用試藥級起始物,以融鹽法於不同煆燒溫度下合成出未經碳塗佈之磷酸亞鐵鋰粉體,再以行星式球磨機固定濕式研磨6小時減少粉體粒徑;最後將不同粒徑之磷酸亞鐵鋰粉末置於管狀高溫爐下游,而丙二酸碳源錠則置於管狀高溫爐上游,經由丙二酸生成的碳蒸鍍,於873 K煆燒12小時後,利用煆燒的過程,將碳塗佈於粉體表面,製備出不同粒徑大小之LiFePO4/C複合材料。 利用融鹽法於不同煆燒溫度下所合成的純磷酸亞體鋰粉體,皆有光滑的表面型態,而且隨著粉體平均粒徑的增加,其振實密度越大。另外,為了解材料中碳之塗佈情形,吾人以TEM/ SAED/ EDS進行分析,由EDS發現有些微的碳塗佈於LiFePO4材料表面,且以厚度5-10 nm之碳層薄膜包覆於灰黑色LiFePO4材料表面,經SAED分析後發現為不定型結構之碳。藉由一系列的材料特性與電化學性質鑑定分析,發現LiFePO4/C複合材料之粉體平均粒徑越小,其導電度、碳含量越高,電容量與長循環穩定性越佳,但材料之振實密度卻相對地較低。 由於第一部份所合成的磷酸亞鐵鋰/碳複合材料,其製程複雜與成本過高,將不利於商業化量產。因此,第二部分的製程開發主要著重在製程簡化與降低成本,而且為了提升材料的振實密度,吾人將結合碳熱還原法與融鹽法,利用兩製程的優點,合成出具備低成本與高振實密度之磷酸亞鐵鋰複合材料。第二部分採用工業級起始物,利用碳熱還原法合成出磷酸亞鐵鋰/碳複合材料,將其壓成錠後置於氧化鋁杯中,並且錠周圍以KCl包覆;最後再將氧化鋁杯置於管狀高溫爐中,於1028 K高溫下進行二次煆燒,使得原來的磷酸亞鐵鋰複合材料在KCl融鹽介質下,經過短時間的高溫反應,改變粉體的表面型態,使其趨於圓滑,並且增加粉體粒徑大小,提升材料之振實密度。 LiFePO4/C複合材料之粉體粒徑越大,其導電度越低,碳含量越少,導致有較差的電池性能。藉由拉曼光譜分析,分別經過KCl融鹽二次煆燒1.0與3.0小時之樣品,其ID/IG值有非常明顯的增加,由此可知KCl融鹽在煆燒的過程中,將會影響原有LiFePO4/C複合材料之表面碳層結構,導致石墨化碳之比例降低,降低LiFePO4/C複合材料之導電度。最佳製程條件之複合材料,其振實密度為1.50 g cm-3,於0.2 C電流速率與2.8-4.0 V截止電壓之電池測試條件下,初始放電電容量為139 mAh g-1,使其有最佳體積能量密度為212 mAh cm-3,經過323次充放電循環後,放電電容量為118 mAh g-1,電荷維持率達84 %。 Olivine-type cathode materials of LiFePO4 were prepared by a carbonthermal reduction method to lower synthesis cost. In order to enhance the powder’s tap density, the LiFePO4/C product was pressed into pellets and then sintered for at least 1 h at 755 ℃, which is the melting point of KCl salt. It is found that the molten salt can effectively influence the morphology and tap density of particles, and changes the electrochemical performance of the prepared LiFePO4. The compounds were characterized in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size distribution (PSD), and tap density testing. The final product with high tap density of 1.50 g cm-1 contained 4.58 wt.% carbon and exhibited excellent rate capability of 140.7 at the 0.2 C discharge rate between 2.8-4.0 V. The high tap density LiFePO4/C cathode material can be used in the lithium ion batteries to greatly increase their volumetric energy density.
    Appears in Collections:[化學工程與材料工程研究所] 博碩士論文

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