以硝酸銨-環六亞甲基四胺燃燒法合成奈米級LiMn2O4陰極材料製程研究; Nanocrystalline LiMn2O4 Derived by HMTA-Assisted Solution Combustion Synthesi

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Title:	以硝酸銨-環六亞甲基四胺燃燒法合成奈米級LiMn2O4陰極材料製程研究;Nanocrystalline LiMn2O4 Derived by HMTA-Assisted Solution Combustion Synthesi
Authors:	卓永達;Yung-Da Cho
Contributors:	化學工程與材料工程研究所
Keywords:	燃燒法;鋰錳氧;鋰離子電池;奈米材料;LiMn2O4;lithium-ion batteries;Nanocrystalline materials;combustion synthesis
Date:	2004-06-17
Issue Date:	2009-09-21 12:23:33 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本論文主要探討以燃燒合成法製備奈米級LiMn2O4陰極材料之製程研究，首先利用TG/DTA分析材料熱分解性質與相轉變反應，XRD鑑定各製程所得材料之結構變化，ICP-AES分析煆燒後鋰錳氧化物之計量比，SEM、TEM及BET鑑定合成材料之表面型態、顆粒粒徑與表面積，接著測試各材料之電池性能，進而求出最佳製程條件，並以循環伏安法分析材料氧化還原行為。本製程的合成變因有煆燒溫度、煆燒時間、鋰計量，及總金屬離子與燃料比例等。首先以硝酸鋰及硝酸錳為起始物，以硝酸銨(Ammonium nitrate)為製孔劑，環六亞甲基四胺(Hexamethylenetetramine)為燃料，改變不同煆燒溫度(500~900℃)與持溫時間(5~20小時)，探討最佳煆燒溫度與時間。接著，針對LixMn2-xO4中x為1.03進行研究。最後，改變不同金屬離子對燃料之莫爾比，分別為1比1、1比2與1比4等條件。本實驗最佳製程條件為煆燒溫度700℃，煆燒時間10小時，鋰計量x為1.00，總金屬離子對燃料之莫爾比例為1比1。上述合成條件下所得出的材料，在充放電速率0.1 C-rate及充放電截止電壓分別為4.3及3.0伏特時，其初次放電電容量為113 mAh/g，經過200個循環之後，其放電電容量為88mAh/g，電荷維持率為80%，雖其電容量不高，卻具有穩定之電池性能。由TG/DTA材料熱穩定性分析發現，當溫度於室溫與120℃間，產生第一段熱重損失，吾人認為是Mn(NO3)2?4H2O在溫度高於100℃時，發生分解與揮發，另外，在255℃有一熱解峰，此為LiNO3發生融化所造成。在溫度300℃以上，為反應主要熱重損失區。由XRD分析圖譜中可發現在煆燒溫度500℃以上之條件均可合成出尖晶石相產物。經由TEM鑑定結果，以總金屬離子與燃料之比例為1比1，於500℃下煆燒10小時所得LiMn2O4陰極材料，其顆粒粒徑約在25至40 nm之間，而於700℃下煆燒10小時所得之材料，其顆粒粒徑約在150至200 nm之間；由此可知，採用燃燒法可製備出奈米級且具優異循環穩定性之LiMn2O4陰極材料。 This dissertation covers the synthesis and lithium-intercalating properties of LiMn2O4 prepared by a combustion process with ammonium nitrate as a porogenic agent and Hexamethylenetetraamine (HMTA) as a fuel. The synthesis parameters, temperature and duration of calcination and lithium stoichiometry, as well as metal ion：fuel mole ratio, were optimized in order to obtain products with the best electrochemical activity. The phase transitions of the products were investigated by thermogravimetric and differential thermal analyses, Structural properties of the products were investigated by X-ray diffraction, surface morphology by scanning electron microscopy and transmission electron microscopy, and surface area by the BET method. Lithium intercalation properties were studied by galvanostatic charge-discharge studies for different rate windows. The various redox regions and phase changes occurring during the charge-discharge processes were studied by cyclic voltammetry. The precursors for the synthesis of LiMn2O4 were metal nitrates dissolved in an aqueous solution of ammonium nitrate and HMTA in various mole ratios of total metal ion to fuel and the products were obtained by calcination at different temperatures and times. The optimal synthesis conditions were found to be 10h calcination at 700°C with lithium stoichiometry and mole ratio of total metal ion to fuel at 1.00. At a 0.1 C rate between 3.0 and 4.3 V, the product gave a first-cycle discharge capacity of 113 mAh/g, which faded to 88 mAh/g in the 200th cycle, with charge retention of 80%. The weight loss that occurs in the range from room temperature to about 120°C is ascribed to superficial water loss, as well as water loss from the hydration of manganese nitrate tetrahydrate, which begins to decompose at temperatures above 100°C. The sharp endotherm at 255°C is due to the melting of LiNO3. The main decomposition and product formation begin around 300°C. All the diffractograms show patterns corresponding to the cubic spinel structure in the Fd3m space group, suggesting that LiMn2O4 was formed during the initial decomposition of the mixture at 500°C itself. The particles were crystalline and had an average particle size of 10 ~ 40 nm, and a BET surface area of about 3.0361 m2/g. The good electrochemical behavior of the product was attributed to the nanocrystalline LiMn2O4 cathode particles by a modified solution combustion process.
Appears in Collections:	[National Central University Department of Chemical & Materials Engineering] Electronic Thesis & Dissertation

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