以化學共沉澱法合成磷酸鐵應用於高功率磷酸鋰鐵陰極材料之研究

Synthesis of Iron Phosphate Spheres by Chemical Precipitation Route for High Power Lithium Iron Phosphate Cathodes

陳依伶(I-Ling Chen)

指導教授 ： 謝建德

元智大學/工程學院/先進能源碩士學位學程/碩士(2012年)

https://doi.org/10.6838/YZU.2012.00129

摘要

為因應全球能源需求，製備磷酸鋰鐵電池粉體以應用於高動力型鋰離子電池元件，是目前重要的課題之ㄧ。其遇到的瓶頸主要有導電性差和鋰離子擴散速率慢等。本研究利用碳熱還原法合成碳披覆之磷酸鐵鋰陰極材料，藉由物性分析和電化學測試，探討其應用於鋰離子正極材料之電化學特性。實驗主要分為二部份探討：(Ⅰ) 以共沉澱法製備FePO4‧xH2O前驅物，(Ⅱ) 利用碳熱還原法合成LiFePO4/C。第一部分以共沉澱法合成非晶態前驅物FePO4‧xH2O，其中pH值為一重要控制因子。實驗結果顯示當pH=3時，表面型態為分散均勻類球狀之形貌，其粒徑大小約為250 nm。第二部份利用碳熱還原法將前驅物搭配適量碳源，在氮氣氣氛下透過650oC煅燒，可成功合成LiFePO4/C粉體。由充放電循環測試發現，以pH=3合成之FePO4‧xH2O所製備之LiFePO4/C具有良好的電化學性能，其放電測試在0.1C及5C下分別為162.1和119.7 mAh g-1。造成LiFePO4/C電容量的提升及鋰離子具有高放電率，主要歸因於: (i) 類球狀之奈米級前驅物， (ii) 粉體表面均勻披覆薄碳層。此外，LiFePO4/C擁有良好之振實密度，其高達1.34 g cm-3，這能夠減少體積能量密度的損失，有效提升材料中可進行之充放電範圍，有助於LiFePO4/C陰極材料性能提升。

關鍵字

共沉澱法 ； 碳熱還原法 ； 磷酸鐵鋰 ； 鋰離子二次電池

並列摘要

Carbon-coated lithium iron phosphate (LiFePO4/C) composite has been synthesized by carbon thermal reduction technique. The physical characteristics and electrochemical properties of LiFePO4/C cathode material composite have been researched in this study. The aims of this study are divided into two parts: (Ⅰ) preparation of FePO4‧xH2O via co-precipitation, and (Ⅱ) synthesis of LiFePO4/C through carbon thermal reduction method. The main factor for preparing the LiFePO4/C composites is to start with the co-precipitation synthesis of FePO4‧xH2O spheres at pH = 3. The LiFePO4/C composite exhibits good crystallinity, well dispersed particle of 250 nm, and in situ carbon coating over the surface of LFP crystallites. The as-prepared LiFePO4/C composite delivers a high discharge capacity of 162.1 and 119.7 mAh g-1 at rates of 0.1 and 5 C, respectively. This enhanced rate capability is ascribed to the synergetic effect on the cathode that combines (i) quasi-spherical nanoparticles and (ii) thin carbon layer.with better discharge capacity at high discharge rate. Additionally, the LiFePO4/C composite presents a high tap density (1.34 g cm-3), inducing high performance without sacrificing the volume energy density. The result presented in this work show LiFePO4/C made from FePO4‧xH2O precursor synthesized under the condition that the solution at pH = 3 shows excellent electrochemical performance.

並列關鍵字

Co-precipitation ； carbon thermal reduction method ； Lithium iron phosphate (LiFePO4) ； Lithium ion battery

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