磷酸鋰鐵之磁性測量研究

Abstract

鋰電池由於其電容量大且可重覆使用的特性，在我們日常生活中的應用越來越廣泛，成為重要的儲電設備，而以磷酸鋰鐵做為鋰電池正極的材料，更成為下一代電池發展的主流。在磷酸鋰鐵材料的製作過程中，由於製備的方式不同會產生不同的雜質，而影響其製成電池後電性的表現。本研究希望透過磁性的測量來了解磷酸鋰鐵材料中的雜質及其電性的表現。我們測量了磷酸鋰鐵樣品中「磁化強度與磁場」的關係、「磁化強度與溫度」的關係及「磁滯曲線」等三種磁化曲線。發現帶有雜質的磷酸鋰鐵樣品其M-H磁化曲線在低磁場時具有陡升的線段，為磁赤鐵礦雜質的飽和磁化強度，而具有明顯磁滯迴圈的樣品，內含鐵磁序的Fe2P雜質。利用這些磁化曲線的特徵可以推測磷酸鋰鐵材料製成電池後電性的表現，做為初步檢測材料品質的工具。

Lithium-ion betteries which are used more widly in our daily life have been an important electric storage equipment because of its property of high energy density and reuse. LiFePO4 has been considered to be one of the most promising candidates for the next generation lithium ion batteries cathode materials. There are many different impurities in LiFePO4 with different methods for preparation. These impurities will affect the electric perfomance of Li-ion betteries. We hope to know how many impurities there are in our LiFePO4 samples and the influence of these impurities on the electric performance of Li-ion betteries. We analyzed the magentization curves, M(H), M(T), and hysteresis, of the LiFePO4 samples. We found steeply up lines at low fields in M(H) curves that shows the saturate magenitization of maghemite, and loops in hysteresis curves that shows the magnetism of Fe2P impurities which is ferromagnetic. We can use the characteristics of these curves to predict the electric performance of Li-ion betteries which use LiFePO4 as cathod materials. This mathod can be a tool to check the quality of LiFePO4 materials primarily.