鋰離子電池正極材料LiFePO4的製備與性能研究

Preparation and Property study of Cathode Material of Lithium-ion Battery - LiFePO4

朱晏誼(Yen-Yi Chu)

指導教授 ： 黃金花 ； 吳茂昆

國立清華大學/工學院/材料科學工程學系/碩士(2006年)

https://doi.org/10.6843/NTHU.2006.00419

摘要

鋰離子二次電池是以嵌入式的鋰化合物作為正、負極材料的新一代高能量蓄電池。近年來，鋰離子二次電池在各方面均不斷改進。相較之下正極材料的發展較為緩慢。在所有正極材料中，橄欖石結構的LiFePO4因具有安全性高、價格低、無環境污染、理論電容量較高等優點，被視為是下一代鋰離子電池最具有前途的正極材料。然而由於晶體結構的固有限制，LiFePO4具有極低的電子導電度與鋰離子擴散速率，這已成為限制其應用的最大障礙。
由於金屬離子摻雜是一種提高LiFePO4電化學性能很有前景的改性方法。然而，目前這方面的研究尚未深入，離子摻雜的類型也沒有更多的報導。因此在本實驗中，我們第一步先以溶膠-凝膠法合成材料，並對未摻雜的LiFePO4合成技術進行優化，第二步則以鈉離子摻雜拓展摻雜離子的種類，嘗試製備出電化學性能優良的LiFePO4，並對摻雜位置的不同與摻雜量進行比較。
實驗顯示，在導電碳含量為5~6wt％，且均勻包覆的條件下，LiFePO4以放電效率4C放電時，電容量保持在以0.1C放電時電容量的36％；當使用劑量比為摻雜5%的Na+於鐵位，合成後，相同放電效率下則保持了52%的電容量；而劑量比為1%的Na+摻雜於鋰位時，卻達到了與5%摻雜於鐵位相同的電化學性能。但使用劑量比為摻雜2%於鋰位、3%摻雜於鐵位所得到的結果，卻為所有摻雜樣品中電化學性能表現最差的樣品，也因此關於摻雜金屬離子仍需要更進一步的研究，以求達到實用的目的。

關鍵字

LiFePO4 ； 正極材料 ； 鋰離子電池 ； 摻雜金屬離子

並列摘要

Lithium iron phosphate (LiFePO4) has been a promising cathode material for Lithium ion batteries. Among the simplest, most widely studied and potentially most useful cathode material, much attention has been paid to it for its advantages, such as safety, environmental friendly, low material cost, high energy density, and very stable in common electrolyte systems. However, because of its lattice structure, it has extremely low electronic conductivity and very low lithium-ion diffusion coefficient, which has been the greatest obstacle for application of lithium iron phosphate.
In 2002, researchers show that by super-valence ion doping, , it does enhance the capacity delivery at high discharge rate. So that super-valence ion doping is an effective method to improve the electrochemical property of LiFePO4. However, few further research results were reported, and there are still lots of problems that needed to be solved.
In this paper, we first use sol-gel method to synthesize LiFePO4 and fine tune the synthesis process. Second we studied LiFePO4 based on Na+ doping. The result shows that the electrochemical performance after doping 1% Na+ doping at Li site is the same as 5% doping at Fe site. When using discharge rate at 4C, the capacity still maintain at 52% of discharge rate at 0.1C. There still need more researches to make improvement of electrochemical performance of LiFePO4.

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