含有Fe2P及Li3PO4雜質之磷酸鋰鐵鋰離子電池正極材料之製備與特性

Preparation and characterization of LiFePO4 cathode materials with impurities of Fe2P and Li3PO4

許哲彰(Je-Jang Shiu)

指導教授 ： 吳溪煌

大同大學/工程學院/材料工程學系所/碩士(2010年)

摘要

本研究利用溶液法合成橄欖石結構之計量比LiFePO4於不同溫度下熱處理以及利用鐵含量少於計量比之LiFe1-xPO4 (0 ≤ x ≤ 0.09)之正極材料。利用XRD, ICP-OES, EA, SEM分析合成樣品之晶體結構、成分組成、碳含量與表面型態等等。合成樣品之電化學分析方面利用循環充放電測試來分析電容量衰退、循環伏安分析來探討氧化還原反應之可逆性。由XRD結果來看,經由800oC以上熱處理之LiFePO4生成Fe2P, 但並未如同參考文獻當中改善循環表現及降低衰退,相對的在775oC熱處理之樣品擁有較好之循環表現,850oC以上熱處理出現Li3PO4也造成電容量的減少。經由SEM觀測可發現顆粒尺寸隨熱處理溫度升高而變大,是導致電化學特性表現不佳的因素之ㄧ。近一步藉由循環伏安之測試發現Fe2P之生成有助於提升鋰離子傳導係數。 LiFe1-xPO4 (0 ≤ x ≤ 0.09)之測試發現在鐵少3%至5%左右有較好之循環表現。

關鍵字

LiFePO4 ； Fe2P ； Li3PO4

並列摘要

In this study, a solution method was used to prepare stoichiometric olivine structured LiFePO4 at various heat treatment temperatures and LiFe1-xPO4 (0≤ x ≤ 0.09) cathode materials. The crystalline structures, compositions, carbon contents, and morphology of the synthesized samples were investigated with XRD, ICP-OES, PSA, EA, and SEM. The electrochemical properties of synthesized samples were analyzed by capacity retention and cyclic voltammetric studies. From the results of XRD, Fe2P was found in samples heat-treated at temperatures higher than 800oC. However, it does not improve the cycling performance and rate capability in comparison with the sample prepared at 775oC which shows the best cycling performance among the prepared samples. Whereas the samples prepared at temperatures higher than 850oC show significant capacity fading that might be attributed to the existence of Li3PO4 impurity and particle size growth. From the diffusivity of Li+ ions in the prepared samples determined from the results of cyclic voltammetric study with various potential scan rates, the existence of Fe2P can increase the diffusion coefficient of lithium ion. Among the prepared LiFe1-xPO4 (0 ≤ x ≤ 0.09) samples, powders prepared with 0.03 ≤ x ≤ 0.05 show better cycling performance than others.

並列關鍵字

LiFePO4 ； Fe2P ； Li3PO4

參考文獻

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