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系統識別號 U0026-1307201413182700
論文名稱(中文) 第一原理討論摻雜後陰極材料磷酸鋰鐵的材料性質變化
論文名稱(英文) Effects of metal doping on the material properties of LiFePO4 cathode material by first-principle calculation
校院名稱 成功大學
系所名稱(中) 機械工程學系
系所名稱(英) Department of Mechanical Engineering
學年度 102
學期 2
出版年 103
研究生(中文) 林瑞桓
研究生(英文) Ruei-Huan Lin
學號 n16014386
學位類別 碩士
語文別 中文
論文頁數 78頁
口試委員 指導教授-陳鐵城
口試委員-屈子正
口試委員-林震銘
口試委員-方得華
中文關鍵字 鋰離子電池  金屬摻雜  磷酸鋰鐵  能隙  鋰離子擴散 
英文關鍵字 lithium-ion batteries  metal doping  LiFePO4  band gap  diffusion 
學科別分類
中文摘要 近年來,具有規則橄欖石結構的LiFePO4被視為非常具有發展潛力的鋰離子電池陰極材料,LiFePO4具有高工作電壓、成本低、無汙染等諸多優點,但是LiFePO4電子導電性不佳及鋰離子擴散係數低的缺點限制LiFePO4的應用,摻雜金屬離子是一種有效改善材料性質的方法,本研究以第一原理為理論基礎,討論摻雜金屬離子後LiFePO4的材料性質變化。
本研究利用VASP量子化學計算軟體模擬摻雜金屬離子後LiFePO4的材料性質變化,模擬結果顯示,摻雜金屬離子可有效的抑制鋰離子在脫嵌過程中產生的體積變化,有助於提升材料的使用壽命。鋰離子的擴散與晶格的間隙有關,量測摻雜金屬離子後的晶格間隙皆呈現變大的趨勢,代表摻雜金屬離子可提升鋰離子的擴散速率。由能隙結構圖發現摻雜金屬離子可縮小LiFePO4的能隙大小,表示摻雜金屬離子可有效的提升LiFePO4的導電性質,由電子狀態密度圖發現能隙縮小的主因,在於摻雜的金屬離子在費米能附近有局域性的電子分佈,使價電帶與導電帶電子的能量差距縮小,其中以摻雜V離子的改善效果最佳,能隙約為0.2068 eV遠小於未摻雜LiFePO4的能隙(0.9245 eV)。
英文摘要 In the recent years, LiFePO4 materials with the olivine structure have become a promising cathode material for the lithium ion battery. LiFePO4 has a lot of advantage, such as high operation voltage, long operational life, low materials cost, environmental friendliness. However, disadvantage of low electronic conductivity and poor ionic conductivity greatly restricts the commercial applications of LiFePO4. Metal doping is one of the effective way to improve materials properties of the LiFePO4. In this study, the materials properties of LiFePO4 after doping metal ions were performed by first-principles calculation. It was found that doping metal atoms to LiFePO4 can significantly reduce the volume variation during the lithiation/ delithiation cycles. Consequently, the working life of cathode materials can be improved. The metal doping in LiFePO4 leads to the increase of hopping distance. This expansion effect would benefit the Li ion diffusion. The effects of metal doping on the electronic structures were performed by the investigation of band structure. The results show that doping metal ion into LiFePO4 induces a narrowing of the band gap, which could benefit to improve the electronic conductivity. From the analysis of the density of states, we can find the energy bands near the Fermi energy were mainly attributed to the doping metal atom. This result leads to the decrease of energy gap between the valence band and conduction band. In this work, V-ion doping shows an optimum effect than other elements under study. The band gap of V-ion doping (0.2068eV) is much smaller than the band gap of un-doped LiFePO4 (0.9245eV).
論文目次 目錄
摘要 I
誌謝 VI
目錄 VII
表目錄 X
圖目錄 XI
第一章 緒論 1
第二章 文獻回顧 10
2.1磷酸鋰鐵(LiFePO4)簡介 10
2.2 LiFePO4電化學性質的改善方法 16
2.2.1表面塗佈層改質 16
2.2.2摻雜金屬離子改質 21
2.2.3控制材料粒子大小及形態改善電化學性質 24
2.3 LiFePO4的製備方法 25
第三章 基本理論 29
3.1薛丁格方程式 30
3.2多電子系統的薛丁格方程式 31
3.3 Born-Oppenheimer近似 32
3.4 Thomas-Fermi模型 34
3.5 Hohenberg-Kohn方法 34
3.6 Kohn-Sham方法 35
3.7局域密度近似法 37
3.8局域自旋密度近似法 38
3.9廣義梯度近似法 39
3.10布洛赫定理 40
3.11能帶理論 41
3.12自洽方程式 42
3.13贗勢法 43
第四章 結果與討論 45
4.1模擬計算參數 45
4.1.1計算細節 46
4.1.2計算模型 46
4.2 LiFePO4的材料性質 48
4.2.1摻雜金屬離子前後LiFePO4的晶格結構 48
4.2.2摻雜金屬離子後LiFePO4的擴散性能變化 55
4.3 LiFePO4的電化學性質 58
4.3.1摻雜金屬離子後LiFePO4的電化學性質 61
4.3.2摻雜多種金屬離子後LiFePO4的電化學性質 69
第五章 結論與未來展望 72
5.1結論 72
5.2未來展望 74
參考文獻 75
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