以第一原理計算鋰嵌入與擴散於具氧空缺之二氧化鈦結構

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题名:	以第一原理計算鋰嵌入與擴散於具氧空缺之二氧化鈦結構
作者:	葉修良;Yeh, Hsiu-Liang
贡献者:	化學工程與材料工程學系
关键词:	第一原理計算;氧空缺;鋰嵌入;鋰擴散;二氧化鈦;First-Principles;Oxygen vacancy;Lithium intercalation;Lithium diffusion;Titanium dioxide
日期:	2018-06-27
上传时间:	2018-08-31 11:30:18 (UTC+8)
出版者:	國立中央大學
摘要:	二氧化鈦作為鋰離子負極材料研究於近年中獲得越來越多關注，其原因為二氧化鈦具有成本低、無毒性、質量輕並具備高理論電容量値。然而於實際應用面上，二氧化鈦卻時常受限於低電導率與有限的鋰離子擴散表現。先前的實驗團隊研究發現透過「氫化程序」處理二氧化鈦導入氧空缺於結構中可有效改善其作為鋰離子負極材料的表現性。本研究聚焦於三種常被作為鋰離子電池負極材料的二氧化鈦晶型：銳鈦礦、金紅石與單斜晶系二氧化鈦，基於密度泛涵理論以第一計算原理計算進行稀薄濃度狀態下，氧空缺對於鋰嵌入與擴散表現性影響。在三種晶相中，分別將鋰置於結構中潛在嵌入位置中以尋找其最穩定的嵌入位點。鋰於結構中擴散移動路徑則由其穩定嵌入位點至下一鄰近穩定位點以 CINEB(Climb Image Nudged Elastic Band)法計算而得。並採相同手法檢驗銳鈦礦、金紅石與單斜晶系二氧化鈦及其具氧空缺結構，以比較氧缺對於鋰在結構中嵌入與擴散行為的影響。此外，三種不同二氧化鈦及其具氧空缺結構之電子性質也進行計算分析。各項結果顯示在三種晶相中，單斜晶相二氧化鈦或許是最適合氫化程序產生氧空缺以作為鋰離子負極材料的選擇，因其結構導入氧空缺後鋰嵌入能最穩定且擴散能障上升幅度最低，電子結構分析上同樣觀察到帶隙下降的現象。;Titanium dioxide has recently attracted focus as a potential anode material in lithium-ion rechargeable batteries (LiBs) because of the low cost, abundant source, light weight, safety, and high theoretical capacitance. However, the practical application of TiO2 is restricted to its poor electronic conductivity and inefficient lithium diffusion. Previous studies show “hydrogenation processes” can remove the oxygen atoms from TiO2 and create oxygen vacancies, which may improve electronic conductivity and facilitate lithium mass transport to enhance anode material performances. In this work, three most common polymorphs of TiO2 as lithium-ion battery anode materials: anatase, rutile and TiO2(B) have been modeled and first-principles study based on density functional theory (DFT) calculations have been employed to investigate the intercalation and diffusion behavior of lithium in TiO2 with/without an oxygen vacancy at dilute lithium concentrations. Total energies of possible intercalation sites were first calculated to find out the favorable site among the three phases. Furthermore, all lithium diffusion pathways from one stable site to another stable site were examined by climbing image nudged elastic band method. To compare the effect of oxygen vacancy on lithium diffusion mechanism, energy barriers of pristine TiO2 and oxygen-defective structures have been calculated. In addition, the electronic structure of TiO2 with oxygen vacancy was calculated in comparison with pristine TiO2. The results indicate that among three polymorphs, TiO2(B) may the better choice for oxygen vacancy process because its intercalation energy is the most stable one, it has lower diffusion energy barrier change, and also show narrowed band gap after oxygen vacancy introduction.
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