鋰離子電池目前受到越來越多的關注，因為它們可用於電子產品的主要電源，也是發展電動車的一大助力。鈦酸鋰(Li_4 Ti_5 O_12，LTO)，由於其安全性高、壽命長、成本低、對環境友善等特性，作為鋰離子電池的替代負極材料引起廣泛研究。然而，材料本身為絕緣體使得電導率低、且有低能量密度和產氣問題。此外，兩相之間(Li_4 Ti_5 O_12相和Li_7 Ti_5 O_12相)的界面以及LTO的表面結構和化學性質尚不完全清楚。本論文的目的是有系統地研究LTO的兩相界面，並提出提高LTO電導率的方法。本論文從對 LTO 特性的基本理解開始。發現摻雜是一種可以控制 LTO 電導率的直接方法。然而，摻雜是一個複雜的過程，因為摻雜和微觀結構之間的相互關係會影響整體電化學動力學特性，如電子電導率、顆粒尺寸的變化等。使用從頭算計算法(Ab initio calculation)，研究了各種 Cr 摻雜模型，並與未摻雜的 LTO 模型進行了比較。結果驗證了與未摻雜的 LTO 相比，Cr 摻雜的 LTO 的電導率增強。相變在鋰離子電池電極中起著至關重要的作用，對功率密度和循環壽命都是決定性的。透過目前的態密度研究，探索了界面處相變的動力學特性。提供了對Cr摻雜LTO和非摻雜LTO在充電和放電條件下界面處的運動和擴散勢壘的分析結果。
關鍵字: 從頭算計算法(Ab initio calculations), 〖鈦酸鋰(Li〗_4 Ti_5 O_12), 態密度(Density of States) ,鋰離子電池

Lithium-ion batteries (LIBs) have grabbed increasing attention because they are the dominant power sources for most portable electronics and the promising power sources for electric vehicles. Spinel lithium titanium, Li_4 Ti_5 O_12 (LTO) has attracted significant attention as an alternative anode material for LIBs due to its unique properties such as high safety, long life, low cost, and environmentally benignity. However, it shows an intrinsic insulator property, low energy density, and gassing issues. Moreover, the understanding interface between the two endmembers Li_4 Ti_5 O_12 phase and Li_7 Ti_5 O_12 phase and the surface structure and chemistry of LTO are not fully understood.
The aim of this thesis is to systematically study the interphase between the two endmembers of LTO and propose approaches to improve the electrical conductivity of the LTO. This thesis starts with the fundamental understandings of the bulk properties of LTO. Doping is found out to be a direct approach that can manipulate the electrical conductivity of LTO. However, doping can be a complicated procedure because of the interrelations between doping and microstructure which can influence the overall electrochemical kinetics properties like electronic conductivity, variations in the size of particles, etc. With the help of computational means like ab-initio calculations, various Cr-doping models were studied and were compared with the non-doped LTO models. The results verify the enhancements in the electrical conductivity of the Cr-doped LTO compared to the non-doped LTO, revealing the true doping effect.
Phase transitions play a crucial role in Li-ion battery electrodes being decisive for both the power density and cycle life. With the present DFT study, the kinetic properties of the phase transition at the interface were explored. The results provide an in-depth understanding of the phase boundary movement and the diffusion barrier at the interface during charging and discharging conditions for Cr-doped LTO and non-doped LTO.
Keywords: Ab initio calculations, Li_4 Ti_5 O_12, DFT, Lithium-ion battery.

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