Exploring The Modification Mechanism Of Electrode Materials For Lithium-ion Batteries: First-principles Calculations

The first-principles calculation method based on density functional theory is employed mainly to investigate the modification mechanism of two kinds of electrode materials for lithium-ion batteries, which characteristics could provide a research direction and the theoretical basement for continuous improvement in performance of lithium-ion batteries. The main content of this master thesis includes: The stability properties of native defects and zinc impurities in lithium titanate(Li₄Ti₅O₁₂) anode material and the associated effects on lithium-ion diffusion. The study of kinetic characteristics of lithium-ion diffusion in α-MnO₂·x H2 O cathode material.We report first-principles density functional theory studies the stability of native defects and zinc impurities in Li₄Ti₅O₁₂. The defects are characterized by their formation energies, electronic properties and geometrical structures. The Ti vacancy and the Li antisite as multiple acceptor defects in p-type samples are preferred under O-rich conditions, while the Ti interstitial and Ti antisite are energetically favorable under O-poor conditions. In Zn-doped LTO, substitutional Zn located at the 8a Li site is preferable to form under reducing condition, which brings a feasible decrease in TiO6 octahedral distortion and promotes the lithium-ion diffusion. For all native defects and Zn impurities,no localized states are found in the calculated band gap and their formation energies are all sensitive to the atomic chemical potentials and Fermi energy, which provide insights on how to design a rational defect-controlled synthesis condition to enhance the LTO’s electrochemical performance for targeted applications.The lithium-ion dynamic behaviors and performance of α-MnO₂·xH2O has been investigated by means of ab initio calculations. When there is no water molecules in theα-MnO₂ bulk crystal structure, which equals to x=0, the system shows antiferromagnetic configuration and the insulator properties. After the incorporation of 6.25 at% Li-ion,the spin degeneracy around the Fermi level is broken and shows magnetic ordering and half-metallic properties. However, 12.5 at% Li-intercalation α-MnO₂ result in the antiferromagnetic coupling again. When water molecules insert into the α-MnO₂（2×2）channels, they would get together by van der Waals force, stabilize the α-MnO₂ framework, improve the electronic conductivity and promote the lithium-ion diffusion. These characteristics bring many distinct advantages and reveal role of water molecules in the lithium storage process of α-MnO₂.