| The main content of this thesis includes:study on the lithium ion dynamic properties for Solid electrolyte interphase; the investigation on mechanism of lithium ion diffusion in Li4+xTi5O12 anode material; the research of ion dynamic behavior in Li2MnO3 cathode materialFirstly, three important inorganic components(Li2CO3,Li2O, LiF) in Solid electrolyte interphase have been investigated comprehensively. Using density functional theory, the electronic structures of the three compounds are calculated and lithium migration dynamics are simulated using nudged elastic band method. Results show that all three components have insulating electronic structures, while lithium vacancies create some strongly localized holes that do not contribute much to the electronic conduction. Lithium diffusion in LiCO3 and Li2O can be very fast with the help of vacancies when lithium vacancies are available. The energy barriers of lithium migration in LiCO3(ranges from 0.227 to 0.491eV) and Li2O (0.152eV) are comparable to that in graphite. However, lithium migration in LiF (energy barrier 0.729eV) is much slower even when there are lithium vacancies in the lattice. Therefore, we can manually improve the lithium diffusivity by decrease the amount of LiF in the Solid electrolyte interphase.Secondly, the structure of Li4+xTi5O12 and the mechanism of lithium ion diffusion have been studied systematically. Large 1×1×3 supercell models are constructed and used to calculate the total energy and electronic structure. The calculated electronic structures have shown that the delithiated state Li4Ti5O12 insulating while the lithiated state Li7Ti5O12 is metallic. The metallic characteristic of the electronic structure shows that the electronic conductivity of Li7Ti5O12 is much higher than that of the insulating Li4Ti5O12, which is in agreement with the experimental observations. Furthermore, The diffusion pathways are optimized and the energy barriers of lithium migration under four types of dilute defect extremes:Li4+δTi5O12,Li4-δTi5O12, Li7+δTi5O12 (δ＜＜1)are calculated with the nudged elastic band method. Results show that lithium diffusion in the charged state(energy bartiers are 1.0 and O.7 eV for interstitial Li and Li vacancy dififusion,respectively)is much slower than in the discbarged state(energy barriers are 0.13 and 0.35 eV for interstitial Li and Li vacancy diffusion,respectively).The diffusion coefficients are also evaluated based on lattice gas model and hopping mechanism. The obtained results are compared with availab le experimental data within a two-phase co-exiscence framework. The theoretically evaluated diffusion coefficient is qualitatively in good agreements with the available experimental findings.Third, the Li-ion storage mechanism of the layered Li2MnO3 has been investigated as cathode macerial for lithiam ion battery The electronic structures, intercalation potentials and lithium ion dynamic behaviors are calculated by means of density functional theory Results show that the energetically most favorable ground state is antiferromagnetic in layered Li2MnO3,and the electronic strueture of Li2MnO3 compound is predicted to be insulating Within the GGA+U approach,the calculated mtercahtion voltage(ranges from 4.5V to 4.9V)is found to be in good agreement wich experiments.Upon lithium removal, seriotts structural deformation occurs and some of the oxygen atoms move close and bond to each other gradually in the lattice when most of the lithium atores are removed.Further analysis of density of states shown that those oxygen atoms losses charge and appearing as(O2)2--states,in agreemerlt with recent experimental observations.Lithium diffusion in bulk(Li2MnO3 is also studied.Unlike the two dimensiorlal diflusion pathways in rock salt structure layered cathode materials,lithium can diffuse in a three-dimensional pathway in Li2MnO3,wich moderate lithium mjgration energy barrier ranges from 0.57 to 0.63 eV.
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