First-principles Investigation Of Advanced Battery Materials

With the progress of science and technology and the development of the society,people's demand for energy is increasing.At the same time,human society is facing the energy crisis and the environmental problems caused by traditional energy.Therefore,looking for low price,environmental friendly new energy materials with excellent performance and application safety is of great importance.In recent years,organic–inorganic halide perovskite battery material MAPbI₃,LiFeSO₄ F and a new type of solar cell material Li FePO₄,have become the focus of research.The physical and chemical properties of these new materials were studied by density functional theory in this paper.With the rapid development of numerical algorithms and related theories,the first principles method based on density functional theory?DFT?has become the basic research method to study the fundamental physical properties of materials.In this paper,the geometric structure,magnetic properties and electronic structures of three new energy battery materials are studied.Specific contents are as follows:In the first chapter,the composition,structure and application of the new lithium ion batteries and solar cells were introduced.In the second chapter,the basic theoretical framework of density functional theory and the related calculation methods were introduced.In this paper,to find the appropriate exchange correlation function,theoretical basis and numerical calculation methods of density functional theory?DFT?are summarized,and the application of the theory is discussed.In the third chapter,the theoretical calculation of lithium ion battery material LiFePO₄ is studied.Due to the long life,safety,small volume and high temperature resistance,the environmental friendly LiFePO₄ secondary battery has attracted more and more attention.However,the low diffusion rate of lithium ion has prevented the development of its commercialization.In this chapter,the electronic structure and properties of LiFePO₄ are calculated by first principles method: The diffusion barrier of LiFePO₄ under two different point defect concentrations?LixFePO₄,x=0.0625/x=0.9375?were estimated using CI-NEB?climbing image Nudged Elastic Band method?method and hybrid density functional theory,which explained the diffusion mechanism of lithium ion,hole and polaron.It provides a strong theoretical basis for understanding and improving the properties of materials.The fourth chapter is the first principle study on the vibrational spectra of lithium iron fluoride crystals.Lithium ferric fluoride?LiFeSO₄F?is a new type of anionic cathode material,first synthesized by Recham et al.In 2010.In this paper,the first principles method based on density functional perturbation theory?DFPT?was used to study the lattice vibrational properties of tavorite Li FeSO₄ F systematically.The calculated Raman scattering spectra are in agreement with our experimental data.At the same time,with the help of group theory and spectral correlation,the lattice vibration properties of tavorite LiFeSO₄ F and the identification of vibrational modes are analyzed,which provides an important theoretical basis for the study of LiFeSO₄ F series materials.The fifth chapter is about the first principles calculation of the migration mechanism of hydrogen in the solar cell material MAPb I₃.Organic inorganic composite perovskite solar cell?MAPbI₃?is one of the new energy development hot spots in recent years.Due to the important effect of ion migration on the performance and stability of perovskite solar cells,the study of ion mobility has become the focus of academic research.In this chapter,based on the first principles calculation of density functional theory,the electronic structure of MAPb I₃ and the hydrogen impurities with three different charged states are analyzed.After the calculation of the proton?H+?migration barrier in the MAPbI₃ crystal,the diffusion mechanism of the proton as the interstitial impurity in MAPb I₃ and the influence on the electronic structure of MAPb I₃ were analyzed.