First-Principles Study Of Electronic Structures And Lattice Vibrational Properties On Layered Binary Cathode Materials For Li-ion Batteries

In this thesis,we systematically studied the basic physics properties of layered binary lithium mixed transition metal oxides LiMn_0.5Ni_0.5O₂,LiMn_0.5Co_0.5O₂ and LiCo_0.5Ni_0.5O₂ using first-principles calculations based on the density functional theory.We first studied the structural and electronic properties of LiMn_0.5Ni_0.5O₂,LiMn_0.5Co_0.5O₂,and LiCo_0.5Ni_0.5O₂.The results demonstrate that the rhombohedral structures with R 3 m space group are the most stable configuration for all of these compounds.The electronic properties are studied by analyzing the total density of states and partial density of states.Through analyzing the charge transfer,which affects the Jahn-Teller distortion of Ni³⁺and Mn³⁺,we explain the reason on why the rhombohedral structures are the most stable configurations for the layered binary lithium mixed transition metal oxides.Then,using density functional perturbation theory,we studied the phonon spectrum and the vibrational density of states of LiMn_0.5Ni_0.5O₂ and LiCo_0.5Ni_0.5O₂ compounds as well as thermodynamic properties?Helmholtz free energy,vibrational entropy and constant-volume specific heat capacity?.There is no imaginary frequencies in the calculated phonon spectra,suggesting that the structural stability of the considered phases.In addition,the similar phonon spectra and thermodynamic properties are obtained for the different exchange-correction functional.