First-principles Study On Lattice Dynamics Of Layered Electrode Material In Li-Ion Battery

Electronic structure calculations based on density functional theory(DFT) perfectly explain the physical and chemical properties of many materials. At the same time, electronic structure calculations is playing an increasingly prominent role in performance prediction and functional design of materials. But, so far, a large number of calculations and simulations for electrode materials in Li-Ion battery(LIBs) are only related to the character of ground state(0K). As we know, LIBs usually work at finite temperature, which would results in the difference of structures from its ground state structures. The effect of temperature on the structure of electrode materials is large, which is mainly reflected by the thermodynamic properties. In addition, the theoretical values of potential in LIBs are always different from the experimental values due to the missing of entropy. However, the entropy is an important thermodynamic parameters for the materials. Overall, we can find that the thermodynamic properties of electrode materials are needed to be considered for the theoretical similations of phenomenon and data in the experiments. As a starting point, in this work, we study lattice dynamics properties and thermodynamic properties(such as Helmholtz free energy, vibration, entropy and heat capacity) of layered materials by analyzing the lattice vibrations.On one hand, we investigate lattice dynamics properties of the layered LiMO2(M=Co Ni Mn) cathode material. We analyze the phonon dispersion curves, which help us to understand the lattice vibration characteristics from the atomic scale. In addition, we compare our calculated thermodynamic quantities with the experimental ones, which further confirm our calculated results.On the other hand, we study the structural stabilities and lattice dynamic properties of two dimensional silicane and germanane monolayer under different strains. It is found that the layered configurations could be basically kept under the reasonable tensile strain. However, the structural stability is destroyed under compressive strain, and imaginary frequencies could be found. With the increase of compressive strain, the imaginary frequencies would become more and more obvious Based on the stable systems of silicane and germanane under the tensile strain, we also study the effect of tensile strain on the thermodynamic quantities, and find that the thermodynamics quantities are insensitive to the tensile strain.