First-principles calculations of the fracture energies of LiFePO4/FePO4 interfaces and the diffusivity of Li in RuO2

Abstract

In this thesis, computational analysis on mechanical behavior of materials for Li ion battery electrodes is conducted using first-principles calculations. Studies on energies involving fracture and diffusion for transition metal oxides is carried out using ab initio calculations based on the density functional theory (DFT). The structure, work of separation, interfacial energies of LiFePO4/FePO4 interfaces, and relevant surface energies are evaluated. The calculations performed concern the separation of various stoichiometric and non-stoichiometric interfacial configurations. Results establish the most stable separations between two phases and required energies for those. Also, migration pathways and energy barriers for diffusion of Li ions in rutile RuO2 are studied in Li-poor and Li-rich phases using the Nudged Elastic Band Method. Diffusivities estimated based on the calculated energy barriers closely agree with experimental values reported in the literature. The results confirm the anisotropic nature of diffusion in one-dimensional c channels along the [001] direction of Li ions in rutile RuO2 and show that Li diffusion in the Li-poor phase is faster than Li diffusion in the Li-rich phase. The finding of fast Li diffusion in the host rutile RuO2 suggests this material is a good ionic conductor of Li transport.