The phase behavior and kinetic pathways of Li1+xV3O8 are investigated by means of density functional theory (DFT) and a cluster expansion (CE) method that approximates the system Hamiltonian in order to identify the lowest energy configurations. Although DFT calculations predict the correct ground state for a given composition, both GGA and LDA fail to obtain phase stability consistent with experiment due to strongly localized vanadium 3d electrons. A DFT+U method recovers the correct phase stability for an optimized U value of 3.0 eV. GGA+U calculations with this value of U predict electronic structures that qualitatively agree with experiment. The resulting calculations indicate solid solution behavior from Li1V3O8 to Li2.5V3O8 and two-phase coexistence between Li2.5V3O8 and Li4V3O8. Analysis of the lithiation sequence from Li1V3O8 to Li2.5V3O8 reveals the mechanism by which lithium intercalation proceeds in this material. Calculations of lithium migration energies for different lithium concentrations and configurations provides insight into the relevant diffusion pathways and their relationship to structural properties.

Cubic spinel Li1+xTi2O4 is a promising electrode material as it exhibits a high lithium diffusivity and undergoes minimal changes in lattice parameters during lithiation and delithiation, thereby ensuring favorable cycleability. The present work is a multi-physics and multi-scale study of Li1+xTi2O4 that combines first principles computations of thermodynamic and kinetic properties with continuum scale modeling of lithiation-delithiation kinetics. Density functional theory calculations and statistical mechanics methods are used to calculate lattice parameters, elastic coefficients, thermodynamic potentials, migration barriers and Li diffusion coefficients. These quantities then inform a phase field framework to model the coupled chemo-mechanical evolution of electrode particles. Several case studies accounting for either homogeneous or heterogeneous nucleation are considered to explore the temporal evolution of maximum principle stress values, which serve to indicate stress localization and the potential for crack initiation, during lithiation and delithiation.