Calculations of the thermodynamic and kinetic properties of Li1+xV3O8

The phase behavior and kinetic pathways of Li1+xV3O8 are investigated by means of density-functional theory (DFT) and a cluster expansion 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 generalized gradient approximation (GGA) and local-density approximation 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 provide insight into the relevant diffusion pathways and their relationship to structural properties.