Deep insight into the lithium transportation mechanism and lithium deintercalation study on ε-LiVOPO4 cathode material by atomistic simulation and first-principles method

Abstract

In this work, atomistic simulation together with density functional theory (DFT) method is applied to study the concerted motion of lithium ions and the intercalation/deintercalation mechanism in cathode material ε-LiVOPO4. Two kinds of one dimensional Li + diffusion paths along the direction of →a−→b, that is Li1-2iO5 chains and Li2-2iO5 chains with an energy barrier of 0.066 eV and 0.35 eV, are revealed by molecular dynamics (MD) and bond-valence-energy-landscape mapping (BVEL). At higher temperature, extra diffusion paths between different Li1-2iO5 chains and Li2-2iO5 chains are found. MD studies show that Li + migration along a-axis and b-axis own the same energy barrier of 0.128 eV and the estimated diffusion coefficient at room temperature (RT) is 1.4 × 10−6 cm2 s−1 at the fully lithiated state. The lithium mobility is extremely high for the perfect lattice of ε-LiVOPO. In the process of lithium ion deintercalation, the lithium mobility is gradually depressed. The state of charge (SOC) dependency of Li+ diffusion coefficients shows a downward tendency.