Effect of External Electric Field on the Diffusion of Lithium Ions in Bulk LixCoO2: Molecular Dynamics Simulations

In this study we have investigated the diffusion of Li ions in bulk LixCoO2 using molecular dynamics simulations. For the case with no external field, the diffusion coefficient of Li ions is larger when the composition of Li ion (x) in bulk LixCoO2 is smaller. However, the activation energy for Li diffusion is slightly higher, which implies that diffusion behavior of Li ions are influenced by various counteracting factors, such as the concentration of Li ion, width between adjacent CoO2 octahedral layers, and Columbic force field along the diffusion paths. For the case of applied external field, the diffusion coefficient of Li ions decreases for x ≥ 0.8 and increases for x＜0.8 in bulk LixCoO2, when compared to the corresponding case with no external field. The structural analysis of the cases with and without applied field indicates that diffusion of Li ions under external field would fragment the vacancy cluster and form small isolated vacancy clusters, which would hamper the following diffusion of Li ions. Our study demonstrates that the size and distribution of the vacancy clusters influence diffusion of Li ions significantly in bulk LixCoO2 under external field.