Molecular dynamics simulation of lithium ion diffusion in LiCoO2 cathode material
Abstract In this study, lithium ion (Li + ) diffusion inside lithium cobalt oxide (LiCoO 2 ) as a cathode material is investigated using molecular dynamics (MD) simulation. The effect of some important parameters such as voltage, Li + content, and diffusion axis on Li + diffusion coefficient value is explored and compared with the experimental data. The results show that Li + diffusion coefficient in LiCoO 2 material is in the order of 10 − 12 to 10 − 13 cm 2 /s, which is in agreement with the experimental data. Increased voltage value and decreased Li + content raise the Li + diffusion coefficient. In addition, the comparison of the Li + diffusion coefficient along different axes of the crystal layer reveals that transporting lithium ions in a direction perpendicular to the layers of cathode material is more difficult than transporting them in a direction parallel to the layers. It can decrease the diffusion coefficient of Li + by about 20%, especially at high voltage value and low Li + content. But the diffusion coefficient in both directions has the same order of magnitude, which may explain different values of Li + diffusion coefficient in various experimental methods. Replacing Co 3 + with Fe 3 + for increasing the capacity and stability of cathode material may slightly diminish the values of Li + diffusion coefficient, which is in agreement with the experimental results.