Molecular dynamics simulation of lithium ion diffusion in LiCoO2 cathode material

• Li+ diffusion coefficient in LiCoO2 material is in the order of 10− 12 to 10− 13 cm2/s.
• Increased voltage value and decreased Li+ content raise the Li+ diffusion coefficient.
• Li+ transport in a direction perpendicular to the layers of LiCoO2 is difficult.
• Replacing Co3 + with Fe3 + may slightly diminish the values of Li+ diffusion coefficients.

In this study, lithium ion (Li+) diffusion inside lithium cobalt oxide (LiCoO2) 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 LiCoO2 material is in the order of 10− 12 to 10− 13 cm2/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 Co3 + with Fe3 + 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.