Mechanisms of thermal self-diffusion of Li ions in fully lithiated LiFePO4 were investigated using spin-polarized ab initio molecular dynamics calculations. The effect of electron correlation was taken into account with the GGA+U formalism. It was found that Li ion diffusion was not a continuous process but occurred via a series of jumps from one site to another. The predominant process was the hopping between neighboring Li sites around the PO4 groups, which resulted in a zig-zag pathway along the crystallographic b-axis. This was in agreement with neutron diffraction experiments. A secondary process involved the collaborative movements of Fe ions, leading to the formation of antisite defects and promoted Li diffusion across the Li ion channels. The finding of the second mechanism demonstrated the benefits of ab initio molecular dynamics simulation in sampling diffusion pathways that may not be anticipated.

Li Ion Diffusion Mechanisms in LiFePO4: an ab initio Molecular Dynamics Study. Yang, J., Tse, J.S.: Journal of Physical Chemistry A, 2011, 115[45], 13045-9