The diffusion mechanism of Li ions in the olivine LiFePO4 was investigated from first-principles calculations. The energy barriers for possible spatial hopping pathways were calculated with the adiabatic trajectory method. The calculations showed that the energy barriers running along the c axis were about 0.6, 1.2 and 1.5eV for LiFePO4, FePO4 and Li0.5FePO4, respectively. However, the other migration pathways have much higher energy barriers resulting in very low probability of Li-ion migration. This means that the diffusion in LiFePO4 was one dimensional. The one-dimensional diffusion behavior had also been shown with full ab initio molecular dynamics simulation, through which the diffusion behavior was directly observed.

First-Principles Study of Li Ion Diffusion in LiFePO4. C.Ouyang, S.Shi, Z.Wang, X.Huang, L.Chen: Physical Review B, 2004, 69[10], 104303 (5pp)